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

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.

[Adam]

If you get an error then post it! It's no help to use if you just say you get 'an error' and leave us to try to work out what the error is just by looking at the code.

[Stephen23]

@Ali Remo: please edit your question and provide us with the complete error message. This means all of the red text.

[John Chilleri]

You're trying to add a number and a symbol. What is a? are you trying to have the elements of X be strings like x(2) = 'a^2 + 1'?

Answer 1

[Steven Lord]

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.