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{{task|Percolation Simulations}}{{Percolation Simulation}} Given an $M \times N$ rectangular array of cells numbered $\mathrm\left\{cell\right\}\left[0..M-1, 0..N-1\right]$, assume $M$ is horizontal and $N$ is downwards. Each $\mathrm\left\{cell\right\}\left[m, n\right]$ is bounded by (horizontal) walls $\mathrm\left\{hwall\right\}\left[m, n\right]$ and $\mathrm\left\{hwall\right\}\left[m+1, n\right]$; (vertical) walls $\mathrm\left\{vwall\right\}\left[m, n\right]$ and $\mathrm\left\{vwall\right\}\left[m, n+1\right]$

Assume that the probability of any wall being present is a constant $p$ where : $0.0 \le p \le 1.0$ Except for the outer horizontal walls at $m = 0$ and $m = M$ which are always present.

;The task: Simulate pouring a fluid onto the top surface ($n = 0$) where the fluid will enter any empty cell it is adjacent to if there is no wall between where it currently is and the cell on the other side of the (missing) wall.

The fluid does not move beyond the horizontal constraints of the grid.

The fluid may move “up” within the confines of the grid of cells. If the fluid reaches a bottom cell that has a missing bottom wall then the fluid can be said to 'drip' out the bottom at that point.

Given $p$ repeat the percolation $t$ times to estimate the proportion of times that the fluid can percolate to the bottom for any given $p$.

Show how the probability of percolating through the random grid changes with $p$ going from $0.0$ to $1.0$ in $0.1$ increments and with the number of repetitions to estimate the fraction at any given $p$ as $t = 100$.

Use an $M=10, N=10$ grid of cells for all cases.

Optionally depict fluid successfully percolating through a grid graphically.

## C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// cell states
#define FILL 1
#define RWALL 2 // right wall
#define BWALL 4 // bottom wall

typedef unsigned int c_t;

c_t *cells, *start, *end;
int m, n;

void make_grid(double p, int x, int y)
{
int i, j, thresh = RAND_MAX * p;
m = x, n = y;

// Allocate two addition rows to avoid checking bounds.
// Bottom row is also required by drippage
start = realloc(start, m * (n + 2) * sizeof(c_t));
cells = start + m;

for (i = 0; i < m; i++)
start[i] = BWALL | RWALL;

for (i = 0, end = cells; i < y; i++) {
for (j = x; --j; )
*end++ = (rand() < thresh ? BWALL : 0)
|(rand() < thresh ? RWALL : 0);
*end++ = RWALL | (rand() < thresh ? BWALL: 0);
}
memset(end, 0, sizeof(c_t) * m);
}

void show_grid(void)
{
int i, j;

for (j = 0; j < m; j++) printf("+--");
puts("+");

for (i = 0; i <= n; i++) {
putchar(i == n ? ' ' : '|');
for (j = 0; j < m; j++) {
printf((cells[i*m + j] & FILL) ? "[]" : "  ");
putchar((cells[i*m + j] & RWALL) ? '|' : ' ');
}
putchar('\n');

if (i == n) return;

for (j = 0; j < m; j++)
printf((cells[i*m + j] & BWALL) ? "+--" : "+  ");
puts("+");
}
}

int fill(c_t *p)
{
if ((*p & FILL)) return 0;
*p |= FILL;
if (p >= end) return 1; // success: reached bottom row

return  ( !(p[ 0] & BWALL) && fill(p + m) ) ||
( !(p[ 0] & RWALL) && fill(p + 1) ) ||
( !(p[-1] & RWALL) && fill(p - 1) ) ||
( !(p[-m] & BWALL) && fill(p - m) );
}

int percolate(void)
{
int i;
for (i = 0; i < m && !fill(cells + i); i++);

return i < m;
}

int main(void)
{
make_grid(.5, 10, 10);
percolate();
show_grid();

int cnt, i, p;

puts("\nrunning 10x10 grids 10000 times for each p:");
for (p = 1; p < 10; p++) {
for (cnt = i = 0; i < 10000; i++) {
make_grid(p / 10., 10, 10);
cnt += percolate();
//show_grid(); // don't
}
printf("p = %3g: %.4f\n", p / 10., (double)cnt / i);
}

free(start);
return 0;
}


{{out}}


+--+--+--+--+--+--+--+--+--+--+
|[]|[] []|[] [] [] [] []      |
+  +  +  +--+--+--+--+  +  +--+
|[]|[]|[]|  |         [] []|  |
+  +--+  +--+--+--+  +--+  +  +
|[] [] [] []|        |   []|  |
+--+  +--+--+  +--+  +--+  +--+
|  |[]|     |  |        |[]   |
+--+--+  +  +  +  +  +--+  +  +
|     |  |     |         []   |
+--+  +  +--+  +--+--+  +  +--+
|  |     |     |[] [] [] []|  |
+  +  +  +--+  +  +--+--+--+--+
|  |  |     |   []   |  |  |  |
+--+  +--+--+--+  +  +  +--+  +
|  |  |  |  |  |[]|           |
+--+  +  +  +  +  +--+  +  +  +
|  |  |  |   [] []|  |  |  |  |
+--+  +--+--+  +--+  +  +  +  +
|  |     |   []|           |  |
+--+  +--+--+  +  +--+--+  +  +
[]

running 10x10 grids 10000 times for each p:
p = 0.1: 1.0000
p = 0.2: 1.0000
p = 0.3: 0.9958
p = 0.4: 0.9123
p = 0.5: 0.5014
p = 0.6: 0.0791
p = 0.7: 0.0037
p = 0.8: 0.0000
p = 0.9: 0.0000



## C++

{{trans|D}}

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>

using namespace std;

class Grid {
public:
Grid(const double p, const int x, const int y) : m(x), n(y) {
const int thresh = static_cast<int>(RAND_MAX * p);

// Allocate two addition rows to avoid checking bounds.
// Bottom row is also required by drippage
start = new cell[m * (n + 2)];
cells = start + m;
for (auto i = 0; i < m; i++) start[i] = RBWALL;
end = cells;
for (auto i = 0; i < y; i++) {
for (auto j = x; --j;)
*end++ = (rand() < thresh ? BWALL : 0) | (rand() < thresh ? RWALL : 0);
*end++ = RWALL | (rand() < thresh ? BWALL : 0);
}
memset(end, 0u, sizeof(cell) * m);
}

~Grid() {
delete[] start;
cells = 0;
start = 0;
end = 0;
}

int percolate() const {
auto i = 0;
for (; i < m && !fill(cells + i); i++);
return i < m;
}

void show() const {
for (auto j = 0; j < m; j++)
cout << ("+-");
cout << '+' << endl;

for (auto i = 0; i <= n; i++) {
cout << (i == n ? ' ' : '|');
for (auto j = 0; j < m; j++) {
cout << ((cells[i * m + j] & FILL) ? "#" : " ");
cout << ((cells[i * m + j] & RWALL) ? '|' : ' ');
}
cout << endl;

if (i == n) return;

for (auto j = 0; j < m; j++)
cout << ((cells[i * m + j] & BWALL) ? "+-" : "+ ");
cout << '+' << endl;
}
}

private:
enum cell_state {
FILL   = 1 << 0,
RWALL  = 1 << 1,       // right wall
BWALL  = 1 << 2,       // bottom wall
RBWALL = RWALL | BWALL // right/bottom wall
};

typedef unsigned int cell;

bool fill(cell* p) const {
if ((*p & FILL)) return false;
*p |= FILL;
if (p >= end) return true; // success: reached bottom row

return (!(p[0] & BWALL) && fill(p + m)) || (!(p[0] & RWALL) && fill(p + 1))
||(!(p[-1] & RWALL) && fill(p - 1)) || (!(p[-m] & BWALL) && fill(p - m));
}

cell* cells;
cell* start;
cell* end;
const int m;
const int n;
};

int main() {
const auto M = 10, N = 10;
const Grid grid(.5, M, N);
grid.percolate();
grid.show();

const auto C = 10000;
cout << endl << "running " << M << "x" << N << " grids " << C << " times for each p:" << endl;
for (auto p = 1; p < M; p++) {
auto cnt = 0, i = 0;
for (; i < C; i++)
cnt += Grid(p / static_cast<double>(M), M, N).percolate();
cout << "p = " << p / static_cast<double>(M) << ": " << static_cast<double>(cnt) / i << endl;
}

return EXIT_SUCCESS;
}


## D

{{trans|C}}

import std.stdio, std.random, std.array, std.range, std.algorithm;

struct Grid {
// Not enforced by runtime and type system:
// a Cell must contain only the flags bits.
alias Cell = uint;

enum : Cell { // Cell states (bit flags).
empty      = 0,
filled     = 1,
rightWall  = 2,
bottomWall = 4
}

const size_t nc, nr;
Cell[] cells;

this(in size_t nRows, in size_t nCols) pure nothrow {
nr = nRows;
nc = nCols;

// Allocate two addition rows to avoid checking bounds.
// Bottom row is also required by drippage.
cells = new Cell[nc * (nr + 2)];
}

void initialize(in double prob, ref Xorshift rng) {
cells[0 .. nc] = bottomWall | rightWall; // First row.

