make this matlab snippet run without a loop

Question

I want a code the below code more efficient timewise. preferably without a loop.

arguments:

t % time values vector
t_index = c % one of the possible indices ranging from 1:length(t).
A % a MXN array where M = length(t)
B % a 1XN array

code:

m = 1;
for k = t_index:length(t)
        A(k,1:(end-m+1)) = A(k,1:(end-m+1)) + B(m:end); 
        m = m + 1;
end

Many thanks.

bla · Accepted Answer · 2013-04-27 00:43:13Z

2

I'd built from B a matrix of size NxM (call it B2), with zeros in the right places and a triangular from according to the conditions and then all you need to do is A+B2.

something like this:

N=size(A,2);
B2=zeros(size(A));
k=c:length(t);
B2(k(1):k(N),:)=hankel(B)
ans=A+B2;

Note, the fact that it is "vectorized" doesn't mean it is faster these days. Matlab's JIT makes for loops comparable and sometimes faster than built-in vectorized options.

edited Apr 27, 2013 at 0:43

answered Apr 26, 2013 at 22:41

bla

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3 Comments

Amro Over a year ago

I had a similar solution but I deleted it, I couldn't get it quite right :) Not to mention that I got out-of-memory errors from the hankel function with the sizes the OP was using

bla Over a year ago

I'm not sure this is better than the for loop in performance at all. Why would the hankel get you out of memory?

user2324712 Over a year ago

actually a for loop does a better job on my computer... Many thanks anyways, i've still learned quite alot from the experience.

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