Javascript function returning array but only the last array

Question

I try to make a JavaScript function to show steps of solving a Linear Equation System using the Gauss method. What I got so far (only small part of Gauss elimination method, constructing leading zeros):

let mt = [[2, 3, -1, 5], [4, 0, -3, 3], [-2, 3, -1, 1]];
gaussMethod(mt);

function gaussMethod(mtx) {
    window.GaussMatrixSteps = [];
    window.GaussMatrixSteps[0] = mtx;
    let n = mtx.length;

    for (i = 0; i < n; i++) {
        for (k = i + 1; k < n; k++) {
            var multiplier = mtx[k][i] / mtx[i][i];
            for (j = 0; j <= n; j++) {
                mtx[k][j] = mtx[k][j] - mtx[i][j] * multiplier;
            }
        }
        window.GaussMatrixSteps[i + 1] = mtx;
    }
}

What I get, window.GaussMatrixSteps is an array of same matrices (the last step) instead of different matrices from the different steps. Is it really how JavaScript works?

Answer 1

Your issue is that you're setting an array to the first element of another array.

let mt = [[2, 3, -1, 5], [4, 0, -3, 3], [-2, 3, -1, 1]];
gaussMethod(mt);

function gaussMethod(mtx) {
    window.GaussMatrixSteps = [];
    window.GaussMatrixSteps[0] = mtx;  // issue is here
    let n = mtx.length;

You're creating this

    [0] = [[2, 3, -1, 5], [4, 0, -3, 3], [-2, 3, -1, 1]]
    [1] = null

What you need to do is remove the reference to the first array or just reuse that array.

---

You also need to get into the habit of declaring all of your variables using let or const and avoid using the window object as a variable placeholder. So, you can use a private variable inside your function and return it like this:

const GaussMatrixSteps = gaussMethod(mt);

function gaussMethod(mtx) {
    const GaussMatrixSteps = [];
    GaussMatrixSteps[0] = mtx;
    ... CODE HERE
    return GaussMatrixSteps;
}

Also, don't forget to declare the inner for loop variables like this:

    for (let i = 0; i < n; i++) {
        for (let k = i + 1; k < n; k++) {
            for (let j = 0; j <= n; j++) {
            }
        }
    }