Re: [Genesis-sim-users] Weird arithmetic error in Genesis

[Jaeger, D. <dj...@em...>]

I think you overflowed your integer welcome.   If you shorten your numbers by a few digits you will do much better.  Of course forcing to float is even better.  Not sure where the digits that an int can’t hold actually go.  It could be bad, i.e. random memory overwrite.  -Dieter

From: Cengiz Günay [mailto:cg...@em...]
Sent: Wednesday, July 22, 2015 4:49 PM
To: gen...@li...
Subject: [Genesis-sim-users] Weird arithmetic error in Genesis

Hi,
I have been pulling my hair trying to debug arithmetic inconsistencies in Genesis that are caused by large truncation errors from simplest calculations and inconsistent PI definitions, which I realize have been known and we need to be cautious about. However, I wanted to report something really disturbing:

> echo { 2012303744.1 / 3658733824.0 }
0.5500000385
> echo { 2012303744.1 / 3658733824 }
0.9370519524
Does anyone have an explanation for this behavior? This can cause seriously wrong calculations and hidden bugs.

I think the take home message is to always put a .0 behind integer numbers that are going to be in floating point calculations. :)
Best,
-Cengiz

--
Cengiz Gunay
Postdoctoral Fellow, Dept. of Biology
Visiting Faculty, Dept. of Math & CS
Emory University
http://www.biology.emory.edu/research/Prinz/Cengiz/

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