mathjs/lib/esm/function/algebra/sparse/csReach.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

// Copyright (c) 2006-2024, Timothy A. Davis, All Rights Reserved.
// SPDX-License-Identifier: LGPL-2.1+
// https://github.com/DrTimothyAldenDavis/SuiteSparse/tree/dev/CSparse/Source

import { csMarked } from './csMarked.js';
import { csMark } from './csMark.js';
import { csDfs } from './csDfs.js';

/**
 * The csReach function computes X = Reach(B), where B is the nonzero pattern of the n-by-1
 * sparse column of vector b. The function returns the set of nodes reachable from any node in B. The
 * nonzero pattern xi of the solution x to the sparse linear system Lx=b is given by X=Reach(B).
 *
 * @param {Matrix}  g               The G matrix
 * @param {Matrix}  b               The B matrix
 * @param {Number}  k               The kth column in B
 * @param {Array}   xi              The nonzero pattern xi[top] .. xi[n - 1], an array of size = 2 * n
 *                                  The first n entries is the nonzero pattern, the last n entries is the stack
 * @param {Array}   pinv            The inverse row permutation vector
 *
 * @return {Number}                 The index for the nonzero pattern
 */
export function csReach(g, b, k, xi, pinv) {
  // g arrays
  var gptr = g._ptr;
  var gsize = g._size;
  // b arrays
  var bindex = b._index;
  var bptr = b._ptr;
  // columns
  var n = gsize[1];
  // vars
  var p, p0, p1;
  // initialize top
  var top = n;
  // loop column indeces in B
  for (p0 = bptr[k], p1 = bptr[k + 1], p = p0; p < p1; p++) {
    // node i
    var i = bindex[p];
    // check node i is marked
    if (!csMarked(gptr, i)) {
      // start a dfs at unmarked node i
      top = csDfs(i, g, top, xi, pinv);
    }
  }
  // loop columns from top -> n - 1
  for (p = top; p < n; p++) {
    // restore G
    csMark(gptr, xi[p]);
  }
  return top;
}