Formula Logic Help

[sehudson]

Hello,

I was given the following formula to calculate a determinant:

  public double calculateDeterminant() {


        double det = 0;
        System.out.println("RowCount: " + RowCount);
        if (RowCount == 1) {
            det = CalculateBaseCase("1");
            return det;
        }
        //base case
        if (RowCount == 2) {
            det = CalculateBaseCase("2");
            return det;
        }

        for (int i = 0; i < RowCount; i++) {
            det = Math.pow(-1, i) * getValAt(i, 0) * minor(i,0).calculateDeterminant();
        }
        return det;

    }

I have some println statements in place, and it seems like my i for the 'minor(i,0)' method stays at 0. Anybody able to tell me where the formula is wrong?

[Junky]

Think about what your loop is doing.

int val;
for(int i = 1; i <= 10; i++) {
    val = i;
}
System.out.println(val);

The output is 10. The above code can be simplified to

int val = 10;
System.out.println(val);

Do you understand what I'm getting at?

[sehudson]

partially..since in your example the println is outside the loop, the only thing that gets printed is the last loop value, which is 10.

[sehudson]

not exactly sure.

[Junky]

The print statement is irrelevant. It was included in case the code was compiled and run to see the output.

The point I was trying to make is that your loop is pointless only the last value is retained. When i is 1, perform calculation, assign to det. Then i is 2, perform calculation, assign to det, throw away first result. Then i is 3, perform calculation, assign to det, throw away second result, etc. Your loop can be replaced with:

det = Math.pow(-1, RowCount - 1) * getValAt(RowCount - 1, 0) * minor(RowCount - 1,0).calculateDeterminant();