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POMATLAB: Performance problem with anonymous functions
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copied!<p>Optimizing my MATLAB code, I stumbled upon a weird problem regarding anonymous functions.</p> <p>Like <a href="https://stackoverflow.com/questions/1673193/slow-performance-using-anonymous-functions-in-matlab-have-others-noticed-this">in this thread</a> I realized, that sometimes anonymous functions are running really slow. But with minimal changes to the function, it runs as fast as subfunctions or nested functions.</p> <p>I used this (simple) test file to reproduce the behaviour with Matlab R2010b under Windows 7 64-bit:</p> <pre><code>clear all; close all; clc; % functions fn1 = @(x) x^2; fn2 = @(x) double(x^2); % variables x = linspace(-100,100,100000); N = length(x); %% anonymous function y = zeros(1,N); t = tic; for i=1:N y(i) = fn1(x(i)); end tm.anonymous_1 = toc(t); %% anonymous function (modified) y = zeros(1,N); t = tic; for i=1:N y(i) = fn2(x(i)); end tm.anonymous_2 = toc(t); %% print tm </code></pre> <p>The results I got were:</p> <pre><code>tm = anonymous_1: 1.0605 anonymous_2: 0.1217 </code></pre> <p>As you can see the first approach is about 10 times slower. I have no idea what triggers this speedup/slowdown. I tried different things, getting nearly the same (fast) timings:</p> <pre><code>fn2 = @(x) 1 * x^2; fn2 = @(x) 0 + x^2; fn2 = @(x) abs(x^2); fn2 = @(x) x*x; </code></pre> <p><br/> Before I start profiling all of my functions, I would like to know if anyone has an explanation for this behaviour?</p> <p><br/> P.S.: I know that "vectorized" approaches are much faster, but in my case a solver will be evaluating the function for each variable time step, so that is not an option.</p>

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