TheAlgorithms · ruppysuppy · Oct 13, 2020 · Oct 12, 2020 · Oct 12, 2020 · Oct 12, 2020
@@ -0,0 +1,91 @@
+// Wikipedia URL for General Matrix Multiplication Concepts: https://en.wikipedia.org/wiki/Matrix_multiplication
+
+// This algorithm has multiple functions that ultimately check if the inputs are actually matrices and if two Matrices (that can be different sizes) can be multiplied together.
+// matrices that are of the same size [2x2]x[2x2], and the second is the multiplication of two matrices that are not the same size [2x3]x[3x2].
+
+// MatrixCheck tests to see if all of the rows of the matrix inputted have similar size columns
+const matrixCheck = (matrix) => {
+  let columnNumb
+  for (let index = 0; index < matrix.length; index++) {
+    if (index === 0) {
+      columnNumb = matrix[index].length
+    } else if (matrix[index].length !== columnNumb) {
+      console.log('The columns in this array are not equal')
+    } else {
+      return columnNumb
+    }
+  }
+}
+
+// tests to see if the matrices have a like side, i.e. the row length on the first matrix matches the column length on the second matrix, or vise versa.
+const twoMatricesCheck = (first, second) => {
+  const [firstRowLength, secondRowLength, firstColLength, secondColLength] = [first.length, second.length, matrixCheck(first), matrixCheck(second)]
+  if (firstRowLength !== secondColLength || secondRowLength !== firstColLength) {
+    console.log('These matrices do not have a common side')
+    return false
+  } else {
+    return true
+  }
+}
+
+// returns an empty array that has the same number of rows as the left matrix being multiplied.
+// Uses Array.prototype.map() to loop over the first (or left) matrix and returns an empty array on each iteration.
+const initiateEmptyArray = (first, second) => {
+  if (twoMatricesCheck(first, second)) {
+    const emptyArray = first.map(() => {
+      return ['']
+    })
+    return emptyArray
+  } else {
+    return false
+  }
+}
+
+// Finally, `matrixMult` uses `Array.prototype.push()`, multiple layers of nested `for` loops, the addition assignment `+=` operator and multiplication operator `*` to perform the dot product between two matrices of differing sizes.
+// Dot product, takes the row of the first matrix and multiplies it by the column of the second matrix, the `twoMatricesCheck` tested to see if they were the same size already.
+// The dot product for each iteration is then saved to its respective index into `multMatrix`.
+const matrixMult = (firstArray, secondArray) => {
+  const multMatrix = initiateEmptyArray(firstArray, secondArray)
+  for (let rm = 0; rm < firstArray.length; rm++) {
+    const rowMult = []
+    for (let col = 0; col < firstArray[0].length; col++) {
+      rowMult.push(firstArray[rm][col])
+    }
+    for (let cm = 0; cm < firstArray.length; cm++) {
+      const colMult = []
+      for (let row = 0; row < secondArray.length; row++) {
+        colMult.push(secondArray[row][cm])
+      }
+      let newNumb = 0
+      for (let index = 0; index < rowMult.length; index++) {
+        newNumb += rowMult[index] * colMult[index]
+      }
+      multMatrix[rm][cm] = newNumb
+    }
+  }
+  return multMatrix
+}
+
+const firstMatrix = [
+  [1, 2],
+  [3, 4]
+]
+
+const secondMatrix = [
+  [5, 6],
+  [7, 8]
+]
+
+console.log(matrixMult(firstMatrix, secondMatrix)) // [ [ 19, 22 ], [ 43, 50 ] ]
+
+const thirdMatrix = [
+  [-1, 4, 1],
+  [7, -6, 2]
+]
+const fourthMatrix = [
+  [2, -2],
+  [5, 3],
+  [3, 2]
+]
+
+console.log(matrixMult(thirdMatrix, fourthMatrix)) // [ [ 21, 16 ], [ -10, -28 ] ]
@@ -13,6 +13,7 @@
     "@babel/plugin-transform-runtime": "^7.11.5",
     "@babel/preset-env": "^7.11.5",
     "jsdom": "^16.3.0",
+    "node": "^14.13.1",
     "node-fetch": "2.6.1"
   },
   "standard": {