Assign values to n symbolic variables

I have symbolic variables that goes from 1 to a user assigned value 'n' (i.e. x1,x2,x3,...,xn). Is there any way I can assign a value to each of these symbolic variables? I have a matrix 's' of size (1,n) with the input values. Ideally, I want it to work something like this:

   for i = 1:n
      x(i) = s(i)
   end

Answer 1

[Sameer]

Hi @David Pham

You can assign values to a set of symbolic variables like "x1", "x2", ..., "xn" using symbolic toolbox. The best way is to create a symbolic vector and then substitute the values using the "subs" function.

Here’s how you can do it step-by-step:

syms x [1 n]  % creates symbolic variables x1, x2, ..., xn as a vector

% Suppose s is your 1-by-n matrix of values
s = [value1, value2, ..., valuen];  % replace with your actual values
    
% Now substitute each xi with the corresponding value in s
expr = x;  % or any symbolic expression involving x
expr_substituted = subs(expr, x, s);

% expr_substituted now has each xi replaced by s(i)

If you want to assign values individually (though not usually necessary), you could do:

for i = 1:n
    assignin('base', sprintf('x%d', i), s(i))
end

But the preferred symbolic approach is using "subs".

https://www.mathworks.com/help/symbolic/sym.subs.html

Example:

n = 3;
syms x [1 n]
s = [10, 20, 30];

expr = x(1)^2 + x(2)*x(3);
expr_substituted = subs(expr, x, s);
disp(expr_substituted)  % Output: 10^2 + 20*30 = 100 + 600 = 700

Hope this helps!