MATLAB Help. Plugging in matrix of variables into existing function

Question

I have an existing function of two variables (x,y) called discriminant defined in the following way:

discriminant = xSecondPart * ySecondPart - xySecondPart.^2;

Where xSecondPart and ySecondPart are the second partial derivatives of a function f. xySecondPart is the partial derivative with respect to x of the partial derivative with respect to y of the same function f.

I need to print out the values of discriminant at each value of x in the matrix xAns.

The below code is not working...

for idx = 1:numel(xAns)
    disp(discriminant(xAns(idx)));
end

Hopefully someone can provide a solution. Thank you

Best...SL

Can you put the definition of the discriminant function? – PearsonArtPhoto Nov 18 '12 at 17:32 — PearsonArtPhoto, Nov 18 '12 at 17:32
ends up being this: 24*x^2 - 32 – Skyler Nov 18 '12 at 17:39 — Skyler, Nov 18 '12 at 17:39

score 2 · Accepted Answer · answered Nov 18 '12 at 18:02

If you define the function discriminant anonymously, like so:

    descriminant = @(x) 24*x.^2 - 32;

Then all you have to do is type the following statement in the command line or function you're running:

    D = discriminant(xAns)

If your function has been defined using the elementwise operator '.' wherever necessary, then the statement above will print out the discriminant function evaluated at every element of the matrix xAns, regardless of its size or shape. The values returned will be in the same shape as the matrix xAns. I think that would be the easiest way to solve your problem.

MATLAB Help. Plugging in matrix of variables into existing function

1 Answers1