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Re: ode15s different step required at other compuer

From: Carlo De Falco
Subject: Re: ode15s different step required at other compuer
Date: Mon, 23 Dec 2019 16:53:03 +0000

> Il giorno 20 dic 2019, alle ore 23:57, Lysandros Anastasopoulos (NTUA) 
> <address@hidden> ha scritto:
> Hello together,
> in order to numerically integrate a stiff differential equation of motion 
> (ca. 30 degrees of freedom), I am resorting to the ode15s in octave since I 
> have the privilege to execute it via batch script on a remote, high 
> performance computer. However, I notice something strange: the exact same 
> ODE, with the same ode-settings, requires much more simulation steps on the 
> remote computer than on my notebook. What could the reason be? (Even the same 
> odepkg is used)
> Thanks and nice Xmas days
> Lysandros


ode15s does not require, nor use in any way, any function from the odepkg 
so the fact that you have the same version of odepkg installed on both machines 
is irrelevant.

ode15s is implemented as wrapper around ode15i, which, in turn, is just an 
to the SUNDIALS-IDA solver [1]. Depending which version of Octave you are using,
different versions of SUNDIALS-IDA can be linked to, and even the same version
may be built with different options, so you may want to look at build options 
for sundials
on the different machines to understand the different behaviour.


P.S. : I am not sure how big a performance gain you can expect by running on "a 
remote, high performance computer", 
if the "high performance" is related to parallelism, 30 dofs may be way too 
small a system to actually expolit that
And, in any case, the ode15s interface only uses the sequential version of 
sundials-ida ...


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