MATLAB: Symbolic variables product does not produce symbolic result (Symbolic for loop)

Question

Hello, I have a problem with making symbolic variables. I want to have symbolic variables by user input. For example, when there are 3 variables, I will have S1, S2, S3.

This is what i've done so far:

num_sp = 'Number of variables: ';
K = input(num_sp);
% I've tried this
for i=1:K
eval(sprintf('S%d = sym(''S%d'')', i,i))
end 
% OR THIS (but not both)
for i=1:K
syms (['S', num2str(i)])
end 
syms E
obj_fun = cost_eng *E
for i=1:K
% 1st Case
obj_fun = obj_fun + (cost_inv(i) * (sprintf('S%d', i))
% or 2nd Case
obj_fun = obj_fun + (cost_inv(i) * (['S', num2str(i)]) )
end

However both gives me the answer of:

[ 2*E + 332, 2*E + 198]

for K = 2.

I don't know how the length becomes 2, when what I want is something like this:

obj_fun = cost_eng * E + cost1 * S1 + cost2 * S2

I've tried checking each elements but both is are not 2×1 matrix.

Answer 1

Try:

Ssym = sym('S', [1 5])

Now work with the elements of Ssym.