# Percolation/Site percolation

``````class Percolate {

has block = '▒'
has water = '+'
has pore  = ' '
has grid  = 15
has site  = []

enum <DeadEnd, Up, Right, Down, Left>

method direction(x, y) {
((site[y + 1][x] == pore) && Down ) ||
((site[y][x - 1] == pore) && Left ) ||
((site[y][x + 1] == pore) && Right) ||
((site[y - 1][x] == pore) && Up   ) ||
DeadEnd
}

method move(dir, x, y) {
given (dir) {
when (Up)    { site[--y][x] = water }
when (Down)  { site[++y][x] = water }
when (Left)  { site[y][--x] = water }
when (Right) { site[y][++x] = water }
}
return (x, y)
}

method percolate (prob  = 0.6) {
site[0] = grid.of(pore)
site[grid + 1] = grid.of(pore)

for x = ^grid, y = 1..grid {
site[y][x] = (1.rand < prob ? pore : block)
}

site[0][0] = water

var stack = []
var (x, y) = (0, 0)

loop {
if (var dir = self.direction(x, y)) {
stack << [x, y]
(x,y) = self.move(dir, x, y)
}
else {
stack || return 0
(x,y) = stack.pop...
}
return 1 if (y > grid)
}
}
}

var obj = Percolate()
say 'Sample percolation at 0.6'
obj.percolate(0.6)
obj.site.each { .join.say }
say ''

var tests = 100
say "Doing #{tests} trials at each porosity:"
for p in (0.1..1 `by` 0.1) {
printf("p = %0.1f: %0.3f\n", p, tests.of { obj.percolate(p) }.sum / tests)
}
``````

#### Output:

``````Sample percolation at 0.6
+
+    ▒▒▒  ▒ ▒▒
+  ▒  ▒   ▒ ▒
++++  ▒  ▒    ▒
▒+▒+++++    ▒ ▒
▒ ▒▒▒▒+
▒▒ ▒ ▒ +      ▒
▒     ▒+++ ▒  ▒
▒ ▒ ▒+▒+  ▒
▒ ▒    ▒ + ▒  ▒
▒   ▒ +++   ▒▒
▒▒▒ ▒▒▒+▒+▒ ▒ ▒
▒   ▒▒ + ▒    ▒
▒▒  ▒▒+++  ▒ ▒
▒ ▒▒+
▒   ▒ ▒  +
+

Doing 100 trials at each porosity:
p = 0.1: 0.000
p = 0.2: 0.000
p = 0.3: 0.000
p = 0.4: 0.020
p = 0.5: 0.090
p = 0.6: 0.570
p = 0.7: 0.930
p = 0.8: 1.000
p = 0.9: 1.000
p = 1.0: 1.000
``````