在 Javascript 中乘以 2 个矩阵 [英] Multiply 2 matrices in Javascript

问题描述

我正在做一个乘以 2 个矩阵的函数.矩阵将始终具有相同的行数和列数.(2x2, 5x5, 23x23, ...)

I'm doing a function that multiplies 2 matrices. The matrices will always have the same number of rows and columns. (2x2, 5x5, 23x23, ...)

当我打印它时，它不起作用.为什么?

When I print it, it doesn't work. Why?

例如，如果我创建两个 2x2 矩阵:

For example, if I create two 2x2 matrices:

矩阵A:

[1][2]

[3][4]

矩阵B:

[5][6]

[7][8]

结果应该是:

[19][22]

[43][50]

(http://ncalculators.com/matrix/2x2-matrix-multiplication-calculator.htm)

但是，我明白了:

[19][undefined]

[22][indefined]

function multiplyMatrix(matrixA, matrixB)
{
    var result = new Array();//declare an array   

    //var numColsRows=$("#matrixRC").val();
    numColsRows=2;
    
    //iterating through first matrix rows
    for (var i = 0; i < numColsRows; i++) 
    {
        //iterating through second matrix columns
        for (var j = 0; j < numColsRows; j++) 
        { 
            var matrixRow = new Array();//declare an array
            var rrr = new Array();
            var resu = new Array();
            //calculating sum of pairwise products
            for (var k = 0; k < numColsRows; k++) 
            {
                rrr.push(parseInt(matrixA[i][k])*parseInt(matrixB[k][j]));
            }//for 3
            resu.push(parseInt(rrr[i])+parseInt(rrr[i+1]));

            result.push(resu);
            //result.push(matrixRow);
        }//for 2
    }//for 1
    return result;
}// function multiplyMatrix

推荐答案

您对各种临时数组感到困惑.undefined 值是由最内层循环下方行的越界访问引起的.

You're getting confused with your various temporary arrays. The undefined values are caused by out-of-bounds access on the line below your innermost loop.

我建议您坚持为乘法结果创建一个数组.您可能知道，问题在于 JavaScript 不允许您初始化多维数组.要创建一个二维数组，您必须初始化一个一维数组，然后迭代它的元素并将每个元素初始化为一个一维数组.

I recommend that you stick to making a single array for the result of the multiplication. As you're probably aware, the hitch is that JavaScript doesn't allow you to initialize a multi-dimensional array. To make a two-dimensional array, you have to initialize a one-dimensional array, then iterate over its elements and initialize each one to a one-dimensional array.

function multiply(a, b) {
  var aNumRows = a.length, aNumCols = a[0].length,
      bNumRows = b.length, bNumCols = b[0].length,
      m = new Array(aNumRows);  // initialize array of rows
  for (var r = 0; r < aNumRows; ++r) {
    m[r] = new Array(bNumCols); // initialize the current row
    for (var c = 0; c < bNumCols; ++c) {
      m[r][c] = 0;             // initialize the current cell
      for (var i = 0; i < aNumCols; ++i) {
        m[r][c] += a[r][i] * b[i][c];
      }
    }
  }
  return m;
}

function display(m) {
  for (var r = 0; r < m.length; ++r) {
    document.write('&nbsp;&nbsp;'+m[r].join(' ')+'<br />');
  }
}

var a = [[8, 3], [2, 4], [3, 6]],
    b = [[1, 2, 3], [4, 6, 8]];
document.write('matrix a:<br />');
display(a);
document.write('matrix b:<br />');
display(b);
document.write('a * b =<br />');
display(multiply(a, b));

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