Question

What is a good way to implement Gaussian elimination when the operators are custom operators, rather then standard arithmetic ones?

Here are the operators:

Addition:

0 + 0 = 0
0 + 1 = 1
1 + 1 = 0

Subtraction:

0 - 0 = 0
0 - 1 = 1
1 - 1 = 0

Multiplication:

0 * 0 = 0
0 * 1 = 0
1 * 1 = 1

Division:

0 / 0 = illegal
0 / 1 = 0
1 / 1 = 1

Here is a sample set of equations as augmented matrix, with the RHS in the right-most column:

1, 1, 0, 1, 0, 0, 0, 0, 0, 1
0, 1, 0, 1, 1, 0, 0, 0, 0, 1
0, 1, 1, 0, 0, 1, 0, 0, 0, 1
1, 0, 0, 1, 0, 0, 0, 0, 0, 1
0, 1, 0, 1, 1, 0, 0, 0, 0, 1
0, 0, 0, 0, 0, 1, 0, 0, 0, 1
0, 0, 0, 1, 0, 0, 1, 0, 0, 1
0, 0, 0, 1, 1, 0, 1, 1, 0, 1
0, 0, 0, 0, 0, 1, 0, 0, 1, 1

The solution for this set is:

x1 = 1
x2 = 0
x3 = 0
x4 = 0
x5 = 1
x6 = 1
x7 = 1
x8 = 1
x9 = 0

Gaussian elimination failed for me as I tried it on this set.

The equations will have 9, 16, 25 or 36 terms. It would be great if the algorithm is easily extendable to larger squares, up to 100.
I’m looking for an algorithm, in pseudo code or JavaScript preferably.

Answer 1

Gaussian Elimination Algorithm in pseudocode can be found here.

It doesn’t matter if you are using ‘normal’ numbers or if you are in Z₂ ring, the algorithm remains the same.

What you could do is implement a structure to hold the values you are operating over and overload all necessary operators. Then all you need to do will be to rewrite pseudocode to the language you want to use it in.

Unfortunately since you have mentioned JavaScript you cannot override operators in that language so this will become a bit more complex. I guess you could define functions that will perform operators job and use them instead of standard operators.

function add(v1, v2) {
    if ((v1 != 0 && v1 != 1) || (v2 != 0 && v2 != 1)) {
        alert('Invalid params');
        return;
    }

    return (v1 + v2) % 2;
}

function subtract(v1, v2) {
    if ((v1 != 0 && v1 != 1) || (v2 != 0 && v2 != 1)) {
        alert('Invalid params');
        return;
    }

    return Math.abs((v1 - v2) % 2);
}

function multiply(v1, v2) {
    if ((v1 != 0 && v1 != 1) || (v2 != 0 && v2 != 1)) {
        alert('Invalid params');
        return;
    }

    return v1 * v2;
}

function divide(v1, v2) {
    if ((v1 != 0 && v1 != 1) || (v2 != 0 && v2 != 1)) {
        alert('Invalid params');
        return;
    } else if (v2 == 0) {
        alert('Divider cannot be zero');
        return;
    }

    return v1 / v2;
}