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matlabmatrixsymbolic-math

How to extract a matrix of symbolic functions in Matlab

syms c  A(t) v(t)
A(t) =
            0
 c*sin(tt(t))
 c*cos(tt(t))

How I can get X = A(2) = c*sin(tt(t)); (the function at second row)? If I type A(2), the result will be as below (it substitutes a constant for the function, which is not my desire):

>> A(2)
ans =
            0
 c*sin(tt(2))
 c*cos(tt(2))
Solution

  • The problem is that you've defined A as a symbolic function (symfun), not as an array of symbolic expressions. Instead:

    syms c A tt(t)
A = [0;
     c*sin(tt(t));
     c*sin(tt(t))];

    Now A(2) will return c*sin(tt(t)).

    Alternatively, if you can't change the definition of A(t), you'll need to assign it to an intermediate variable to convert it to an array of symbolic expressions:

    syms c  A(t) tt(t)
A(t) = [0;
        c*sin(tt(t));
        c*cos(tt(t))];
B = A(t);

    Then, B(2) will return c*sin(tt(t)). You can also use formula to extract the underlying expressions:

    B = formula(A):