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POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
 

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  1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
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    <p>I am getting to know some of the <code>microbenchmark</code> <code>R</code> package's featrues. I implemented a sample code from <a href="http://adv-r.had.co.nz/Performance.html" rel="nofollow">this</a> publication of Hadley Wickham and received an error I cannot find any precise information about and I cannot deal with. Thank you in advance for any explanation / hint etc. </p> <p>An example code: </p> <pre><code>library(microbenchmark) f &lt;- function() NULL microbenchmark( NULL, f() ) </code></pre> <p>Console output:</p> <pre><code>Error in microbenchmark(NULL, f()) : Measured negative execution time! Please investigate and/or contact the package author. </code></pre> <p><strong>UPDATE.</strong> Here is my <code>seesionInfo()</code> console output:</p> <pre><code>&gt; sessionInfo() R version 3.0.2 (2013-09-25) Platform: x86_64-w64-mingw32/x64 (64-bit) locale: [1] LC_COLLATE=Polish_Poland.1250 LC_CTYPE=Polish_Poland.1250 LC_MONETARY=Polish_Poland.1250 [4] LC_NUMERIC=C LC_TIME=Polish_Poland.1250 attached base packages: [1] stats graphics grDevices utils datasets methods base other attached packages: [1] ggplot2_0.9.3.1 microbenchmark_1.3-0 loaded via a namespace (and not attached): [1] colorspace_1.2-4 dichromat_2.0-0 digest_0.6.3 grid_3.0.2 gtable_0.1.2 labeling_0.2 [7] MASS_7.3-29 munsell_0.4.2 plyr_1.8 proto_0.3-10 RColorBrewer_1.0-5 reshape2_1.2.2 [13] scales_0.2.3 stringr_0.6.2 tools_3.0.2 </code></pre> <p><strong>UPDATE 2.</strong> Some further information the author of the package asked me for: </p> <ul> <li><p>R variable <code>R.version</code></p> <blockquote> <p>R.version _<br> platform x86_64-w64-mingw32<br> arch x86_64<br> os mingw32<br> system x86_64, mingw32<br> status<br> major 3<br> minor 0.2<br> year 2013<br> month 09<br> day 25<br> svn rev 63987<br> language R<br> version.string R version 3.0.2 (2013-09-25) nickname Frisbee Sailing </p> </blockquote></li> <li><p>make, model and speed of the CPU in my computer:</p></li> </ul> <p>Processor: Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz 3.70 GHz</p> <p>RAM: 16,0 GB</p> <p>System type: 64-bits </p> <p><strong>UPDATE 3.</strong> </p> <p>I have noticed that one of the modifications of the code above does return a correct result: </p> <pre><code>&gt; ### 1 &gt; f &lt;- function(){NULL} &gt; microbenchmark(NULL, f()) Error in microbenchmark(NULL, f()) : Measured negative execution time! Please investigate and/or contact the package author. &gt; &gt; &gt; ### 2 &gt; f &lt;- function(){ } &gt; microbenchmark(NULL, f()) Error in microbenchmark(NULL, f()) : Measured negative execution time! Please investigate and/or contact the package author. &gt; &gt; &gt; ### 3 &gt; f &lt;- function(){NULL} &gt; microbenchmark(f()) Unit: nanoseconds expr min lq median uq max neval f() 0 1 1 1 7245 100 &gt; &gt; ### 4 &gt; f &lt;- function(){ } &gt; microbenchmark(f()) Error in microbenchmark(f()) : Measured negative execution time! Please investigate and/or contact the package author. </code></pre>
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    1. USMarta Karas
    1. USMarta Karas
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
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      1. VTUpMod
    2. VO
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
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      1. VTUpMod
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
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      1. VTUpMod
    1. COI don't reproduce on 32 bit Ubuntu 12.04, R-devel (results of `sessionInfo()` might be helpful -- I get median times of 26 nanoseconds for `NULL` and 294 nanoseconds for `f()`. I suspect that your problem is just that the function takes so little time that there is a timing inaccuracy.
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
      1. USBen Bolker
    2. CO... I don't reproduce under MacOS X.5 R 3.0.2 either (I don't have access to a Windows system at the moment)
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
      1. USBen Bolker
    3. COThe timing function calls QPC on Windows. I do not know if your OS is calling RDTSC to fulfill QPC (some releases do). If so, and you're running an ancient multicore or multi-CPU (Core 2 or earlier), RDTSC can see time regressions when the process jumps between cores.
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      1. POWhy the 'Measured negative execution time!' error appears? (And how to deal with it?)
      1. USMatthew Lundberg
 

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