matrix_multiplication.ts

/**
 * @function matrixMultiplication
 * @description Multiply a matrix with either another matrix, a vector or a scalar
 * @param {Number[][]} matA - An array of an array of numbers
 * @param {Number[][] | Number[] | Number} b - Either an array of an array of numbers, an array of numbers, or a number
 * @return {Number[][] | Number[]} - Either an array of an array of numbers, or an array of numbers
 * @example matrixMultiplication([[1, 2], [3, 4]], [[1, 2], [3, 4]]) = [[7, 10], [15, 22]]
 * @example GreatestCommonFactor([[1, 2], [3, 4]], 2) = [[2, 4], [6, 8]]
 * @example GreatestCommonFactor([[1, 2], [3, 4]], [1, 2]) = [5, 11]
 */

function matrixMultiplication(matA: number[][], b: number[][]): number[][];
function matrixMultiplication(matA: number[][], b: number): number[][];
function matrixMultiplication(matA: number[][], b: number[]): number[];

function matrixMultiplication(matA: number[][], b: any): Number[][] | Number[] | null {
  let matC: any = null;

  if (typeof b === 'number') {
    matC = matA.map(row => row.map(colVal => colVal * b));
  } else {
    if (matA[0].length !== b.length) {
      return null;
    }

    if (typeof b[0] === 'number') {
      matC = matA.map(row => row.reduce((sum, colVal, i) => sum + colVal * b[i], 0));
    } else {
      matC = new Array(matA.length).fill(null).map(() => new Array(b[0].length).fill(0));
      let i: number, j: number, k: number;

      for (i = 0; i < matA.length; i++) {
        for (j = 0; j < b[0].length; j++) {
          for (k = 0; k < matA[0].length; k++) {
            matC[i][j] += matA[i][k] * b[k][j];
          }
        }
      }
    }
  }
  return matC;
}

export { matrixMultiplication };