uint pos = nc;
foreach (immutable r; 1 .. nr + 1) {
foreach (immutable c; 1 .. nc)
cells[pos++] = (uniform01 < prob ?bottomWall : empty) |
(uniform01 < prob ? rightWall : empty);
cells[pos++] = rightWall |
(uniform01 < prob ? bottomWall : empty);
}

cells[$- nc ..$] = empty; // Last row.
}

bool percolate() pure nothrow @nogc {
bool fill(in size_t i) pure nothrow @nogc {
if (cells[i] & filled)
return false;

cells[i] |= filled;

if (i >= cells.length - nc)
return true; // Success: reached bottom row.

return (!(cells[i]      & bottomWall) && fill(i + nc)) ||
(!(cells[i]      & rightWall)  && fill(i + 1)) ||
(!(cells[i - 1]  & rightWall)  && fill(i - 1)) ||
(!(cells[i - nc] & bottomWall) && fill(i - nc));
}

return iota(nc, nc + nc).any!fill;
}

void show() const {
writeln("+-".replicate(nc), '+');

foreach (immutable r; 1 .. nr + 2) {
write(r == nr + 1 ? ' ' : '|');
foreach (immutable c; 0 .. nc) {
immutable cell = cells[r * nc + c];
write((cell & filled) ? (r <= nr ? '#' : 'X') : ' ');
write((cell & rightWall) ? '|' : ' ');
}
writeln;

if (r == nr + 1)
return;

foreach (immutable c; 0 .. nc)
write((cells[r * nc + c] & bottomWall) ? "+-" : "+ ");
'+'.writeln;
}
}
}

void main() {
enum uint nr = 10, nc = 10; // N. rows and columns of the grid.
enum uint nTries = 10_000;  // N. simulations for each probability.
enum uint nStepsProb = 10;  // N. steps of probability.

auto rng = Xorshift(2);
auto g = Grid(nr, nc);
g.initialize(0.5, rng);
g.percolate;
g.show;

writefln("\nRunning %dx%d grids %d times for each p:",
nr, nc, nTries);
foreach (immutable p; 0 .. nStepsProb) {
immutable probability = p / double(nStepsProb);
uint nPercolated = 0;
foreach (immutable i; 0 .. nTries) {
g.initialize(probability, rng);
nPercolated += g.percolate;
}
writefln("p = %0.2f: %.4f",
probability, nPercolated / double(nTries));
}
}


{{out}}

+-+-+-+-+-+-+-+-+-+-+
|#|#|#|#|     | |   |
+ +-+-+ +-+-+-+ +-+-+
|#| |  #  | | |   | |
+ +-+-+ + +-+-+ + +-+
|#|# #|#|   | |     |
+ +-+ + +-+ + + +-+ +
|#|# #|#|   | |   | |
+-+ + + + +-+-+-+-+-+
|# # # # #  | |   | |
+ + + + + + + +-+ +-+
|#|# # #|# # #  |   |
+-+ + + +-+-+ + + + +
| |#|# #| | |#      |
+-+-+-+-+ +-+ +-+-+-+
| |   |    # #|     |
+-+-+-+ +-+ +-+-+-+ +
| | |      # # #    |
+ + +-+ +-+-+-+ +-+ +
|     |   |   |#    |
+ +-+ + + + +-+ + + +
X

Running 10x10 grids 10000 times for each p:
p = 0.00: 1.0000
p = 0.10: 1.0000
p = 0.20: 1.0000
p = 0.30: 0.9973
p = 0.40: 0.9177
p = 0.50: 0.5050
p = 0.60: 0.0880
p = 0.70: 0.0035
p = 0.80: 0.0001
p = 0.90: 0.0000


With LDC2 compiler this code runs in 0.26 seconds (almost two times faster than the C entry).

## Go

{{trans|C}}

package main

import (
"fmt"
"math/rand"
"strings"
"time"
)

func main() {
const (
m, n           = 10, 10
t              = 1000
minp, maxp, Δp = 0.1, 0.99, 0.1
)

// Purposely don't seed for a repeatable example grid:
g := NewGrid(.5, m, n)
g.Percolate()
fmt.Println(g)

rand.Seed(time.Now().UnixNano()) // could pick a better seed
for p := float64(minp); p < maxp; p += Δp {
count := 0
for i := 0; i < t; i++ {
g := NewGrid(p, m, n)
if g.Percolate() {
count++
}
}
fmt.Printf("p=%.2f, %.3f\n", p, float64(count)/t)
}
}

type cell struct {
full        bool
right, down bool // true if open to the right (x+1) or down (y+1)
}

type grid struct {
cell [][]cell // row first, i.e. [y][x]
}

func NewGrid(p float64, xsize, ysize int) *grid {
g := &grid{cell: make([][]cell, ysize)}
for y := range g.cell {
g.cell[y] = make([]cell, xsize)
for x := 0; x < xsize-1; x++ {
if rand.Float64() > p {
g.cell[y][x].right = true
}
if rand.Float64() > p {
g.cell[y][x].down = true
}
}
if rand.Float64() > p {
g.cell[y][xsize-1].down = true
}
}
return g
}

var (
full  = map[bool]string{false: "  ", true: "**"}
hopen = map[bool]string{false: "--", true: "  "}
vopen = map[bool]string{false: "|", true: " "}
)

func (g *grid) String() string {
var buf strings.Builder
// Don't really need to call Grow but it helps avoid multiple
// reallocations if the size is large.
buf.Grow((len(g.cell) + 1) * len(g.cell[0]) * 7)

for _ = range g.cell[0] {
buf.WriteString("+")
buf.WriteString(hopen[false])
}
buf.WriteString("+\n")
for y := range g.cell {
buf.WriteString(vopen[false])
for x := range g.cell[y] {
buf.WriteString(full[g.cell[y][x].full])
buf.WriteString(vopen[g.cell[y][x].right])
}
buf.WriteByte('\n')
for x := range g.cell[y] {
buf.WriteString("+")
buf.WriteString(hopen[g.cell[y][x].down])
}
buf.WriteString("+\n")
}
ly := len(g.cell) - 1
for x := range g.cell[ly] {
buf.WriteByte(' ')
buf.WriteString(full[g.cell[ly][x].down && g.cell[ly][x].full])
}
return buf.String()
}

func (g *grid) Percolate() bool {
for x := range g.cell[0] {
if g.fill(x, 0) {
return true
}
}
return false
}

func (g *grid) fill(x, y int) bool {
if y >= len(g.cell) {
return true // Out the bottom
}
if g.cell[y][x].full {
}
g.cell[y][x].full = true

if g.cell[y][x].down && g.fill(x, y+1) {
return true
}
if g.cell[y][x].right && g.fill(x+1, y) {
return true
}
if x > 0 && g.cell[y][x-1].right && g.fill(x-1, y) {
return true
}
if y > 0 && g.cell[y-1][x].down && g.fill(x, y-1) {
return true
}
return false
}


{{out}}


+--+--+--+--+--+--+--+--+--+--+
|** ** **|  |  |     |  |  |  |
+  +--+  +--+--+  +--+--+--+  +
|**|  |** **|  |     |     |  |
+--+  +--+  +  +  +--+  +  +--+
|     |   **|  |              |
+--+  +--+  +--+--+--+--+--+--+
|     |   ** **|        |     |
+--+  +  +--+  +  +--+  +--+  +
|           |** ** **|     |  |
+  +  +--+  +--+  +  +--+  +--+
|  |  |  |   ** ** ** **|  |  |
+  +--+--+  +  +--+--+  +--+--+
|  |** ** **|**|**|  |** ** **|
+  +  +  +  +  +  +--+  +--+  +
|** **|**|** ** **|  |** ** **|
+  +  +--+--+--+--+  +  +--+  +
|**|** ** **|     |  |**|  |**|
+  +--+--+--+  +  +--+--+--+--+
|**               |  |  |  |  |
+  +  +  +  +--+--+  +--+--+  +
**
p=0.10, 1.000
p=0.20, 1.000
p=0.30, 0.998
p=0.40, 0.915
p=0.50, 0.502
p=0.60, 0.081
p=0.70, 0.002
p=0.80, 0.000
p=0.90, 0.000



{-# LANGUAGE OverloadedStrings #-}
import Data.Array.Unboxed
import Data.List
import Formatting

data Field = Field { f :: UArray (Int, Int) Char
, hWall :: UArray (Int, Int) Bool
, vWall :: UArray (Int, Int) Bool
}

-- Start percolating some seepage through a field.
-- Recurse to continue percolation with new seepage.
percolateR :: [(Int, Int)] -> Field -> (Field, [(Int,Int)])
percolateR [] (Field f h v) = (Field f h v, [])
percolateR seep (Field f h v) =
let ((xLo,yLo),(xHi,yHi)) = bounds f
validSeep = filter (\p@(x,y) ->    x >= xLo
&& x <= xHi
&& y >= yLo
&& y <= yHi
&& f!p == ' ') $nub$ sort seep

north (x,y) = if v ! (x  ,y  ) then [] else [(x  ,y-1)]
south (x,y) = if v ! (x  ,y+1) then [] else [(x  ,y+1)]
west  (x,y) = if h ! (x  ,y  ) then [] else [(x-1,y  )]
east  (x,y) = if h ! (x+1,y  ) then [] else [(x+1,y  )]
neighbors (x,y) = north(x,y) ++ south(x,y) ++ west(x,y) ++ east(x,y)

in  percolateR
(concatMap neighbors validSeep)
(Field (f // map (\p -> (p,'.')) validSeep) h v)

-- Percolate a field;  Return the percolated field.
percolate :: Field -> Field
percolate start@(Field f _ _) =
let ((_,_),(xHi,_)) = bounds f
(final, _) = percolateR [(x,0) | x <- [0..xHi]] start
in final

