benchmarking

Comparing BSXFUN and REPMAT

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问题 Few questions were asked before on comparisons between bsxfun and repmat for performance. One of them was: Matlab - bsxfun no longer faster than repmat?. This one tried to investigate performance comparisons between repmat and bsxfun , specific to performing subtraction of an input array\'s mean along the columns from the input array itself and as such would explore only the @minus part of bsxfun against its repmat equivalent. Another was : In Matlab, when is it optimal to use bsxfun?. That

How to Calculate Execution Time of a Code Snippet in C++

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I have to compute execution time of a C++ code snippet in seconds. It must be working either on Windows or Unix machines. I use code the following code to do this. (import before) clock_t startTime = clock(); // some code here // to compute its execution duration in runtime cout << double( clock() - startTime ) / (double)CLOCKS_PER_SEC<< " seconds." << endl; However for small inputs or short statements such as a = a + 1, I get "0 seconds" result. I think it must be something like 0.0000001 seconds or something like that. I remember that System.nanoTime() in Java works pretty well in this case.

Why does Python code run faster in a function?

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问题 def main(): for i in xrange(10**8): pass main() This piece of code in Python runs in (Note: The timing is done with the time function in BASH in Linux.) real 0m1.841s user 0m1.828s sys 0m0.012s However, if the for loop isn\'t placed within a function, for i in xrange(10**8): pass then it runs for a much longer time: real 0m4.543s user 0m4.524s sys 0m0.012s Why is this? 回答1: You might ask why it is faster to store local variables than globals. This is a CPython implementation detail. Remember

Why is reading lines from stdin much slower in C++ than Python?

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问题 I wanted to compare reading lines of string input from stdin using Python and C++ and was shocked to see my C++ code run an order of magnitude slower than the equivalent Python code. Since my C++ is rusty and I\'m not yet an expert Pythonista, please tell me if I\'m doing something wrong or if I\'m misunderstanding something. (TLDR answer: include the statement: cin.sync_with_stdio(false) or just use fgets instead. TLDR results: scroll all the way down to the bottom of my question and look at

What do 'real', 'user' and 'sys' mean in the output of time(1)?

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问题 $ time foo real 0m0.003s user 0m0.000s sys 0m0.004s $ What do \'real\', \'user\' and \'sys\' mean in the output of time? Which one is meaningful when benchmarking my app? 回答1: Real, User and Sys process time statistics One of these things is not like the other. Real refers to actual elapsed time; User and Sys refer to CPU time used only by the process. Real is wall clock time - time from start to finish of the call. This is all elapsed time including time slices used by other processes and

How do I write a correct micro-benchmark in Java?

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问题 How do you write (and run) a correct micro-benchmark in Java? I\'m looking for some code samples and comments illustrating various things to think about. Example: Should the benchmark measure time/iteration or iterations/time, and why? Related: Is stopwatch benchmarking acceptable? 回答1: Tips about writing micro benchmarks from the creators of Java HotSpot: Rule 0: Read a reputable paper on JVMs and micro-benchmarking. A good one is Brian Goetz, 2005. Do not expect too much from micro