Resistor mesh: Difference between revisions
Added Kotlin
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One advantage of this formulation is that it is easy to generalize to non-constant resistance.
If we have a vector <code>y</code> of admittance (1/resistance) values on each resistor, then one simply replaces <code>D' * D</code> with <code>D' * spdiagm(y) * D</code>.
=={{header|Kotlin}}==
{{trans|C}}
<lang scala>// version 1.1.4-3
typealias List2D<T> = List<List<T>>
const val S = 10
class Node(var v: Double, var fixed: Int)
fun setBoundary(m: List2D<Node>) {
m[1][1].v = 1.0; m[1][1].fixed = 1
m[6][7].v = -1.0; m[6][7].fixed = -1
}
fun calcDiff(m: List2D<Node>, d: List2D<Node>, w: Int, h: Int): Double {
var total = 0.0
for (i in 0 until h) {
for (j in 0 until w) {
var v = 0.0
var n = 0
if (i > 0) { v += m[i - 1][j].v; n++ }
if (j > 0) { v += m[i][j - 1].v; n++ }
if (i + 1 < h) { v += m[i + 1][j].v; n++ }
if (j + 1 < w) { v += m[i][j + 1].v; n++ }
v = m[i][j].v - v / n
d[i][j].v = v
if (m[i][j].fixed == 0) total += v * v
}
}
return total
}
fun iter(m: List2D<Node>, w: Int, h: Int): Double {
val d = List(h) { List(w) { Node(0.0, 0) } }
val cur = DoubleArray(3)
var diff = 1e10
while (diff > 1e-24) {
setBoundary(m)
diff = calcDiff(m, d, w, h)
for (i in 0 until h) {
for (j in 0 until w) m[i][j].v -= d[i][j].v
}
}
for (i in 0 until h) {
for (j in 0 until w) {
var k = 0
if (i != 0) k++
if (j != 0) k++
if (i < h - 1) k++
if (j < w - 1) k++
cur[m[i][j].fixed + 1] += d[i][j].v * k
}
}
return (cur[2] - cur[0]) / 2.0
}
fun main(args: Array<String>) {
val mesh = List(S) { List(S) { Node(0.0, 0) } }
val r = 2.0 / iter(mesh, S, S)
println("R = $r")
}</lang>
{{out}}
<pre>
R = 1.608991241729889
</pre>
=={{header|Maxima}}==
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