Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Extracting terms from an equation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69811] Re: [mg69786] Re: Extracting terms from an equation
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 23 Sep 2006 23:45:02 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

It has to do with the different levels at which x appears. FreeQ looks at multiple levels whereas MemberQ is targeted at one or more levels.

expr=a+b*x^2+c*y^2+d*x*y+e*x^3;

Cases[expr, _?(!FreeQ[#1, x]&)]

{b*x^2, e*x^3, d*x*y}

Cases[expr, _?(MemberQ[#1, x, 2]&)]

{b*x^2, e*x^3, d*x*y}

Cases[expr, _?(MemberQ[#1, x, {2}]&)]

{b*x^2, e*x^3}


Bob Hanlon

---- dimmechan at yahoo.com wrote: 
> Can someone explain the difference in the following?
> 
> Cases[a + b*x^2 + c*y^2 + d*x*y + e*x^3, _?( !FreeQ[#1, x] & )]
> {b*x^2, e*x^3, d*x*y}
> 
> Cases[a + b*x^2 + c*y^2 + d*x*y + e*x^3, _?(MemberQ[#1, x] & )]
> {d*x*y}
> 
> Thanks
> 
> Ã?Ÿ/Ã?â?? Coleman, Mark Ã?­Ã?³Ã?Â?Ã?±Ã?Ë?Ã?µ:
> > Greetings,
> >
> > I'd like to find a general way to extract all of the terms from an
> > equation that involve a given variable. For instance, consider the
> > equation
> >
> > myEquation == Exp[a + b x^2 + c y^2 + d x y + e x^3]]
> >
> > I'd like to define a function such that
> >
> >    myFunction[myEquation,x] returns the result {b x^2, d x y, e x^3}
> > 
> > Thanks,
> > 
> > -Mark
> 


  • Prev by Date: Re: Table command strange output when 'i' over 16
  • Next by Date: Re: Pure function in a pure function (again)
  • Previous by thread: Re: Extracting terms from an equation
  • Next by thread: Re: Re: Extracting terms from an equation