Re: Numerical integration and list of points

*To*: mathgroup at smc.vnet.net*Subject*: [mg87691] Re: Numerical integration and list of points*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Tue, 15 Apr 2008 06:50:20 -0400 (EDT)*Organization*: University of Bergen*References*: <ftvd4f$d89$1@smc.vnet.net> <fu1u4g$omu$1@smc.vnet.net>

guerom00 wrote: > Thank you for your answers. So this IS indeed the right method. > After some tests, it's just that my list contains 20'000 elements and > the integration takes forever to finish... > I thought Mathematica crashed because I thought it was a rather simple > thing to do but it turns out I would need to run this integration on a > powerful cluster or something :) Hi, Try using Integrate instead of NIntegrate. Integrate[] supports InterpolatingFunction objects directly, so this will be much faster than using NIntegrate[]. (I found out that Integrate can do this only because your message prompted me to experiment, so thanks for this!) Example: In[1]:= f = Interpolation@Table[{x, Sin[x^2]}, {x, 0., 20, 20/20000}]; In[2]:= Integrate[f[x], {x, 0, 20}] // Timing Out[2]= {0.25, 0.639816} Check result: In[3]:= NIntegrate[Sin[x^2], {x, 0, 20}] Out[3]= 0.639816 (Indeed, NIntegrating this takes a very long time. I haven't had the patience to wait for it to finish.) Szabolcs