Partial derivatives of the inline function

I have defined an inline function in a script

function a = Test(A,B,C)

I want to symbolically define partial derivatives of this Test function with respect to A, B, C. Please advise.

Answer 1

[Star Strider]

Your Question lacks detail. The jacobian (link) function is likely what you want. Another option is the gradient (link) function, depending on the result you want.

Answer 2

[Walter Roberson]

syms A B C
fun = Test(A,B,C);

Now fun will be a symbolic expression involving A, B, C, that you can calculate gradient of, or can directly calculate

diff(fun, A)

for example.

Note that this will not work if Test uses "if" statements testing the values of the inputs, or does logical indexing based upon the values, or if it initializes vectors or arrays to zeros() and tries to assign values calculated from A, B, C into them. Sometimes you need to change a function a bit to make it usable with symbolic inputs. Sometimes you need to resort to tests such as

if issym(A) || issym(B) || issym(C)
   y = piecewise(....);
else
  if A < pi || B > sqrt(2)
    y = 11;
  else
   y = 9;
  end
end

-- that is, sometimes you need to test if you are doing symbolic work and create a piecewise() expression because you cannot test unresolved symbols against specific numbers.