62 lines
1.5 KiB
Kotlin
62 lines
1.5 KiB
Kotlin
// version 1.1.4-3
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typealias List2D<T> = List<List<T>>
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const val S = 10
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class Node(var v: Double, var fixed: Int)
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fun setBoundary(m: List2D<Node>) {
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m[1][1].v = 1.0; m[1][1].fixed = 1
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m[6][7].v = -1.0; m[6][7].fixed = -1
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}
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fun calcDiff(m: List2D<Node>, d: List2D<Node>, w: Int, h: Int): Double {
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var total = 0.0
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for (i in 0 until h) {
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for (j in 0 until w) {
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var v = 0.0
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var n = 0
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if (i > 0) { v += m[i - 1][j].v; n++ }
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if (j > 0) { v += m[i][j - 1].v; n++ }
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if (i + 1 < h) { v += m[i + 1][j].v; n++ }
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if (j + 1 < w) { v += m[i][j + 1].v; n++ }
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v = m[i][j].v - v / n
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d[i][j].v = v
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if (m[i][j].fixed == 0) total += v * v
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}
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}
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return total
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}
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fun iter(m: List2D<Node>, w: Int, h: Int): Double {
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val d = List(h) { List(w) { Node(0.0, 0) } }
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val cur = DoubleArray(3)
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var diff = 1e10
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while (diff > 1e-24) {
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setBoundary(m)
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diff = calcDiff(m, d, w, h)
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for (i in 0 until h) {
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for (j in 0 until w) m[i][j].v -= d[i][j].v
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}
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}
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for (i in 0 until h) {
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for (j in 0 until w) {
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var k = 0
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if (i != 0) k++
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if (j != 0) k++
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if (i < h - 1) k++
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if (j < w - 1) k++
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cur[m[i][j].fixed + 1] += d[i][j].v * k
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}
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}
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return (cur[2] - cur[0]) / 2.0
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}
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fun main(args: Array<String>) {
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val mesh = List(S) { List(S) { Node(0.0, 0) } }
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val r = 2.0 / iter(mesh, S, S)
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println("R = $r")
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}
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