-- Generate a random field.
initField :: Int -> Int -> Double -> Rand StdGen Field
initField width height threshold = do
let f = listArray ((0,0), (width-1, height-1)) $repeat ' ' hrnd <- fmap (<threshold) <$> getRandoms
let h0 = listArray ((0,0),(width, height-1)) hrnd
h1 = h0 // [((0,y), True) | y <- [0..height-1]]     -- close left
h2 = h1 // [((width,y), True) | y <- [0..height-1]] -- close right

vrnd <- fmap (<threshold) <$> getRandoms let v0 = listArray ((0,0),(width-1, height)) vrnd v1 = v0 // [((x,0), True) | x <- [0..width-1]] -- close top return$ Field f h2 v1

-- Assess whether or not percolation reached bottom of field.
leaks :: Field -> [Bool]
leaks (Field f _ v) =
let ((xLo,_),(xHi,yHi)) = bounds f
in [f!(x,yHi)=='.' && not (v!(x,yHi+1)) | x <- [xLo..xHi]]

-- Run test once; Return bool indicating success or failure.
oneTest :: Int -> Int -> Double -> Rand StdGen Bool
oneTest width height threshold =
or.leaks.percolate <$> initField width height threshold -- Run test multple times; Return the number of tests that pass. multiTest :: Int -> Int -> Int -> Double -> Rand StdGen Double multiTest testCount width height threshold = do results <- replicateM testCount$ oneTest width height threshold
let leakyCount = length $filter id results return$ fromIntegral leakyCount / fromIntegral testCount

-- Helper function for display
alternate :: [a] -> [a] -> [a]
alternate [] _ = []
alternate (a:as) bs = a : alternate bs as

-- Display a field with walls and leaks.
showField :: Field -> IO ()
showField field@(Field a h v) =  do
let ((xLo,yLo),(xHi,yHi)) = bounds a
fLines =  [ [ a!(x,y) | x <- [xLo..xHi]] | y <- [yLo..yHi]]
hLines =  [ [ if h!(x,y) then '|' else ' ' | x <- [xLo..xHi+1]] | y <- [yLo..yHi]]
vLines =  [ [ if v!(x,y) then '-' else ' ' | x <- [xLo..xHi]] | y <- [yLo..yHi+1]]
lattice =  [ [ '+' | x <- [xLo..xHi+1]] | y <- [yLo..yHi+1]]

hDrawn = zipWith alternate hLines fLines
vDrawn = zipWith alternate lattice vLines
mapM_ putStrLn $alternate vDrawn hDrawn let leakLine = [ if l then '.' else ' ' | l <- leaks field] putStrLn$ alternate (repeat ' ') leakLine

main :: IO ()
main = do
g <- getStdGen
let threshold = 0.45
(startField, g2) = runRand (initField 10 10 threshold) g

putStrLn ("Unpercolated field with " ++ show threshold ++ " threshold.")
putStrLn ""
showField startField

putStrLn ""
putStrLn "Same field after percolation."
putStrLn ""
showField $percolate startField let testCount = 10000 densityCount = 10 putStrLn "" putStrLn ("Results of running percolation test " ++ show testCount ++ " times with thresholds ranging from 0/" ++ show densityCount ++ " to " ++ show densityCount ++ "/" ++ show densityCount ++ " .") let densities = [0..densityCount] let tests = sequence [multiTest testCount 10 10 v | density <- densities, let v = fromIntegral density / fromIntegral densityCount ] let results = zip densities (evalRand tests g2) mapM_ print [format ("p=" % int % "/" % int % " -> " % fixed 4) density densityCount x | (density,x) <- results]  {{out}}  Unpercolated field with 0.45 threshold. +-+-+-+-+-+-+-+-+-+-+ | | | | | | | | +-+-+ +-+ + + + + +-+ | | | | | | | | + + +-+-+ + +-+-+ + + | | | | + +-+-+-+ +-+-+ +-+ + | | | | | | + +-+ + + +-+-+ + +-+ | | | | | | +-+-+ + + + + +-+ + + | | | | | | | | +-+ + + + + + + +-+-+ | | | | | + + + + + +-+ +-+ + + | | | | | | | | | + + + +-+-+-+-+-+ + + | | | | | + +-+ +-+ +-+ + + +-+ | | | | | | + + + + +-+ +-+-+-+ + Same field after percolation. +-+-+-+-+-+-+-+-+-+-+ |. . . .|.|.|.|.|.|.| +-+-+ +-+ + + + + +-+ | |.|. . . .|.|.|.|.| + + +-+-+ + +-+-+ + + | |. . . . .|. . . .| + +-+-+-+ +-+-+ +-+ + | |. . .|.|. . . .|.| + +-+ + + +-+-+ + +-+ | |. . .|. . . .|.|.| +-+-+ + + + + +-+ + + | |.|. .|.|.|.|. . .| +-+ + + + + + + +-+-+ |. . . . .|. .|. .|.| + + + + + +-+ +-+ + + |.|.|.|.|. . .| |.|.| + + + +-+-+-+-+-+ + + |.|. . . .|. . .|. .| + +-+ +-+ +-+ + + +-+ |.| |.|. . . . . .| | + + + + +-+ +-+-+-+ + . . . . Results of running percolation test 10000 times with thresholds ranging from 0/10 to 10/10 . "p=0/10 -> 1.0000" "p=1/10 -> 1.0000" "p=2/10 -> 1.0000" "p=3/10 -> 0.9969" "p=4/10 -> 0.9171" "p=5/10 -> 0.5026" "p=6/10 -> 0.0901" "p=7/10 -> 0.0025" "p=8/10 -> 0.0000" "p=9/10 -> 0.0000" "p=10/10 -> 0.0000"  ## Julia {{works with|Julia|0.6}} {{trans|Python}} using Distributions struct Grid cells::BitArray{2} hwall::BitArray{2} vwall::BitArray{2} end function Grid(p::AbstractFloat, m::Integer=10, n::Integer=10) cells = fill(false, m, n) hwall = rand(Bernoulli(p), m + 1, n) vwall = rand(Bernoulli(p), m, n + 1) vwall[:, 1] = true vwall[:, end] = true return Grid(cells, hwall, vwall) end function Base.show(io::IO, g::Grid) H = (" .", " _") V = (":", "|") C = (" ", "#") ind = findfirst(g.cells[end, :] .& .!g.hwall[end, :]) percolated = !iszero(ind) println(io, "$(size(g.cells, 1))×$(size(g.cells, 2))$(percolated ? "Percolated" : "Not percolated") grid")
for r in 1:size(g.cells, 1)
println(io, "    ", join(H[w+1] for w in g.hwall[r, :]))
println(io, " $(r % 10)) ", join(V[w+1] * C[c+1] for (w, c) in zip(g.vwall[r, :], g.cells[r, :]))) end println(io, " ", join(H[w+1] for w in g.hwall[end, :])) if percolated println(io, " !) ", " " ^ (ind - 1), '#') end end function floodfill!(m::Integer, n::Integer, cells::AbstractMatrix{<:Integer}, hwall::AbstractMatrix{<:Integer}, vwall::AbstractMatrix{<:Integer}) # fill cells cells[m, n] = true percolated = false # bottom if m < size(cells, 1) && !hwall[m+1, n] && !cells[m+1, n] percolated = percolated || floodfill!(m + 1, n, cells, hwall, vwall) # The Bottom elseif m == size(cells, 1) && !hwall[m+1, n] return true end # left if n > 1 && !vwall[m, n] && !cells[m, n-1] percolated = percolated || floodfill!(m, n - 1, cells, hwall, vwall) end # right if n < size(cells, 2) && !vwall[m, n+1] && !cells[m, n+1] percolated = percolated || floodfill!(m, n + 1, cells, hwall, vwall) end # top if m > 1 && !hwall[m, n] && !cells[m-1, n] percolated = percolated || floodfill!(m - 1, n, cells, hwall, vwall) end return percolated end function pourontop!(g::Grid) m, n = 1, 1 percolated = false while !percolated && n ≤ size(g.cells, 2) percolated = !g.hwall[m, n] && floodfill!(m, n, g.cells, g.hwall, g.vwall) n += 1 end return percolated end function main(probs, nrep::Integer=1000) sampleprinted = false pcount = zeros(Int, size(probs)) for (i, p) in enumerate(probs), _ in 1:nrep g = Grid(p) percolated = pourontop!(g) if percolated pcount[i] += 1 if !sampleprinted println(g) sampleprinted = true end end end return pcount ./ nrep end probs = collect(10:-1:0) ./ 10 percprobs = main(probs) println("Fraction of 1000 tries that percolate through:") for (pr, pp) in zip(probs, percprobs) @printf("\tp = %.3f ⇒ freq. = %5.3f\n", pr, pp) end  {{out}} 10×10 Percolated grid _ . . _ _ _ . _ . . 1) | |#:#| | : | : | : _ _ . _ _ _ _ _ . _ 2) | | |#| : : | : | | _ _ . _ _ _ _ _ _ . 3) | | |#:#| : | : | : . _ _ . _ _ _ . _ _ 4) | | | :#: : | | | | . _ _ . _ _ _ . _ _ 5) | | : |#| | : | | : _ . _ . _ _ . . . _ 6) | | | |#| | | | | | . . _ . _ _ _ . . . 7) | |#:#:#: | | : | | _ . . _ . . . . _ _ 8) | |#|#| | | : | | | _ . . _ _ _ . _ _ _ 9) |#:#|#| : : | : | | . _ _ _ _ . _ _ _ . 0) |#: | : | | | : : | . . _ _ _ _ . _ _ _ !) # Fraction of 1000 tries that percolate through: p = 1.000 ⇒ freq. = 0.000 p = 0.900 ⇒ freq. = 0.000 p = 0.800 ⇒ freq. = 0.000 p = 0.700 ⇒ freq. = 0.001 p = 0.600 ⇒ freq. = 0.064 p = 0.500 ⇒ freq. = 0.470 p = 0.400 ⇒ freq. = 0.895 p = 0.300 ⇒ freq. = 0.997 p = 0.200 ⇒ freq. = 1.000 p = 0.100 ⇒ freq. = 1.000 p = 0.000 ⇒ freq. = 1.000  ## Kotlin {{trans|C}} // version 1.2.10 import java.util.Random val rand = Random() const val RAND_MAX = 32767 // cell states const val FILL = 1 const val RWALL = 2 // right wall const val BWALL = 4 // bottom wall val x = 10 val y = 10 var grid = IntArray(x * (y + 2)) var cells = 0 var end = 0 var m = 0 var n = 0 fun makeGrid(p: Double) { val thresh = (p * RAND_MAX).toInt() m = x n = y grid.fill(0) // clears grid for (i in 0 until m) grid[i] = BWALL or RWALL cells = m end = m for (i in 0 until y) { for (j in x - 1 downTo 1) { val r1 = rand.nextInt(RAND_MAX + 1) val r2 = rand.nextInt(RAND_MAX + 1) grid[end++] = (if (r1 < thresh) BWALL else 0) or (if (r2 < thresh) RWALL else 0) } val r3 = rand.nextInt(RAND_MAX + 1) grid[end++] = RWALL or (if (r3 < thresh) BWALL else 0) } } fun showGrid() { for (j in 0 until m) print("+--") println("+") for (i in 0..n) { print(if (i == n) " " else "|") for (j in 0 until m) { print(if ((grid[i * m + j + cells] and FILL) != 0) "[]" else " ") print(if ((grid[i * m + j + cells] and RWALL) != 0) "|" else " ") } println() if (i == n) return for (j in 0 until m) { print(if ((grid[i * m + j + cells] and BWALL) != 0) "+--" else "+ ") } println("+") } } fun fill(p: Int): Boolean { if ((grid[p] and FILL) != 0) return false grid[p] = grid[p] or FILL if (p >= end) return true // success: reached bottom row return (((grid[p + 0] and BWALL) == 0) && fill(p + m)) || (((grid[p + 0] and RWALL) == 0) && fill(p + 1)) || (((grid[p - 1] and RWALL) == 0) && fill(p - 1)) || (((grid[p - m] and BWALL) == 0) && fill(p - m)) } fun percolate(): Boolean { var i = 0 while (i < m && !fill(cells + i)) i++ return i < m } fun main(args: Array<String>) { makeGrid(0.5) percolate() showGrid() println("\nrunning$x x $y grids 10,000 times for each p:") for (p in 1..9) { var cnt = 0 val pp = p / 10.0 for (i in 0 until 10_000) { makeGrid(pp) if (percolate()) cnt++ } println("p = %3g: %.4f".format(pp, cnt.toDouble() / 10_000)) } }  Sample output:  +--+--+--+--+--+--+--+--+--+--+ |[]|[] [] [] [] []| | | | | +--+--+--+--+--+ +--+ + + + | | | | []| | +--+--+--+--+--+ + +--+ + + | | | | |[] []| | + + + + + +--+--+--+--+--+ | | | [] [] []| | | +--+--+ + +--+--+--+--+--+ + | | |[] []| | | | +--+--+ + + + +--+ +--+--+ | | | |[]|[]| | | | +--+ +--+--+ +--+--+ + + + | | | []| | | | | +--+ + + + +--+--+ + + + | | |[] []| | | + +--+--+ +--+ +--+ + +--+ | | [] | | | | + + +--+ + +--+--+--+--+ + | [] | | | | + +--+--+ + +--+--+ +--+ + [] running 10 x 10 grids 10,000 times for each p: p = 0.100000: 1.0000 p = 0.200000: 1.0000 p = 0.300000: 0.9968 p = 0.400000: 0.9184 p = 0.500000: 0.5047 p = 0.600000: 0.0828 p = 0.700000: 0.0034 p = 0.800000: 0.0000 p = 0.900000: 0.0000  ## Perl {{trans|Perl 6}} my @bond; my$grid = 10;
my $water = '▒';$D{$_} =$i++ for qw<DeadEnd Up Right Down Left>;

