@rayyamhk/matrix/lib/core/properties/trace.js

A professional, comprehensive and high-performance library for you to manipulate matrices.

"use strict";

var _require = require('../../Error'),
    INVALID_SQUARE_MATRIX = _require.INVALID_SQUARE_MATRIX;
/**
 * Calculates the trace of any square Matrix,
 * which is the sum of all entries on the main diagonal.<br><br>
 * 
 * The trace is cached.
 * @memberof Matrix
 * @instance
 * @returns {number} The trace of the square Matrix.
 */


function trace() {
  var isSquare = this._isSquare !== undefined ? this._isSquare : this.isSquare();

  if (!isSquare) {
    throw new Error(INVALID_SQUARE_MATRIX);
  }

  if (this._trace !== undefined) {
    return this._trace;
  }

  var A = this._matrix;
  var size = A.length;
  var tr = 0;

  for (var i = 0; i < size; i++) {
    tr += A[i][i];
  }

  this._trace = tr;
  return tr;
}

;
module.exports = trace;