[Date Index]
[Thread Index]
[Author Index]
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
Prev by Date:
**Re: Overlapping binning of differences of two lists**
Next by Date:
**Re: Overlapping binning of differences of two lists**
Previous by thread:
**Re: $Assumptions**
Next by thread:
**Re: Why is Mathematica assuming k==l and how do I make it**
| |