Accessing Matlab arrays efficiently

Hi everyone,

I have a question regarding the efficiency of accessing arrays in matlab. Below you can see a screenshot taken from profiler. I thought it was a little bit surprising that lines 22-23 takes a fraction of lines 26-27. I realize that I am accessing more element of the array, however I would not expect the difference to be this much.

I would be glad if you could advise me on any methods or tricks which could be helpful to improve the efficiency?

thank you,

Murat

Answer 1

[Raunak Gupta]

Hi Murat,

As I can understand from Line 22-23, Mposition/Mvelocity are 2-D matrix and returned VpositionA/ VvelocityA are 1-D vectors. Since in Line 26-27 the same Mposition/Mvelocity is used in array indexing but here VindexB is an 1-D array rather than scalar value i, that is why the returned MpositionB/MvelocityB will be again a 2-D array rather than 1-D vector. I assume the size of VindexB is significantly greater than 1, that is why there is scaling of 10-15 times in time taken.

Here since the size of returned variable is different (1-D vs 2-D) in both set of lines, therefore we cannot compare the time taken. In my opinion if you are not thinking of using parfor then array indexing will work fine.