Resistor mesh: Difference between revisions
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m (→{{header|REXX}}: reverted to faster IF comparison.) |
(→{{header|Haskell}}: Added Haskell solution) |
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</lang>
=={{header|Haskell}}==
Translation of Octave program. All mutations are expressed as monoidal operations.
<lang haskell>{-# LANGUAGE ParallelListComp #-}
import Numeric.LinearAlgebra (linearSolve, toDense, (!), flatten)
import Data.Monoid ((<>), Sum(..))
rMesh n (ar, ac) (br, bc)
| n < 2 = Nothing
| any (\x -> x < 1 || x > n) [ar, ac, br, bc] = Nothing
| otherwise = between a b <$> voltage
where
a = (ac - 1) + n*(ar - 1)
b = (bc - 1) + n*(br - 1)
between x y v = abs (v ! a - v ! b)
voltage = flatten <$> linearSolve matrixG current
matrixG = toDense $ concat [ element row col node
| row <- [1..n], col <- [1..n]
| node <- [0..] ]
element row col node =
let (Sum c, elements) =
(Sum 1, [((node, node-n), -1)]) `when` (row > 1) <>
(Sum 1, [((node, node+n), -1)]) `when` (row < n) <>
(Sum 1, [((node, node-1), -1)]) `when` (col > 1) <>
(Sum 1, [((node, node+1), -1)]) `when` (col < n)
in [((node, node), c)] <> elements
x `when` p = if p then x else mempty
current = toDense [ ((a, 0), -1) , ((b, 0), 1) , ((n^2-1, 0), 0) ]</lang>
{{Out}}
λ> rMesh 10 (2,2) (7,8)
Just 1.6089912417307304
=={{header|J}}==
|