Matlab - using symbolic variables for a for loop with numeric inputs

I am new to Matlab therefore please excuse the simplicity of my question:

I am calculating option prices and throughout my calculations I have defined certain variables as symbolic variables in order to integrate the functions in terms of these variables.

However, once I have all my equations I need to create a for-loop with a range of numeric values for these said symbolic variables. However, I receive following error message:

"Error using sym/subsindex (line 769) Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic variables and the body of the function is a SYM expression. When indexing, the input must be numeric, logical, or ':'. Error in sym/subsref (line 814) R_tilde = builtin('subsref',L_tilde,Idx);"

How can I fix this?

Thank you very much

Chloe