Simple problem: Replacing a loop with a vector expression

Question

C Meek 2012-2-12

0
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编辑： Jan 2023-1-29

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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