53 lines
1.2 KiB
JavaScript
53 lines
1.2 KiB
JavaScript
((() => {
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'use strict';
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// matrixMultiply :: Num a => [[a]] -> [[a]] -> [[a]]
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const matrixMultiply = (a, b) => {
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const bCols = transpose(b);
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return a.map(aRow => bCols.map(bCol => dotProduct(aRow, bCol)));
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}
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// dotProduct :: Num a => [[a]] -> [[a]] -> [[a]]
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const dotProduct = (xs, ys) => sum(zipWith(product, xs, ys));
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// GENERIC
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// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
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const zipWith = (f, xs, ys) =>
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xs.length === ys.length ? (
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xs.map((x, i) => f(x, ys[i]))
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) : undefined;
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// transpose :: [[a]] -> [[a]]
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const transpose = xs =>
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xs[0].map((_, iCol) => xs.map(row => row[iCol]));
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// sum :: (Num a) => [a] -> a
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const sum = xs =>
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xs.reduce((a, x) => a + x, 0);
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// product :: Num a => a -> a -> a
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const product = (a, b) => a * b;
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// TEST
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return matrixMultiply(
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[
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[-1, 1, 4],
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[6, -4, 2],
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[-3, 5, 0],
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[3, 7, -2]
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],
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[
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[-1, 1, 4, 8],
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[6, 9, 10, 2],
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[11, -4, 5, -3]
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]
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);
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// --> [[51, -8, 26, -18], [-8, -38, -6, 34],
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// [33, 42, 38, -14], [17, 74, 72, 44]]
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}))();
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