Re: Another Out of Memory Problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg91314] Re: Another Out of Memory Problem*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Fri, 15 Aug 2008 06:53:06 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <g8137j$19$1@smc.vnet.net>

Kevin J. McCann wrote: > I can do the following: > > Integrate[Cos[2*x]* > Exp[I*z*Cos[x]], > {x, -Pi, Pi}] > > > which produces a Bessel function answer; however if I change the > argument in the cosine to 2.5 as in: > > Integrate[Cos[2.5*x]* > Exp[I*z*Cos[x]], > {x, -Pi, Pi}] > > I almost immediately get this: > > No more memory available. > Mathematica kernel has shut down. > Try quitting other applications and then retry. > > Any ideas why? I am running XP with 2Gb of memory. When using symbolic function (i.e. Integrate rather than NIntegrate, Solve rather than NSolve, etc.) it is always a good idea to feed the function with *exact* (infinite precision) numbers, thus 5/2 rather 2.5 in your case. (Mathematica does not find any closed form for your integrand. Note that it take a while to compute but memory consumption is under control.) In[1]:= Integrate[Cos[5/2*x]*Exp[I*z*Cos[x]], {x, -Pi, Pi}] Out[1]= I z Cos[x] 5 x Integrate[E Cos[---], {x, -Pi, Pi}] 2 Regards, -- Jean-Marc