Vector using in a function in matlab

Question

I have a problem about matlab code. I have a specific one variable function, and i want to assign a vector or array in this function as ax value. But i didn't reach success. A part of my code is at below:

a=-5; b=10; n=20;  %[a,b] interval range and n is number of interval
sz = (b-a)/n; %interval size
t=1; %iteration number
for i=1:n
I(i,:,t) = [a+(i-1)*sz a+i*sz]; %interval
x(i,:,t) = a+(i-0.5)*sz; %midpoint of interval
end
f= x.^2-3.*x+5; %my sample function
for i=1:n
        if i==1  
            j=i+1;
            neigbor(i,:,t) = I(j,:,t);  %neigbor of interval I1's
            h_f(i,:,t) =abs(f(x(i,:,t))-f(x(j,:,t)));  %heuristic value

            prob(i,:,t)=(ph(j,:,t).*h_f(i,:,t))./(ph(j,:,t).*h_f(i,:,t)); %probability
...

Other if conditions are following this code, but i check this below portion with sample i and j value, it gives error like this : "Subscript indices must either be real positive integers or logicals."

 h_f(i,:,t) =abs(f(x(i,:,t))-f(x(j,:,t)));

What don't i know? What is my mistake? Can you suggest anything? If you need complete code, i can post.

Edit : Actually this function f returns value by using itself. But it doesn't return value in comment h_f(i,:,t)= abs((f(x(i,:,t)-x(j,:,t))

Solution Edit: After creating separate function m file, and calling in main function. Don't need to write x array in f.

Answer 1

In Matlab, you need to declare functions in a separate .m file. I created a separate file "fm" and inserted the following code:

function return_val = f(x)

return_val = x.^2-3.*x+5; %my sample function

end

Then, in your main file, you can call this function as follows:

a=-5; b=10; n=20;  %[a,b] interval range and n is number of interval
sz = (b-a)/n; %interval size
t=1; %iteration number
for i=1:n
    I(i,:,t) = [a+(i-1)*sz a+i*sz]; %interval
    x(i,:,t) = a+(i-0.5)*sz; %midpoint of interval
end

f = f(x)

Hope this helps.

Answer 2

As was posted you can create f as a function in a file but you can also inline the function with a handle. This is done as follows:

f = @(x) x.^2 - 3.*x + 5;

The f is the function handle with x as an input, see more information here: http://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html .

This new f is then used as you would expect.

>> f(2)

ans =

     3

>> f(5)

ans =

    15

>> f(1:3)

ans =

     3     3     5

>> f(4:10)

ans =

     9    15    23    33    45    59    75