Simple problem: Replacing a loop with a vector expression

Hi all,

I'd like to run this by people here as I can't see where I'm going wrong, despite this seeming pretty simple.

I have the following loop:

for n=M+1:N

y(n)=a*x(n)+x(n-M)-a*y(n-M); 

end

I wish to implement this as a vector expression. Here is what I have got:

y(M+1:N)=a*x(M+1:N)+x(1:N-M)-a*y(1:N-M);

I'd thought this was correct, but when I do simple (or complicated) examples, the values are only the same up to a certain point. I've noticed that they are correct up to the entry that is double of the value of M (so if M=8, the outputs produced by both examples are the same up until the 16th entry in the vector).

Can anyone have a look at this and correct me if I've made a mistake? As usual it may be something simple, but I'm not seeing it!

Craig

Answer 1

[Jan]

See http://www.mathworks.com/matlabcentral/answers/28396-speed-up-recursive-loop

[Jan]

Austin Chen wrote a flag at 28 Jan 2023 at 3:22: "terrible response"

@Austin: You find an exhaustive discussion and some example code in this link.

If you know a better answer, feel free to post it.