static rand(rows, columns, rng) {
                if (rng === undefined) rng = Math.random;
                var matrix = this.empty(rows, columns);
                for (var i = 0; i < rows; i++) {
                    for (var j = 0; j < columns; j++) {
                        matrix.set(i, j, rng());
                    }
                }
                return matrix;
            }
Creates a matrix with the given dimensions. Values will be randomly set.
@param {number} rows - Number of rows
@param {number} columns - Number of columns
@param {function} [rng=Math.random] - Random number generator
@return {Matrix} The new matrix