How to define function or variable 'x'?

I want to write an algorithm for minimizing a function bounded by some constraints (non linear and linear functions) without using the optimization toolbox but some optimization method. I have given the objective function in a 'minimize.m' file and constraint in another 'nonlin.m' and 'lin.m' file. Now as I call the function in my algorithm 'ALU.m' file and try to run, it shows "Undefined function or variable 'x' ". I had given below my algorithm starting part. Please help me where I am doing wrong. I would be very thankful.

fun = @minimize;
G = @nonlin;
H = @lin;
var = input('number of variables= ');
s = input('number of non-linear constraints= ');
u = input('number of linear constraints= ');
i = 1; j = 1; k = 1;
x = sym(x);

Answer 1

[Stephen23]

sym('x')