MATLAB: Assign values to variables in a loop

arraydynamic variable namesfor loopMATLABsubssymbolicvariables

syms a [1 n];
...
for i=1:n-1
    ...
    a(i+1) = rhs(isolate(eqn,a(i+1)));
    a(i+1);
end
I'm trying to assign the expression rhs(isolate(eqn,a2)) to the symbolic variable a2, rhs(isolate(eqn,a3)) to a3, up to an.
I have absolutely no idea how to do this. a(i + 1) assigns the value to the array a, rather than the variable in a(i + 1). If I change i=1:n-1 to i=2:n and put ai, it only assumes ai to be some other variable, rather than replacing i with its value and referring to a2 or a3 or whatever.
What I'd like is for a(i + 1) to refer to the actual variable at that index location, rather than referring to the index location itself. Thing is, it actually does get a2 and a3 etc. in the isolate equation, but it doesn't on the left side???

Best Answer

We recommend against this. Dynamically assigning to full variables is trouble prone, and would tend to contribute to the confusion between variables at the MATLAB level and variables with the same name that exist in the symbolic engine.
You would be better off using subs(). One way would be to keep a cell array of symbolic variables (not a normal vector, a cell), and a another cell of corresponding values and then subs() in appropriate fragments using the subs(expression, cell, cell) calling syntax.
Another approach is to keep a scalar struct with one field per variable name with corresponding value set, and then use the subs(expression, struct) calling syntax. (Note: I recently found problems in the case where a struct member was empty even if that variable was not being substituted.)
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