MATLAB®

Analyzing Your Program's Performance

Overview

The M-file Profiler graphical user interface and the stopwatch timer functions enable you to get back information on how your program is performing and help you identify areas that need improvement. The Profiler can be more useful in measuring relative execution time and in identifying specific performance bottlenecks in your code, while the stopwatch functions tend to be more useful for providing absolute time measurements.

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The M-File Profiler Utility

A good first step to speeding up your programs is to find out where the bottlenecks are. This is where you need to concentrate your attention to optimize your code.

The MATLAB^® software provides the M-file Profiler, a graphical user interface that shows you where your program is spending its time during execution. Use the Profiler to help you determine where you can modify your code to make performance improvements.

To start the Profiler, type profile viewer or select Desktop > Profiler in the MATLAB Command Window. See Profiling for Improving Performance in the MATLAB Desktop Tools and Development Environment documentation, and the profile function reference page.

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Stopwatch Timer Functions

If you just need to get an idea of how long your program (or a portion of it) takes to run, or to compare the speed of different implementations of a program, you can use the stopwatch timer functions, tic and toc. Invoking tic starts the timer, and the first subsequent toc stops it and reports the time elapsed between the two.

Use tic and toc as shown here:

tic
   -- run the program section to be timed --
toc

Keep in mind that tic and toc measure overall elapsed time. Make sure that no other applications are running in the background on your system that could affect the timing of your MATLAB programs.

Measuring Smaller Programs

Shorter programs sometimes run too fast to get useful data from tic and toc. When this is the case, try measuring the program running repeatedly in a loop, and then average to find the time for a single run:

tic
   for k = 1:100
      -- run the program --
   end
toc

Using tic and toc Versus the cputime Function

Although it is possible to measure performance using the cputime function, it is recommended that you use the tic and toc functions for this purpose exclusively. It has been the general rule for CPU-intensive calculations run on Microsoft^® Windows^® machines that the elapsed time using cputime and the elapsed time using tic and toc are close in value, ignoring any first time costs. There are cases however that show a significant difference between these two methods. For example, in the case of a Pentium 4 with hyperthreading running Windows, there can be a significant difference between the values returned by cputime versus tic and toc.

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Performance

Techniques for Improving Performance