Iterating in function handles

I am trying to solve an SDE (using SDETools). Here is a simplified version of the SDE.

I need to input function handles, f and g, for the 'dt' and 'dw' components respectively. For example,

g = @(t, x) sig;

would define the function handle for g given a pre-defined array sig. Now, I would like to define the function handle , where are coefficients that depend on i and j. For the purpose of this example, assume that. How can I define a single function handle that returns a column vector that does what I want?

If it helps, when , I was able to do

f = @(t, x) mean(x) - x; 

But I'm stuck on how to adapt this to include the . I think I need to iterate over i and j inside the function, but don't know if this is correct. Thanks in advance.

[Torsten]

Don't use function handles for compliciated expressions. Write functions instead.

[Harry Li]

The problem is that I need to input f as a function handle for the SDE solver.

[Torsten]

Yes, but the function handle can point to a function.

f = @(t,x)fun(t,x)
%Call SDE with function handle f

function res = fun(t,x)
  % Calculate whatever you like
  res = something;
end 

[Harry Li]

That makes sense, thank you.