mathjs/src/function/algebra/sparse/csIpvec.js

/**
 * Permutes a vector; x = P'b. In MATLAB notation, x(p)=b.
 *
 * @param {Array} p           The permutation vector of length n. null value denotes identity
 * @param {Array} b           The input vector
 *
 * @return {Array}            The output vector x = P'b
 */
export function csIpvec (p, b) {
  // vars
  let k
  const n = b.length
  const x = []
  // check permutation vector was provided, p = null denotes identity
  if (p) {
    // loop vector
    for (k = 0; k < n; k++) {
      // apply permutation
      x[p[k]] = b[k]
    }
  } else {
    // loop vector
    for (k = 0; k < n; k++) {
      // x[i] = b[i]
      x[k] = b[k]
    }
  }
  return x
}