MATLAB: Evaluating a function defined by “sym” command

Question

Hello

I am using "sym" command to define the variables in small expressions that form the elements of a matrix. Eventually i have to diagonalize the matrix to find eigenvalues. With sym command lets say i define –

f = a*x^2+b*x;

Now i want to evaluate the magnitude of 'f' by putting in numerical values for a,b and x. a and b are constants but x would be an array. How can define the values of a,b and x to find numerical answer for f under these circumstance?

Thanks

Answer 1

Use subs:

syms a b x
f = a*x^2+b*x;
subs(f,{a,b,x},{1,2,magic(3)})

And for more info:

doc subs