sub percolate {
generate(shift || 0.6);
fill(my $x = 1,my$y = 0);
my @stack;

while () {
if (my $dir = direction($x,$y)) { push @stack, [$x,$y]; ($x,$y) = move($dir, $x,$y)
} else {
return 0 unless @stack;
($x,$y) = @{pop @stack}
}
return 1 if $y ==$#bond;
}
}

sub direction {
my($x,$y) = @_;
return $D{Down} if$bond[$y+1][$x  ] =~ / /;
return $D{Left} if$bond[$y ][$x-1] =~ / /;
return $D{Right} if$bond[$y ][$x+1] =~ / /;
return $D{Up} if defined$bond[$y-1][$x  ] && $bond[$y-1][$x] =~ / /; return$D{DeadEnd}
}

sub move {
my($dir,$x,$y) = @_; fill($x,--$y), fill($x,--$y) if$dir == $D{Up}; fill($x,++$y), fill($x,++$y) if$dir == $D{Down}; fill(--$x,  $y), fill(--$x,  $y) if$dir == $D{Left}; fill(++$x,  $y), fill(++$x,  $y) if$dir == $D{Right};$x, $y } sub fill { my($x, $y) = @_;$bond[$y][$x] =~ s/ /$water/g } sub generate { our($prob) = shift || 0.5;
@bond = ();
our $sp = ' '; push @bond, ['│', ($sp, ' ') x ($grid-1),$sp, '│'],
['├', hx('┬'), h(), '┤'];
push @bond, ['│', vx(   ), $sp, '│'], ['├', hx('┼'), h(), '┤'] for 1..$grid-1;
push @bond, ['│', vx(   ), $sp, '│'], ['├', hx('┴'), h(), '┤'], ['│', ($sp, ' ') x ($grid-1),$sp, '│'];

sub hx { my($c)=@_; my @l; push @l, (h(),$c) for 1..$grid-1; return @l; } sub vx { my @l; push @l,$sp, v() for 1..$grid-1; return @l; } sub h { rand() <$prob ? $sp : '───' } sub v { rand() <$prob ? ' ' : '│'   }
}

print "Sample percolation at .6\n";
percolate(.6);
for my $row (@bond) { my$line = '';
$line .= join '',$_ for @$row; print "$line\n";
}

my $tests = 100; print "Doing$tests trials at each porosity:\n";
my @table;
for my $p (1 .. 10) {$p = $p/10; my$total = 0;
$total += percolate($p) for 1..$tests; printf "p = %0.1f: %0.2f\n",$p, $total /$tests
}


{{out}}

Sample percolation at .6
│▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒                          │
├───┬───┬───┬▒▒▒┬   ┬   ┬   ┬───┬   ┬───┤
│        ▒▒▒▒▒▒▒             │       │   │
├───┼───┼▒▒▒┼───┼───┼   ┼───┼───┼   ┼   ┤
│   │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒│         │   │   │
├───┼───┼───┼───┼▒▒▒┼▒▒▒┼   ┼───┼───┼───┤
│       │       │▒▒▒│▒▒▒▒▒▒▒             │
├───┼───┼   ┼───┼───┼───┼▒▒▒┼   ┼   ┼   ┤
│   │                ▒▒▒▒▒▒▒     │       │
├───┼───┼───┼   ┼   ┼▒▒▒┼───┼   ┼   ┼───┤
│       │           │▒▒▒            │   │
├───┼   ┼───┼   ┼───┼▒▒▒┼   ┼   ┼───┼   ┤
│   │            ▒▒▒▒▒▒▒│        │       │
├   ┼   ┼   ┼   ┼▒▒▒┼───┼   ┼───┼───┼   ┤
│       │        ▒▒▒│   │               │
├   ┼   ┼   ┼   ┼▒▒▒┼───┼   ┼   ┼───┼   ┤
│           │    ▒▒▒│               │   │
├───┼   ┼───┼   ┼▒▒▒┼   ┼   ┼   ┼   ┼   ┤
│   │           │▒▒▒        │   │   │   │
├───┼───┼   ┼   ┼▒▒▒┼───┼   ┼   ┼   ┼───┤
│           │    ▒▒▒│       │   │       │
├   ┴───┴   ┴   ┴▒▒▒┴   ┴───┴   ┴   ┴───┤
│                ▒▒▒                    │
Doing 100 trials at each porosity:
p = 0.1: 0.00
p = 0.2: 0.00
p = 0.3: 0.00
p = 0.4: 0.03
p = 0.5: 0.38
p = 0.6: 0.83
p = 0.7: 0.99
p = 0.8: 1.00
p = 0.9: 1.00
p = 1.0: 1.00


## Perl 6

{{works with|Rakudo|2017.02}} Starts "filling" from the top left. Fluid flow favours directions in Down, Left, Right, Up order. I interpreted p to be porosity, so small p mean low permeability, large p means high permeability.

