syntax of fsolve

I am having some trouble with the fsolve syntax. In the code below value of m and x_length are known and constants. variables are B0 and A0 which are discretized. p is time and q is length. this code below is for a particular time . Please help

l = 1:m
q = 2:x_length; 

F(1: (x_length-1) ) =...
-[B0(p+1,q) - B0(p,q)] + const_a*[B0(p+1,q+1) - 2*B0(p+1,q) + B0(p+1,q-1) +     B0(p,q+1) - 2*B0(p,q) + B0(p,q-1)]- [[const_b*[B0(p+1,q)+B0(p,q)]].*[A0(p+1,q)+A0(p,q)]];  

F(((x_length-1)*(m+2)+1) :(x_length-1)*(m+3)  ) =...
-[A0(p+1,q)- A0(p,q)]    + const_a*[A0(p+1,q+1) - 2*A0(p+1,q) + A0(p+1,q-1) + A0(p,q+1) - 2*A0(p,q) + A0(p,q-1)] - [[0.5*const_b*[A0(p+1,q)+ A0(p,q)]].*[sigmab(p+1,q)];

F(((x_length-1) + 1):(x_length-1)*(m+2) ) =...
-[B0(p+1,(x_length+1)*l+q)- B0(p,(x_length+1)*l+q)] + (const_a/m)*[B0(p+1,(x_length+1)*l+q+1) - 2*B0(p+1,(x_length+1)*l+q) + B0(p+1,(x_length+1)*l+q-1) + B0(p,(x_length+1)*l+q+1) - 2*B0(p,(x_length+1)*l+q) + B0(p,(x_length+1)*l+q-1)] - [[(0.5*const_b)*[A0(p+1,q)+ A0(p,q)]].*[B0(p+1,q)+ B0(p,q)]] + [[(const_b*2)*(A0(p+1,q) + A0(p,q))].*[sigmac(p+1,(x_length+1)*(l-1)+q)]]./[sigmab(p+1,q)] ;

Answer 1

[Sargondjani]

you should write it as a function (in either anonymous function, function file or subfunction if your main program is also a function). Let's say you make a function file:

function [F]=my_fun(var1,var2,par1,par2,....)
F(1:x_length,1)=.....
F(x_length+1:....)=
end

Then if you want to solve for var1 and var2: f_obj=@(x)my_fun(x(1),x(2),par1,par2,...); %anonymous function fsolve(f_obj,x0)

with x0 containing two values (var1_0 and var2_0)