Groups > comp.soft-sys.math.mathematica > #2668

Re: get a, b from numbers in the form a+b Pi

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From	Murray Eisenberg <murray@math.umass.edu>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: get a, b from numbers in the form a+b Pi
Date	Tue, 24 May 2011 09:57:59 +0000 (UTC)
Organization	Steven M. Christensen and Associates, Inc and MathTensor, Inc.
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The code fails to give a pair {a,b} in case the list nums includes a 
Pi-free number, e.g., 2.


On 5/23/2011 6:28 AM, Peter Breitfeld wrote:
> "1.156" wrote:
>
>> I have lists  of numbers (Mathematica output) all numerically in the
>> form a + b*Pi and I'm trying to extract the values of a and b for
>> further work.
>>
>> Here's an example of the best I've been able to do so far:
>>
>> nums={1/2 (-2+\[Pi]),-2+(3 \[Pi])/4,-(11/3)+(5 \[Pi])/4,5/48 (-64+21
>> \[Pi]),-(61/5)+(63 \[Pi])/16,-(338/15)+(231 \[Pi])/32};
>> {FullForm[#][[1,1]],FullForm[#][[1,2]]/\[Pi]}&/@nums
>>
>> When I run this line of code 4 of the six input numbers give me the
>> {a,b} I'm looking for but the first and fourth entries fail because the
>> form isn't right. Possibly I could patch this scheme to look for a small
>> finite set of possibilities of input number form but I suspect I may a
>> long way from attacking this problem correctly.
>>
>> Can someone offer some other ideas on how to pull this off? Many thanks
>> for looking at this. Rob
>> --
>> Sent from my plain desktop PC.
>>
>
> Try this:
>
> abRule = a_. + b_. Pi :>  {a, b}
> Expand[nums]
> % /. abRule


-- 
Murray Eisenberg                     murray@math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

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Re: get a, b from numbers in the form a+b Pi Murray Eisenberg <murray@math.umass.edu> - 2011-05-24 09:57 +0000
  Re: get a, b from numbers in the form a+b Pi Peter Breitfeld <phbrf@t-online.de> - 2011-05-25 09:56 +0000

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