71 lines
1.7 KiB
JavaScript
71 lines
1.7 KiB
JavaScript
// Copyright (c) 2006-2024, Timothy A. Davis, All Rights Reserved.
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// SPDX-License-Identifier: LGPL-2.1+
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// https://github.com/DrTimothyAldenDavis/SuiteSparse/tree/dev/CSparse/Source
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/**
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* Computes the elimination tree of Matrix A (using triu(A)) or the
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* elimination tree of A'A without forming A'A.
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*
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* @param {Matrix} a The A Matrix
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* @param {boolean} ata A value of true the function computes the etree of A'A
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*/
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export function csEtree(a, ata) {
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// check inputs
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if (!a) {
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return null;
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}
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// a arrays
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var aindex = a._index;
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var aptr = a._ptr;
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var asize = a._size;
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// rows & columns
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var m = asize[0];
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var n = asize[1];
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// allocate result
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var parent = []; // (n)
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// allocate workspace
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var w = []; // (n + (ata ? m : 0))
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var ancestor = 0; // first n entries in w
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var prev = n; // last m entries (ata = true)
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var i, inext;
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// check we are calculating A'A
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if (ata) {
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// initialize workspace
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for (i = 0; i < m; i++) {
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w[prev + i] = -1;
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}
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}
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// loop columns
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for (var k = 0; k < n; k++) {
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// node k has no parent yet
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parent[k] = -1;
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// nor does k have an ancestor
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w[ancestor + k] = -1;
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// values in column k
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for (var p0 = aptr[k], p1 = aptr[k + 1], p = p0; p < p1; p++) {
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// row
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var r = aindex[p];
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// node
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i = ata ? w[prev + r] : r;
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// traverse from i to k
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for (; i !== -1 && i < k; i = inext) {
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// inext = ancestor of i
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inext = w[ancestor + i];
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// path compression
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w[ancestor + i] = k;
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// check no anc., parent is k
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if (inext === -1) {
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parent[i] = k;
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}
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}
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if (ata) {
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w[prev + r] = k;
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}
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}
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}
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return parent;
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} |