my @bond;
my $grid = 10; my$geom = $grid - 1; my$water = '▒';

enum Direction <DeadEnd Up Right Down Left>;

say 'Sample percolation at .6';
percolate .6;
.join.say for @bond;
say "\n";

my $tests = 100; say "Doing$tests trials at each porosity:";
for .1, .2 ... 1 -> $p { printf "p = %0.1f: %0.2f\n",$p, (sum percolate($p) xx$tests) / $tests } sub percolate ($prob ) {
generate $prob; my @stack; my$current = [1;0];
$current.&fill; loop { if my$dir = direction( $current ) { @stack.push:$current;
$current = move$dir, $current } else { return 0 unless @stack;$current = @stack.pop
}
return 1 if $current[1] == +@bond - 1 } sub direction( [$x, $y] ) { ( Down if @bond[$y + 1][$x].contains: ' ' ) || ( Left if @bond[$y][$x - 1].contains: ' ' ) || ( Right if @bond[$y][$x + 1].contains: ' ' ) || ( Up if @bond[$y - 1][$x].defined && @bond[$y - 1][$x].contains: ' ' ) || DeadEnd } sub move ($dir, @cur ) {
my ( $x,$y ) = @cur;
given $dir { when Up { [$x,--$y].&fill xx 2 } when Down { [$x,++$y].&fill xx 2 } when Left { [--$x,$y].&fill xx 2 } when Right { [++$x,$y].&fill xx 2 } } [$x, $y] } sub fill ( [$x, $y] ) { @bond[$y;$x].=subst(' ',$water, :g) }
}

sub generate ( $prob = .5 ) { @bond = (); my$sp = '   ';
append @bond, [flat '│', ($sp, ' ') xx$geom, $sp, '│'], [flat '├', (h(), '┬') xx$geom, h(), '┤'];
append @bond, [flat '│', ($sp, v()) xx$geom, $sp, '│'], [flat '├', (h(), '┼') xx$geom, h(), '┤'] for ^$geom; append @bond, [flat '│', ($sp, v()) xx $geom,$sp, '│'],
[flat '├', (h(), '┴') xx $geom, h(), '┤'], [flat '│', ($sp, ' ') xx $geom,$sp, '│'];

