Calling Octave interpolation function within function body - function

Question

I'm trying to wrap Octave interpolation function in a function body,
function FUN = inter(p);
FUN = interpn (x1, x2, x3, x4, x5, A, p(1), p(2), p(3), p(4), p(5), "spline");
end
The reason why I'm doing this is because I'm using a package which function needs a string name function which would be in this case packageFunction("inter", argument1);
The issue is calling now for instance like,
disp("value = "), inter([10 2 4 3 4])
doesn't work; Doesn't see the vectors error: 'x1' undefined ,
Of course the vectors xi and matrix A are defined above the function body. Would appreciate advice on this,
thanks, Damir
------------- in file example1.m
[a b c] = fminuit('gaussian','mnplot',[10 166 33],[x;y;dy])
------------- in file gaussian.m
function f = gaussian(par,data);
%theoretical function
f = par(1)/(sqrt(2*pi)*par(3)) * exp(-.5*((data(1,:)-
par(2))./par(3)).^2);
if (size(data,1)==2), %chi-square, error = 1
f = sum((data(2,:) - f).^2);
elseif (size(data,1)>2), %chi-square, error = 3rd row of data
f = sum(((data(2,:) - f)./data(3,:)).^2);
end

Answer 1

Given you are using an old function that requires a string as the function, the first solution below will not work. This is, however, the right way to do it. Changing the old function to use function handles instead of strings would be my preferred solution. However, you can also use an alternative solution further down below, which uses global variables. This is not the recommended approach (we should strive to avoid globals), but will solve your near-term problems.
Correct approach: use an anonymous function
You should use an anonymous function, these can capture variables when they're defined:
inter = #(p)interpn (x1, x2, x3, x4, x5, A, p(1), p(2), p(3), p(4), p(5), "spline");
Now inter(p) works just as if inter had been declared as a normal function. But the values of x1, x2, etc as they were defined when inter was defined will be stored inside inter.
As stated, the function you pass inter to must be written to accept function handles.
Bad, quick solution: use global variables
First, create a file inter.m with the following contents:
function FUN = inter(p);
global x1 x2 x3 x4 x5 A
FUN = interpn (x1, x2, x3, x4, x5, A, p(1), p(2), p(3), p(4), p(5), "spline");
end
Next, in your function of script that calls inter, again declare the global variables (currently MATLAB warns that you should declare them as globals before giving them a value, in future versions this will be required):
global x1 x2 x3 x4 x5 A
x1 = ...
x2 = ...
% etc
inter([10 2 4 3 4])
% or:
fminuit('inter',...)