MATLAB: How to define a vector that its elements are created in a For Loop

vector symbolic maths forloop

I would like to define a vector,X, with five elements:
syms a
X = zeros(1,5);
X(1) = 1;
for k = 1:4
  X(k+1)=X(k)+a^2;
end
Actually I need to have the vector X, that its elements should be based on variable a. But I face an error in MATLAB:
The following error occurred converting from sym to double:
Error using symengine (line 58)
DOUBLE cannot convert the input expression into a double array.
If the input expression contains a symbolic variable, use VPA.
Error in Code2 (line 5)
X(k+1)=X(k)*a^2;
when I write the code above. How to do this? Please Answer me if possible.

Best Answer

Define X as a sym vector from the start.
X = sym(zeros(1, 5));
Adding a double and a sym results in a sym, but attempting to assign a sym into an element of a double array requires MATLAB to convert the sym into a double. In this case MATLAB cannot perform that conversion, so you receive an error. If instead you attempt to assign a sym into an element of a sym array, no conversion is needed.
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