sub h () { rand < $prob ??$sp !! '───' }
sub v () { rand < $prob ?? ' ' !! '│' } }  {{out}} Sample percolation at .6 │▒▒▒ │ ├▒▒▒┬ ┬───┬ ┬ ┬ ┬ ┬ ┬───┬ ┤ │▒▒▒▒▒▒▒ │ │ │ ├───┼▒▒▒┼ ┼ ┼ ┼ ┼ ┼───┼ ┼ ┤ │▒▒▒▒▒▒▒▒▒▒▒│ │ │ │ │ │ │ ├▒▒▒┼───┼▒▒▒┼ ┼───┼ ┼───┼ ┼ ┼ ┤ │▒▒▒│▒▒▒▒▒▒▒▒▒▒▒ │ │ │ ├▒▒▒┼───┼───┼▒▒▒┼ ┼ ┼───┼ ┼ ┼ ┤ │▒▒▒│ ▒▒▒│ │ │ │ │ ├───┼ ┼ ┼▒▒▒┼───┼ ┼ ┼ ┼ ┼───┤ │ │▒▒▒ │ │ ├ ┼───┼ ┼▒▒▒┼───┼───┼───┼───┼ ┼───┤ │ │▒▒▒│ │ ├───┼ ┼───┼▒▒▒┼───┼───┼───┼───┼ ┼───┤ │▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒ │ │ │ ├▒▒▒┼▒▒▒┼───┼▒▒▒┼───┼ ┼───┼ ┼ ┼ ┤ │▒▒▒│▒▒▒▒▒▒▒│▒▒▒▒▒▒▒│ │ ├▒▒▒┼───┼───┼───┼───┼───┼ ┼ ┼ ┼ ┤ │▒▒▒▒▒▒▒ │ │ │ │ ├▒▒▒┼▒▒▒┼───┼───┼ ┼───┼───┼ ┼ ┼ ┤ │▒▒▒│▒▒▒ │ │ │ ├───┴▒▒▒┴ ┴ ┴ ┴───┴ ┴ ┴ ┴───┤ │ ▒▒▒ │ Doing 100 trials at each porosity: p = 0.1: 0.00 p = 0.2: 0.00 p = 0.3: 0.00 p = 0.4: 0.05 p = 0.5: 0.42 p = 0.6: 0.92 p = 0.7: 1.00 p = 0.8: 1.00 p = 0.9: 1.00 p = 1.0: 1.00  ## Phix constant w = 10, h = 10 sequence wall = join(repeat("+",w+1),"---")&"\n", cell = join(repeat("|",w+1)," ")&"\n", grid procedure new_grid(atom p) grid = split(join(repeat(wall,h+1),cell),'\n') -- now knock down some walls for i=1 to length(grid)-1 do integer jstart = 5-mod(i,2)*3, jlimit = length(grid[i])-3 -- (ie 2..38 on odd lines, 5..37 on even) for j=jstart to jlimit by 4 do if rnd()>p then grid[i][j..j+2] = " " end if end for end for end procedure function percolate(integer x=0, y=0) if x=0 then for j=3 to length(grid[1])-2 by 4 do if grid[1][j]=' ' and percolate(1,j) then return true end if end for elsif grid[x][y]=' ' then grid[x][y] = '*' if (x=length(grid)-1) or ( grid[x+1][y]=' ' and percolate(x+1,y)) or (y>6 and grid[x][y-2]=' ' and percolate(x,y-4)) or (y<36 and grid[x][y+2]=' ' and percolate(x,y+4)) or (x>1 and grid[x-1][y]=' ' and percolate(x-1,y)) then return true end if end if return false end function constant LIM=1000 for p=0 to 10 do integer count = 0 for t=1 to LIM do new_grid(p/10) count += percolate() end for printf(1,"p=%.1f: %5.3f\n",{p/10,count/LIM}) end for puts(1,"sample grid for p=0.6:\n") new_grid(0.6) {} = percolate() puts(1,join(grid,'\n'))  {{out}}  p=0.0: 1.000 p=0.1: 1.000 p=0.2: 1.000 p=0.3: 0.997 p=0.4: 0.897 p=0.5: 0.434 p=0.6: 0.067 p=0.7: 0.003 p=0.8: 0.000 p=0.9: 0.000 p=1.0: 0.000 sample grid for p=0.6: +---+---+ * +---+ * + * +---+---+ * + * + | * * * | | * * | * | | * * | +---+---+ * + +---+ * + * +---+---+ * + | * * | * | | | * | * | * * * | +---+ * + * +---+---+---+ * +---+ * +---+ | | * | * | * | * | * * * * * | + + * + * + * + * + * +---+ * + * +---+ | | * * * * | * * | * * * | + + * + * +---+ * +---+ * +---+ * + * + | | * | * * * | * * | * * | * | +---+ * +---+ * +---+---+---+---+ * + * + | | * | | * * * * | * * | * | + +---+ +---+ * +---+---+---+---+ * + | | | | | * | | | * | + +---+---+ +---+---+---+---+---+---+ | | | | | | | | | | +---+---+---+ + +---+ + +---+---+ | | | | | | | | | + +---+ +---+---+ +---+---+---+---+ | | | | | | | | | | +---+---+ + + +---+---+---+---+ +  ## Python from collections import namedtuple from random import random from pprint import pprint as pp Grid = namedtuple('Grid', 'cell, hwall, vwall') M, N, t = 10, 10, 100 class PercolatedException(Exception): pass HVF = [(' .', ' _'), (':', '|'), (' ', '#')] # Horiz, vert, fill chars def newgrid(p): hwall = [[int(random() < p) for m in range(M)] for n in range(N+1)] vwall = [[(1 if m in (0, M) else int(random() < p)) for m in range(M+1)] for n in range(N)] cell = [[0 for m in range(M)] for n in range(N)] return Grid(cell, hwall, vwall) def pgrid(grid, percolated=None): cell, hwall, vwall = grid h, v, f = HVF for n in range(N): print(' ' + ''.join(h[hwall[n][m]] for m in range(M))) print('%i) ' % (n % 10) + ''.join(v[vwall[n][m]] + f[cell[n][m] if m < M else 0] for m in range(M+1))[:-1]) n = N print(' ' + ''.join(h[hwall[n][m]] for m in range(M))) if percolated: where = percolated.args[0][0] print('!) ' + ' ' * where + ' ' + f[1]) def pour_on_top(grid): cell, hwall, vwall = grid n = 0 try: for m in range(M): if not hwall[n][m]: flood_fill(m, n, cell, hwall, vwall) except PercolatedException as ex: return ex return None def flood_fill(m, n, cell, hwall, vwall): # fill cell cell[n][m] = 1 # bottom if n < N - 1 and not hwall[n + 1][m] and not cell[n+1][m]: flood_fill(m, n+1, cell, hwall, vwall) # THE bottom elif n == N - 1 and not hwall[n + 1][m]: raise PercolatedException((m, n+1)) # left if m and not vwall[n][m] and not cell[n][m - 1]: flood_fill(m-1, n, cell, hwall, vwall) # right if m < M - 1 and not vwall[n][m + 1] and not cell[n][m + 1]: flood_fill(m+1, n, cell, hwall, vwall) # top if n and not hwall[n][m] and not cell[n-1][m]: flood_fill(m, n-1, cell, hwall, vwall) if __name__ == '__main__': sample_printed = False pcount = {} for p10 in range(11): p = (10 - p10) / 10.0 # count down so sample print is interesting pcount[p] = 0 for tries in range(t): grid = newgrid(p) percolated = pour_on_top(grid) if percolated: pcount[p] += 1 if not sample_printed: print('\nSample percolating %i x %i grid' % (M, N)) pgrid(grid, percolated) sample_printed = True print('\n p: Fraction of %i tries that percolate through' % t ) pp({p:c/float(t) for p, c in pcount.items()})  {{out}} In the Ascii art, cells are either a space or a hash and are surrounded by either '_', '|' for intact walls and '.' and ':' for missing (leaky) walls. The bottom-most line starting '!)' shows where the fluid can drip out from. (The percolation stops when one route through the bottom is found). Sample percolating 10 x 10 grid _ _ . _ . _ _ . _ _ 0) | |#:#:#|#| | :#| | | _ _ . _ _ _ . . _ _ 1) | | |#:#| | | |#| : | _ _ _ . _ . . . . _ 2) | | |#:#| : | |#: | | _ _ _ _ . . _ . . . 3) | : : | | | : |#: | | _ _ . _ . . _ . _ _ 4) | : : : | | | |#: : | _ _ _ . _ _ _ . . _ 5) | : | | : | | :#| | | _ _ . . _ _ _ . _ . 6) | : | | : | |#:#:#| | _ . _ _ . _ _ _ . . 7) | : | : | : | | |#: | _ _ _ . . _ _ . . _ 8) | | : | | | |#:#:#: | _ _ _ . . . . _ _ . 9) | : : | : : :#: | : | . _ . _ . . . . _ _ !) # p: Fraction of 100 tries that percolate through {0.0: 1.0, 0.1: 1.0, 0.2: 1.0, 0.3: 1.0, 0.4: 0.9, 0.5: 0.47, 0.6: 0.06, 0.7: 0.0, 0.8: 0.0, 0.9: 0.0, 1.0: 0.0}  Note the abrupt cut-off in percolation at around p = 0.5 which is to be [http://mathworld.wolfram.com/PercolationThreshold.html expected]. ## Racket #lang racket (define has-left-wall? (lambda (x) (bitwise-bit-set? x 0))) (define has-right-wall? (lambda (x) (bitwise-bit-set? x 1))) (define has-top-wall? (lambda (x) (bitwise-bit-set? x 2))) (define has-bottom-wall? (lambda (x) (bitwise-bit-set? x 3))) (define has-fluid? (lambda (x) (bitwise-bit-set? x 4))) (define (walls->cell l? r? t? b?) (+ (if l? 1 0) (if r? 2 0) (if t? 4 0) (if b? 8 0))) (define (bonded-percol-grid M N p) (define rv (make-vector (* M N))) (for* ((idx (in-range (* M N)))) (define left-wall? (or (zero? (modulo idx M)) (has-right-wall? (vector-ref rv (sub1 idx))))) (define right-wall? (or (= (modulo idx M) (sub1 M)) (< (random) p))) (define top-wall? (if (< idx M) (< (random) p) (has-bottom-wall? (vector-ref rv (- idx M))))) (define bottom-wall? (< (random) p)) (define cell-value (walls->cell left-wall? right-wall? top-wall? bottom-wall?)) (vector-set! rv idx cell-value)) rv) (define (display-percol-grid M . vs) (define N (/ (vector-length (car vs)) M)) (define-syntax-rule (tab-eol m) (when (= m (sub1 M)) (printf "\t"))) (for ((n N)) (for* ((v vs) (m M)) (when (zero? m) (printf "+")) (printf (match (vector-ref v (+ (* n M) m)) ((? has-top-wall?) "-+") ((? has-fluid?) "#+") (else ".+"))) (tab-eol m)) (newline) (for* ((v vs) (m M)) (when (zero? m) (printf "|")) (printf (match (vector-ref v (+ (* n M) m)) ((and (? has-fluid?) (? has-right-wall?)) "#|") ((? has-right-wall?) ".|") ((? has-fluid?) "##") (else ".."))) (tab-eol m)) (newline)) (for* ((v vs) (m M)) (when (zero? m) (printf "+")) (printf (match (vector-ref v (+ (* (sub1 M) M) m)) ((? has-bottom-wall?) "-+") ((? has-fluid?) "#+") (else ".+"))) (tab-eol m)) (newline)) (define (find-bonded-grid-t/b-path M v) (define N (/ (vector-length v) M)) (define (flood-cell idx) (cond [(= (quotient idx M) N) #t] ; wootiments! [(has-fluid? (vector-ref v idx)) #f] ; been here [else (define cell (vector-ref v idx)) (vector-set! v idx (bitwise-ior cell 16)) (or (and (not (has-bottom-wall? cell)) (flood-cell (+ idx M))) (and (not (has-left-wall? cell)) (flood-cell (- idx 1))) (and (not (has-right-wall? cell)) (flood-cell (+ idx 1))) (and (not (has-top-wall? cell)) (>= idx M) ; not top row (flood-cell (- idx M))))])) (for/first ((m (in-range M)) #:unless (has-top-wall? (vector-ref v m)) #:when (flood-cell m)) #t)) (define t (make-parameter 1000)) (define (experiment p) (/ (for*/sum ((sample (in-range (t))) (v (in-value (bonded-percol-grid 10 10 p))) #:when (find-bonded-grid-t/b-path 10 v)) 1) (t))) (define (main) (for ((tenths (in-range 0 (add1 10)))) (define p (/ tenths 10)) (define e (experiment p)) (printf "proportion of grids that percolate p=~a : ~a (~a)~%" p e (real->decimal-string e 5)))) (module+ test (define (make/display/flood/display-bonded-grid M N p attempts (atmpt 1)) (define v (bonded-percol-grid M N p)) (define v+ (vector-copy v)) (cond [(or (find-bonded-grid-t/b-path M v+) (= attempts 0)) (define v* (vector-copy v+)) (define (flood-bonded-grid) (when (find-bonded-grid-t/b-path M v*) (flood-bonded-grid))) (flood-bonded-grid) (display-percol-grid M v v+ v*) (printf "After ~a attempt(s)~%~%" atmpt)] [else (make/display/flood/display-bonded-grid M N p (sub1 attempts) (add1 atmpt))])) (make/display/flood/display-bonded-grid 10 10 0 20) (make/display/flood/display-bonded-grid 10 10 .25 20) (make/display/flood/display-bonded-grid 10 10 .50 20) (make/display/flood/display-bonded-grid 10 10 .75 20000))  {{out}} Welcome to DrRacket, version 5.3.5 [3m]. Language: racket [custom]; memory limit: 1024 MB. +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ |...................