optimizing a matlab code involving for loop

Question

I have a Matlab code that goes like this

s=[0.5 0.6 0.7];
u=[0.3618   0.9826  0.7237  0.0346  0.5525  0.0692  0.8949  0.1384 
   0.3418   0.9226  0.7213  0.0346  0.7525  0.0692  0.8949  0.1384
   0.3318   0.9326  0.7237  0.0336  0.5575  0.0792  0.8949  0.1385]
A= u(1:2:7);  % Here u is a 1-D vector and hence A
B=u(2:2:8);   % Here u is a 1-D vector and hence B

C=mod(s(1)-(A+B),1);

I want to implement this code for the other two values of s also using next 8 values of u i.e now my code becomes

 A=u(9:2:15);
 B=u(10:2:16);
 C=mod(s(2)-(A+B),1);

Similarly for last value of s. But each time i need the next 8 values of u. How do i code this so that it takes less time.

Durkee · Accepted Answer · 2019-01-05 19:12:20Z

2

So you start with a 24 element array in u that you wish to perform this operation on in a vectorized fashion. I assume you have many more elements but that they all fit in memory. The way to do this is to reshape u to where you want the elements to be. You can do this via:

u1 = reshape(u1,[2,4,3]);

From there you also need to modify s to match it

s1 = permute(s,[1 3 2]);

Finally, you can calculate your C matrix in vectorized form

C1 = mod(s1-sum(u1),1);

For this problem, this gives a 1x4x3 matrix where the 3rd dimension represents each set of 8. From there you can then extract the problem set you want

C = squeeze(C1(1,:,1));

answered Jan 5, 2019 at 19:12

Durkee

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