function _permute (A, pinv, q) {
    // matrix arrays
    const values = A._values
    const index = A._index
    const ptr = A._ptr
    const size = A._size
    // columns
    const n = size[1]
    // c arrays
    const cvalues = []
    const cindex = []
    const cptr = []
    // loop columns
    for (let k = 0; k < n; k++) {
      cptr[k] = cindex.length
      // column in C
      const j = q ? (q[k]) : k
      // values in column j
      for (let t = ptr[j]; t < ptr[j + 1]; t++) {
        cvalues.push(values[t])
        cindex.push(pinv ? (pinv[index[t]]) : index[t])
      }
    }
    cptr[n] = cindex.length
    // return matrix
    return new math.SparseMatrix({
      values: cvalues,
      index: cindex,
      ptr: cptr,
      size,
      datatype: A._datatype
    })
  }
C = A(p,q) where p is the row permutation vector and q the column permutation vector.