Matlab: creating an array of symfun

Question

I was trying to create a array of symfun, so that I may later access those functions and perform the diff operation w.r.t to the specific variables, I have searched and found the code as:

syms x
f = symfun([x1^2+x2-x3; x2+x3^2; x1*x2], x);

But is not the thing that I am looking for, this snippet is creating a symfun out of an array, but I need to create an array of symfun. So that if I have n symfun stored in an array and also have n variables stored in an array then want to create a matrix with the following rule:

[[diff(func_1, x1)    diff(func_1, x2) ...... diff(func_1, xn)]
 [diff(func_2, x1)    diff(func_2, x2) ...... diff(func_2, xn)]
  .
  .
  .
  .
 [diff(func_n, x1) .......................... diff(func_n, xn)]]

And here is my code:

function[K] = bigPopaPump()
x1 = sym('x1')
x2 = sym('x2')
f1 = symfun(3*x1+2, x1)
f2 = symfun(8*x2+5, x2)
funcs = [f1, f2]
xess = [x1, x2]
dummy_array = zeros(2, 2)
for i = 1:size(funcs)
    for j = 1:size(funcs)
        dummy_array(i, j) = diff(funcs(i), xess(j));
    end
end
display dummy_array
end

score 1 · Accepted Answer · edited May 23 '17 at 10:26

I assume you mean

syms x1 x2 x3
f = symfun([x1^2+x2-x3; x2+x3^2; x1*x2], [x1 x2 x3])

which returns

f(x1, x2, x3) =

 x1^2 + x2 - x3
      x3^2 + x2
          x1*x2

Similarly, this returns identical output:

syms x1 x2 x3
f = [symfun(x1^2+x2-x3, [x1 x2 x3]);
     symfun(x2+x3^2, [x1 x2 x3]);
     symfun(x1*x2, [x1 x2 x3])]

If you want an array of symfun's then you'll need to use cell array. The reason for this is that a symfun is effectively a function handle. One must use cell arrays rather than arrays to group function handles too.

For your example:

syms x1 x2 x3
f = {symfun(x1^2+x2-x3, [x1 x2 x3]);
     symfun(x2+x3^2, [x1 x2 x3]);
     symfun(x1*x2, [x1 x2 x3])}

or

syms x1 x2 x3
f = arrayfun(@(fx)symfun(fx,[x1 x2 x3]),[x1^2+x2-x3; x2+x3^2; x1*x2],'UniformOutput',false)

returns

f =

    [1x1 symfun]
    [1x1 symfun]
    [1x1 symfun]

You can then evaluate the first function, for example, via f{1}(2,3,4).

Matlab: creating an array of symfun

1 Answers1