Re: $Assumptions
- To: mathgroup at smc.vnet.net
- Subject: [mg92634] Re: $Assumptions
- From: Peter Breitfeld <phbrf at t-online.de>
- Date: Thu, 9 Oct 2008 06:35:00 -0400 (EDT)
- References: <gci2ia$ta$1@smc.vnet.net>
Ruth Lazkoz Sáez schrieb: > Dear all, > > I seem to be unable to change some default options globally. > > At the top of my notebook I have > > $Assumptions = {MaxRecursion -> 30, AccuracyGoal -> 10}; > > Then we I evaluate NIntegrate[Exp[-x^2], {x, 20., 40.}] > I get 4.78196*10^-176 > > But if I evaluate NIntegrate[Exp[-x^2], {x, 20., 40.}, MaxRecursion -> 30, > AccuracyGoal -> 10] > I get quite a different value, 1.36703*10^-177 > > I had the same problem trying to change the options for fonts in plots, > and then I had to add the options I wanted > in every plot, I mean evaluation something like $TextStyle ={whatever} > before doing the plots did not work. > > Hope you can help me. Thanks, > > Ruth Lazkoz > If you evaluate NIntegrate[Exp[-x^2], {x, 20, 40}, Assumptions -> True] you will get the error message: NIntegrate::optx: Unknown option Assumptions in \ NIntegrate[E^-x^2,{x,20,40},Assumptions->True]. This means, that NIntegrate doesn't have an Assumptions option. Setting $Assumtions to any value works only for functions with an Assumtions optin which must default to $Assumptions. The function Assuming works similiar to construct like this: Assuming[assum_,expr_]:=Block[{$Assumptions=assum},expr] so using Assuming won't work with NItegrate either. The following function, which I found in this group, lists all functions in the System-context, which have an Assumptions option: hatOption[option_] := ToExpression /@ Quiet[Select[Names["System`*"], MemberQ[ToExpression[#, StandardForm, Options[Unevaluated[#]] &][[All, 1]], option] &]]; hA = hatOption[Assumptions] The only function of these, which has not Assumptions->$Assumptions as default option is PowerExpand. It's Assumptions Option defaults to Automatic. So PowerExpand too will not reacht on setting $Assumptions or using Assuming. Gruss Peter -- ==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-== Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de