MATLAB: Optimize the end statement in a for loop

for loopperformance

I have a loop that runs millions of times that cannot be arrayed. Using the profiler I've noticed some of the lines that take up the most time are the end statements. Are there any ways to make the end statement of the for loop more efficient such as preallocation of single variables or clearing variables before the end of a loop?

Best Answer

The "end" statement itself does not take any time, but when MATLAB needs some time to do internal operations for the loop, the time is sometimes marked as being on the "end" because it is not really directly associated with the other lines.

You should, in particular, pre-allocate any arrays that you write inside of. However, arrays that you overwrite completely without any subscripts, do not need to be preallocated.

clearing variables before the end of the loop is, in most cases, not necessary and could slow you down. There are some cases where it helps.

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MATLAB: How to speed up the while loops

Why do you assume, that the while loop needs a remarkable amount of time in your code? The profiler will reveal, which lines or subfunctions require the most time. When the loop itself takes a few percent of the processing time only, an optimization is not efficient.

Matlab's JIT acceleration is impeded, if lines contain more than one command. Therefore and to improve the readability, use one command per line only.

MATLAB: Trying to reduce computation time

Pre-allocation the output before the loop:

Value1 = zeros(1, n);
Value2 = zeros(1, n);

I do not expect, that this is the bottleneck. But the costs of a forgotton pre-allocation grow exponentially, such that there is a limit in the input size, where this becomes the bottleneck.

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MATLAB: Trying to reduce computation time

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