MATLAB: How to convert a matrix/vector of symbolic variable into an anonymous function (matlabFunction)

Question

Suppose I have the following:

syms  x y
Vec_sym = [1/x, x/(x^2 + y^2), y/x];               %1x3 symbolic vector
Matrix_sym = [1/x,      x/(x^2 + y^2),        y/x;
              2/x,    x/(2*x^2 + y^2),    y/(6*x);
              9/x,  4*x/(x^2 + 2*y^2),      2*y/x];%3x3 symbolic matrix
Vec_func = matlabFunction(Vec_sym );               %Converting to matlabFunction

Matrix_func = matlabFunction(Matrix_sym );         %Converting to matlabFunction

The output of 'Vec_func' or 'Matrix_func' is always a 1×1 matlabFunction, which I do not want. How can I modify this code such that by entering the following, I get:

Vec_func(1,1) = [1, 0.5, 1];
Matrix_func(1,1) = [1,  0.5,    1;
                    2, 0.333, 0.167;
                    9, 1.333,    2] %please ignore the precision after decimal

I want to put this function in ode solver, ans using 'subs' and other symbolic operators take a lot of time, which is agonizing. Note that the variables x, y change/update within the ode code and the above is just a simplified example, in the real scenario I have a, say 10×1 vector and 5×5 matrix. Thanks a lot in advance, as the documentation of 'matlabFunctions' did not help me much.

Answer 1

You're confusing two different sizes. The output of matlabFunction is a function handle. Non-scalar function handle arrays are not allowed. But the fact that Vec_func and Matrix_func are scalar function handles is irrelevant in this case. You're not interested in the size of the function handle, you're interested in the size of the array the function handle returns when it is called. That can be non-scalar, and for your particular function handles those arrays are non-scalar.

syms  x y
Vec_sym = [1/x, x/(x^2 + y^2), y/x];               %1x3 symbolic vector
Matrix_sym = [1/x,      x/(x^2 + y^2),        y/x;
              2/x,    x/(2*x^2 + y^2),    y/(6*x);
              9/x,  4*x/(x^2 + 2*y^2),      2*y/x];%3x3 symbolic matrix
Vec_func = matlabFunction(Vec_sym );               %Converting to matlabFunction

Matrix_func = matlabFunction(Matrix_sym );         %Converting to matlabFunction
szVec = size(Vec_func)
szMat = size(Matrix_func)

That code displays (in format compact, which just gets rid of a few blank lines):

szVec =
   1     1
szMat =
   1     1

What happens when you evaluate Vec_func and Matrix_func?

>> Vec_func(1, 1)
ans =
    1.0000    0.5000    1.0000
>> Matrix_func(1, 1)
ans =
    1.0000    0.5000    1.0000
    2.0000    0.3333    0.1667
    9.0000    1.3333    2.0000