mulRow(index, value) {
                util.checkRowIndex(this, index);
                for (var i = 0; i < this.columns; i++) {
                    this.set(index, i, this.get(index, i) * value);
                }
                return this;
            }
Multiplies the values of a row with a scalar
@param {number} index - Row index
@param {number} value
@return {Matrix} this