Vectorizing for loops .. can't get the hang of it

[Joza]

I understand I should REALLY try use vectors instead of for loops ... anyone
care to explain how to do it? I come from a CS programming background so
traditional for loops always seem the easiest to me.

A piece of code I've used recently is below. I couldn't figure out how to
vectorize it. Where do i start?

for i=1:n
                sum = 0.0;
                
                if i==1
                        for j=1:2
                                sum = sum + A(i,j)*x(j);
                        end
                elseif i==n
                        for j=n-1:n
                                sum = sum + A(i,j)*x(j);
                        end
                else
                        for j=i-1:i+1
                                sum = sum + A(i,j)*x(j);
                        end
                end



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