debugging limit Error using sym/subsindex

syms k
    f = 2*l1^k*v1 + 1*l2^k*v2 + 3*l3^k*v3
    limit(f,k,inf)

This is giving me an error :

Error using sym/subsindex (line 857)

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression.

Error in sym/subsref (line 902)

R_tilde = builtin('subsref',L_tilde,Idx);

Error in Exploration10 (line 40)

limit(f(x),x,inf)

I tried

syms x h
    f = 2*x;
    limit(f,x,inf)

But it gives me the same error. What am I doing wrong

Answer 1

[Steven Lord]

The code you posted is not the code you ran. What you said you ran was:

syms k
    f = 2*l1^k*v1 + 1*l2^k*v2 + 3*l3^k*v3
    limit(f,k,inf)

What the error message says you ran was:

    limit(f(x),x,inf)

Don't try to index into a variable (other than a symbolic function, which is less indexing and more evaluation) with a symbolic variable.

syms q
x = 1:10;
x(q) % will fail with the same error

syms g(x) x t
g(x) = sin(x); % symbolic function
g(t) % sin(t)