Differentiating a symbolic function by a lot of variables without loop.

Hello. I am trying to create a script to calculate a function error (sqrt(sum(df/dvar * delta var)^2)) [Physics lab course] so I need to differentiate by a different variable each time. If I do this with a for loop, it works. If i try to do this:

exp = sum((diff(f, mat(:, 1))*mat(:, 2)).^2) % Symbolic Expression

it gives this error:

The second argument must be a variable or a nonnegative integer specifying the number of differentiations.

If fore example I change it for diff(f, mat(1, 1)) it gives no error (but differentiates by the same variable of course..)

So, any Ideas how could I do this w/o a loop? thank you! (The loop is:)

      for k=1:size(mat, 1);
          exp = exp+(diff(f, mat(k, 1))*mat(k, 2))^2;
      end

Answer 1

[John D'Errico]

Often people do things in MATLAB where they use loops excessively. So we seee code with heavily nested loops, when a simple matrix multiply would suffice.

Other times, I see people who seem terrified of loops, as if a simple loop is a bad thing. You are doing the same operations in any case, so a loop or not will not be more efficient here. And very often code that is written to avoid a loop at all costs is terribly difficult to read, difficult to debug.

In this case, the loop is simple. Easy to read and write. So why is there a need to avoid this loop? Just use the loop, and go on to the next part of your code.

[Samyon Shahnovitch]

Well, I think you may be right. Thank you very much!