| |##.................| |###################| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+#+#+#+#+#+#+#+ After 1 attempt(s) +.+-+-+.+.+.+-+.+.+.+ +#+-+-+.+.+.+-+.+.+.+ +#+-+-+#+#+#+-+#+#+#+ |...................| |##.................| |##..###############| +.+-+.+-+.+.+-+-+-+.+ +#+-+.+-+.+.+-+-+-+.+ +#+-+#+-+#+#+-+-+-+#+ |.................|.| |##...............|.| |##..##..####.....|#| +.+-+.+.+.+.+-+.+.+.+ +#+-+.+.+.+.+-+.+.+.+ +#+-+#+.+#+#+-+.+.+#+ |.............|.....| |##...........|.....| |######..#####|....#| +.+.+.+.+.+.+.+.+.+.+ +#+.+.+.+.+.+.+.+.+.+ +#+#+#+.+#+#+#+.+.+#+ |.....|...|.|.......| |##...|...|.|.......| |#####|..#|#|##....#| +.+.+.+.+.+.+.+-+-+.+ +#+.+.+.+.+.+.+-+-+.+ +#+#+#+#+#+#+#+-+-+#+ |.|.............|...| |#|.............|...| |#|############.|..#| +.+-+-+.+-+.+.+.+.+.+ +#+-+-+.+-+.+.+.+.+.+ +#+-+-+#+-+#+#+.+.+#+ |...................| |##.................| |##....##..####....#| +.+.+-+.+.+.+.+-+-+.+ +#+.+-+.+.+.+.+-+-+.+ +#+.+-+#+.+#+#+-+-+#+ |...|...|...........| |##.|...|...........| |##.|###|..####..###| +.+.+.+-+.+.+.+.+.+.+ +#+#+.+-+.+.+.+.+.+.+ +#+#+#+-+.+#+#+.+#+#+ |...|...|.........|.| |###|...|.........|.| |###|##.|..####..#|#| +-+.+.+-+-+.+.+.+.+-+ +-+#+.+-+-+.+.+.+.+-+ +-+#+#+-+-+#+#+.+#+-+ |.....|.........|...| |..##.|.........|...| |..###|....####.|###| +.+.+.+.+.+.+.+.+.+.+ +.+#+.+.+.+.+.+.+.+.+ +.+#+#+.+.+#+#+#+#+#+ |.........|.......|.| |..##.....|.......|.| |..####...|#######|#| +.+.+.+-+.+.+-+.+-+.+ +.+#+.+-+.+.+-+.+-+.+ +.+#+#+-+.+#+-+#+-+#+ After 1 attempt(s) +.+.+.+.+-+-+.+-+.+.+ +#+#+#+#+-+-+.+-+.+.+ +#+#+#+#+-+-+#+-+#+#+ |.........|.|.|...|.| |########.|.|.|...|.| |########.|.|#|###|#| +.+-+-+.+-+-+-+.+.+-+ +#+-+-+#+-+-+-+.+.+-+ +#+-+-+#+-+-+-+#+#+-+ |...|...|...|.|.|.|.| |###|..#|...|.|.|.|.| |###|..#|...|.|#|#|.| +-+-+.+.+.+.+-+.+-+.+ +-+-+.+#+#+.+-+.+-+.+ +-+-+.+#+#+.+-+#+-+.+ |.|.|.|...|.|.|.|...| |.|.|.|###|.|.|.|...| |.|.|.|###|.|.|#|...| +.+-+.+-+.+.+.+-+.+-+ +.+-+.+-+#+.+.+-+.+-+ +.+-+.+-+#+.+.+-+.+-+ |.|...|...|.|.....|.| |.|...|###|.|.....|.| |.|...|###|.|.....|.| +.+-+.+.+.+-+-+.+.+.+ +.+-+.+#+#+-+-+.+.+.+ +.+-+.+#+#+-+-+.+.+.+ |.|...|.|.....|.....| |.|...|#|####.|.....| |.|...|#|####.|.....| +-+.+-+.+-+.+-+.+-+-+ +-+.+-+#+-+#+-+#+-+-+ +-+.+-+#+-+#+-+#+-+-+ |.|.|.....|.....|...| |.|.|#####|#####|...| |.|.|#####|#####|...| +-+-+.+.+.+.+-+.+-+-+ +-+-+#+#+#+#+-+#+-+-+ +-+-+#+#+#+#+-+#+-+-+ |...|.|.....|.......| |...|#|#####|..##...| |...|#|#####|..##...| +-+-+-+-+-+-+-+.+-+-+ +-+-+-+-+-+-+-+#+-+-+ +-+-+-+-+-+-+-+#+-+-+ |.|...|.|.|.......|.| |.|...|.|.|######.|.| |.|...|.|.|######.|.| +.+-+-+-+.+.+-+.+.+.+ +.+-+-+-+.+#+-+#+.+.+ +.+-+-+-+.+#+-+#+.+.+ |.|...|.......|.|.|.| |.|...|....##.|#|.|.| |.|...|....##.|#|.|.| +.+.+-+.+.+.+-+-+-+-+ +.+.+-+.+.+#+-+-+-+-+ +.+.+-+.+.+#+-+-+-+-+ |.|.........|.....|.| |.|........#|.....|.| |.|........#|.....|.| +-+.+-+-+-+.+.+.+-+.+ +-+.+-+-+-+#+.+.+-+.+ +-+.+-+-+-+#+.+.+-+.+ After 2 attempt(s) +-+-+-+-+-+-+.+-+-+.+ +-+-+-+-+-+-+#+-+-+.+ +-+-+-+-+-+-+#+-+-+#+ |.|.|...|.|.|.|.|...| |.|.|...|.|.|#|.|...| |.|.|...|.|.|#|.|###| +-+-+-+-+-+-+.+-+-+-+ +-+-+-+-+-+-+#+-+-+-+ +-+-+-+-+-+-+#+-+-+-+ |.|.|.|...|.|...|.|.| |.|.|.|...|.|##.|.|.| |.|.|.|...|.|##.|.|.| +.+.+.+.+.+-+.+-+-+.+ +.+.+.+.+.+-+#+-+-+.+ +.+.+.+.+.+-+#+-+-+.+ |.|.|.|.|...|.|...|.| |.|.|.|.|...|#|...|.| |.|.|.|.|...|#|...|.| +.+-+.+-+-+-+.+-+.+.+ +.+-+.+-+-+-+#+-+.+.+ +.+-+.+-+-+-+#+-+.+.+ |...|...|.|.|...|.|.| |...|...|.|.|###|.|.| |...|...|.|.|###|.|.| +-+-+-+-+-+-+-+.+-+-+ +-+-+-+-+-+-+-+#+-+-+ +-+-+-+-+-+-+-+#+-+-+ |.|.......|.....|.|.| |.|.......|#####|.|.| |.|.......|#####|.|.| +.+-+-+-+.+.+-+-+-+-+ +.+-+-+-+.+#+-+-+-+-+ +.+-+-+-+.+#+-+-+-+-+ |.|.|.|.|.|.|.|.....| |.|.|.|.|.|#|.|.....| |.|.|.|.|.|#|.|.....| +-+-+-+-+-+.+.+-+.+-+ +-+-+-+-+-+#+.+-+.+-+ +-+-+-+-+-+#+.+-+.+-+ |...|.|.|.|.|.|.|.|.| |...|.|.|.|#|.|.|.|.| |...|.|.|.|#|.|.|.|.| +.+.+.+-+-+.+.+-+.+-+ +.+.+.+-+-+#+#+-+.+-+ +.+.+.+-+-+#+#+-+.+-+ |.|.|.|.|.|...|.|...| |.|.|.|.|.|###|.|...| |.|.|.|.|.|###|.|...| +-+-+-+-+-+-+.+.+.+-+ +-+-+-+-+-+-+#+.+.+-+ +-+-+-+-+-+-+#+.+.+-+ |.|.|.|.|.|...|...|.| |.|.|.|.|.|###|...|.| |.|.|.|.|.|###|...|.| +-+-+.+-+-+.+-+-+-+.+ +-+-+.+-+-+#+-+-+-+.+ +-+-+.+-+-+#+-+-+-+.+ |.|.|.|...|...|.|...| |.|.|.|...|###|.|...| |.|.|.|...|###|.|...| +-+-+.+-+.+-+.+.+.+-+ +-+-+.+-+.+-+#+.+.+-+ +-+-+.+-+.+-+#+.+.+-+ After 4611 attempt(s) > (main) proportion of grids that percolate p=0 : 1 (1.00000) proportion of grids that percolate p=1/10 : 1 (1.00000) proportion of grids that percolate p=1/5 : 1 (1.00000) proportion of grids that percolate p=3/10 : 199/200 (0.99500) proportion of grids that percolate p=2/5 : 179/200 (0.89500) proportion of grids that percolate p=1/2 : 451/1000 (0.45100) proportion of grids that percolate p=3/5 : 29/500 (0.05800) proportion of grids that percolate p=7/10 : 1/1000 (0.00100) proportion of grids that percolate p=4/5 : 0 (0.00000) proportion of grids that percolate p=9/10 : 0 (0.00000) proportion of grids that percolate p=1 : 0 (0.00000)  ## Swift {{trans|C}} let randMax = 32767.0 let filled = 1 let rightWall = 2 let bottomWall = 4 final class Percolate { let height: Int let width: Int private var grid: [Int] private var end: Int init(height: Int, width: Int) { self.height = height self.width = width self.end = width self.grid = [Int](repeating: 0, count: width * (height + 2)) } private func fill(at p: Int) -> Bool { guard grid[p] & filled == 0 else { return false } grid[p] |= filled guard p < end else { return true } return (((grid[p + 0] & bottomWall) == 0) && fill(at: p + width)) || (((grid[p + 0] & rightWall) == 0) && fill(at: p + 1)) || (((grid[p - 1] & rightWall) == 0) && fill(at: p - 1)) || (((grid[p - width] & bottomWall) == 0) && fill(at: p - width)) } func makeGrid(porosity p: Double) { grid = [Int](repeating: 0, count: width * (height + 2)) end = width let thresh = Int(randMax * p) for i in 0..<width { grid[i] = bottomWall | rightWall } for _ in 0..<height { for _ in stride(from: width - 1, through: 1, by: -1) { let r1 = Int.random(in: 0..<Int(randMax)+1) let r2 = Int.random(in: 0..<Int(randMax)+1) grid[end] = (r1 < thresh ? bottomWall : 0) | (r2 < thresh ? rightWall : 0) end += 1 } let r3 = Int.random(in: 0..<Int(randMax)+1) grid[end] = rightWall | (r3 < thresh ? bottomWall : 0) end += 1 } } @discardableResult func percolate() -> Bool { var i = 0 while i < width && !fill(at: width + i) { i += 1 } return i < width } func showGrid() { for _ in 0..<width { print("+--", terminator: "") } print("+") for i in 0..<height { print(i == height ? " " : "|", terminator: "") for j in 0..<width { print(grid[i * width + j + width] & filled != 0 ? "[]" : " ", terminator: "") print(grid[i * width + j + width] & rightWall != 0 ? "|" : " ", terminator: "") } print() guard i != height else { return } for j in 0..<width { print(grid[i * width + j + width] & bottomWall != 0 ? "+--" : "+ ", terminator: "") } print("+") } } } let p = Percolate(height: 10, width: 10) p.makeGrid(porosity: 0.5) p.percolate() p.showGrid() print("Running \(p.height) x \(p.width) grid 10,000 times for each porosity") for factor in 1...10 { var count = 0 let porosity = Double(factor) / 10.0 for _ in 0..<10_000 { p.makeGrid(porosity: porosity) if p.percolate() { count += 1 } } print("p = \(porosity): \(Double(count) / 10_000.0)") }  {{out}} +--+--+--+--+--+--+--+--+--+--+ |[]| | | | | | | + + +--+--+ + +--+ + + + |[] [] | | | | +--+ +--+--+ +--+--+ +--+ + | [] [] []| | | | + +--+--+ + +--+--+ + + + | [] []| | | +--+--+ +--+ + + + +--+ + | [] [] | | | | + +--+--+ +--+--+--+--+ +--+ | | | |[] | | | + + +--+ +--+--+--+--+--+--+ | | |[] [] [] | | +--+--+--+--+--+ + +--+--+ + | | | |[]| | | | + + + + +--+ +--+ + +--+ | | | | [] []| | | | +--+--+--+--+ +--+--+--+--+ + | | | [] | | | +--+--+ +--+ +--+ +--+--+ + Running 10 x 10 grid 10,000 times for each porosity p = 0.1: 1.0 p = 0.2: 1.0 p = 0.3: 0.9968 p = 0.4: 0.9125 p = 0.5: 0.4959 p = 0.6: 0.0858 p = 0.7: 0.004 p = 0.8: 0.0 p = 0.9: 0.0 p = 1.0: 0.0  ## Tcl {{works with|Tcl|8.6}} {{trans|Python}} package require Tcl 8.6 # Structure the bond percolation system as a class oo::class create BondPercolation { variable hwall vwall cells M N constructor {width height probability} { set M$height
set N $width for {set i 0} {$i <= $height} {incr i} { for {set j 0;set walls {}} {$j < $width} {incr j} { lappend walls [expr {rand() <$probability}]
}
lappend hwall $walls } for {set i 0} {$i <= $height} {incr i} { for {set j 0;set walls {}} {$j <= $width} {incr j} { lappend walls [expr {$j==0 || $j==$width || rand() < $probability}] } lappend vwall$walls
}
set cells [lrepeat $height [lrepeat$width 0]]
}

method print {{percolated ""}} {
set nw [string length $M] set grid$cells
if {$percolated ne ""} { lappend grid [lrepeat$N 0]
lset grid end $percolated 1 } foreach hws$hwall vws [lrange $vwall 0 end-1] r$grid {
incr row
puts -nonewline [string repeat " " [expr {$nw+2}]] foreach w$hws {
puts -nonewline [if {$w} {subst "+-"} {subst "+ "}] } puts "+" puts -nonewline [format "%-*s" [expr {$nw+2}] [expr {
$row>$M ? $percolated eq "" ? " " : ">" : "$row)"
}]]
foreach v $vws c$r {
puts -nonewline [if {$v==1} {subst "|"} {subst " "}] puts -nonewline [if {$c==1} {subst "#"} {subst " "}]
}
puts ""
}
}

method percolate {} {
try {
for {set i 0} {$i <$N} {incr i} {
if {![lindex $hwall 0$i]} {
my FloodFill $i 0 } } return "" } trap PERCOLATED n { return$n
}
}
method FloodFill {x y} {
# fill cell
lset cells $y$x 1
# bottom
if {![lindex $hwall [expr {$y+1}] $x]} { if {$y == $N-1} { # THE bottom throw PERCOLATED$x
}
if {$y <$N-1 && ![lindex $cells [expr {$y+1}] $x]} { my FloodFill$x [expr {$y+1}] } } # left if {![lindex$vwall $y$x] && ![lindex $cells$y [expr {$x-1}]]} { my FloodFill [expr {$x-1}] $y } # right if {![lindex$vwall $y [expr {$x+1}]] && ![lindex $cells$y [expr {$x+1}]]} { my FloodFill [expr {$x+1}] $y } # top if {$y>0 && ![lindex $hwall$y $x] && ![lindex$cells [expr {$y-1}]$x]} {
my FloodFill $x [expr {$y-1}]
}
}
}

# Demonstrate one run
puts "Sample percolation, 10x10 p=0.5"
BondPercolation create bp 10 10 0.5
bp print [bp percolate]
bp destroy
puts ""

# Collect some aggregate statistics
apply {{} {
puts "Percentage of tries that percolate, varying p"
set tries 100
for {set pint 0} {$pint <= 10} {incr pint} { set p [expr {$pint * 0.1}]
set tot 0
for {set i 0} {$i <$tries} {incr i} {
set bp [BondPercolation new 10 10 $p] if {[$bp percolate] ne ""} {
incr tot
}
$bp destroy } puts [format "p=%.2f: %2.1f%%"$p [expr {$tot*100./$tries}]]
}
}}


{{out}}


Sample percolation, 10x10 p=0.5
+ + +-+-+-+ +-+ +-+ +
1)  |#  |   |   |   |   |
+ +-+ + + +-+ + + +-+
2)  |#|       | |     | |
+ + +-+ +-+ +-+ + +-+
3)  |# # #|# # #| | |   |
+ +-+ + +-+ +-+ +-+ +
4)  |#|# # #| |#  |     |
+-+ + + +-+ +-+-+ +-+
5)  |# # # #| |#  |   | |
+-+-+-+-+ + + + +-+-+
6)  | |     | |#|   |   |
+-+-+-+-+-+ + +-+-+ +
7)  | | | |   |#      | |
+ +-+ +-+-+ +-+ +-+ +
8)  |       |  #    |   |
+ +-+-+ +-+ + + + + +
9)  |          #        |
+ + +-+-+ + +-+-+ + +
10) |   | |    #  | |   |
+ + + + + + +-+ +-+ +
>              #

Percentage of tries that percolate, varying p
p=0.00: 100.0%
p=0.10: 100.0%
p=0.20: 100.0%
p=0.30: 100.0%
p=0.40: 86.0%
p=0.50: 50.0%
p=0.60: 6.0%
p=0.70: 0.0%
p=0.80: 0.0%
p=0.90: 0.0%
p=1.00: 0.0%



## zkl

{{trans|C}}

// cell states
const FILLED=1; // and odd
const RWALL =2; // right wall
const BWALL =4; // bottom wall
fcn P(p,wall){ (0.0).random(1)<p and wall or 0 }

fcn makeGrid(m,n,p){
// Allocate two addition rows to avoid checking bounds.
// Bottom row is also required by drippage
grid:=Data(m*(n+2));
do(m){ grid.write(BWALL + RWALL); } // grid is topped with walls
do(n){
do(m-1){ grid.write( P(p,BWALL) + P(p,RWALL) ) }
grid.write(RWALL + P(p,BWALL));  // right border is all right wall, as is left border
}
do(m){ grid.write(0); } // for drips off the bottom of grid
grid
}
fcn show(grid,m,n){ n+=1;
println("+--"*m,"+");
foreach i in ([1..n]){ y:=i*m;
print(i==n and " " or "|"); // bottom row is special, otherwise always have left wall
foreach j in (m){ c:=grid[y + j];
print(c.bitAnd(FILLED) and "**" or "  ", c.bitAnd(RWALL)and"|"or" ");
}
println();

if(i==n) return();  // nothing under the bottom row

foreach j in (m){ print((grid[y + j].bitAnd(BWALL)) and "+--" or "+  "); }
println("+");
}
}
fcn fill(grid,x,m){
if(grid[x].isOdd) return(False); // aka .bitAnd(FILLED) aka already been here
grid[x]+=FILLED;
if(x+m>=grid.len()) return(True); // success: reached bottom row
return(( not grid[x]    .bitAnd(BWALL) and fill(grid,x + m,m) ) or // down
( not grid[x]    .bitAnd(RWALL) and fill(grid,x + 1,m) ) or // right
( not grid[x - 1].bitAnd(RWALL) and fill(grid,x - 1,m) ) or // left
( not grid[x - m].bitAnd(BWALL) and fill(grid,x - m,m) ));  // up
}
fcn percolate(grid,m){
i:=0; while(i<m and not fill(grid,i+m,m)){ i+=1; }  // pour juice on top row
return(i<m);  // percolated through the grid?
}

grid:=makeGrid(10,10,0.40);
println("Did liquid percolate: ",percolate(grid,10)); show(grid,10,10);

println("Running 10,000 tests for each case:");
foreach p in ([0.0 .. 1.0, 0.1]){
cnt:=0.0; do(10000){ cnt+=percolate(makeGrid(10,10,p),10); }
"p=%.1f:  %.4f".fmt(p, cnt/10000).println();
}


{{out}}


Did liquid percolate: True
+--+--+--+--+--+--+--+--+--+--+
|** **      |              |  |
+--+  +--+--+  +  +  +  +  +  +
|   **|  |        |        |  |
+  +  +  +--+  +--+--+  +--+--+
|   ** **      |              |
+--+--+  +  +  +  +--+  +  +--+
|     |**|  |        |        |
+  +  +  +  +--+  +  +--+  +  +
|      ** **|  |** **|     |  |
+  +--+--+  +--+  +  +--+  +  +
|     |  |**|  |**|** **      |
+  +  +  +  +--+  +--+  +  +  +
|     |  |** ** ** **|**      |
+--+--+--+--+  +--+--+  +--+--+
|  |     |** **|      **   |  |
+  +  +--+  +  +  +  +  +--+--+
|        |** **|     |**|  |  |
+  +--+  +--+--+--+--+  +  +  +
|              |  |   **|     |
+  +  +  +  +  +  +--+  +  +  +
**
Running 10,000 tests for each case:
p=0.0:  1.0000
p=0.1:  1.0000
p=0.2:  1.0000
p=0.3:  0.9978
p=0.4:  0.9163
p=0.5:  0.5017
p=0.6:  0.0890
p=0.7:  0.0033
p=0.8:  0.0000
p=0.9:  0.0000
p=1.0:  0.0000