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MathGroup Archive 1998

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Re: Getting rid of annoying zeroes in algebraic expressions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15234] Re: Getting rid of annoying zeroes in algebraic expressions
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 27 Dec 1998 03:58:27 -0500
  • References: <75q1n1$23s@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Sean:

What about using Chop?

xx=0. + (a*f)/(0. + f) + (b*f)/(0. + f) + (c*f)/(0. + f)

    0. + (a*f)/(0. + f) + (b*f)/(0. + f) + (c*f)/(0. + f)


Chop[%]

    a+b+c

Allan,
---------------------
Allan Hayes
Mathematica Training and Consulting
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565


Ross, Sean wrote in message <75q1n1$23s at smc.vnet.net>...
>
>Let xx be the result of some algebraic manipulations which, for some
>reason, mathematica thinks the real zeroes ought to be kept and I think
>they ought to be dropped.
>
>xx=0. + (a*f)/(0. + f) + (b*f)/(0. + f) + (c*f)/(0. + f)
>
>xx/.Plus[0.,q_]->q
>
>returns
>
>0. + (a*f)/(0. + f) + (b*f)/(0. + f) + (c*f)/(0. + f)
>
>while
>
>0. + (a*f)/(0. + f) + (b*f)/(0. + f) + (c*f)/(0. + f)/.Plus[0.,q_->q]
>
>returns the expected
>
>a+b+c.
>
>xx is supposed to be equivalent to the expression, but in this case, it
>is not.
>I can't write a function to automatically drop zeroes if expressions
>behave differently when they are alone on an input line and when they
>are set equal to a symbol.  Does anyone know how to eliminate this kind
>of behavior?  I am sure it has something to do with some obscure step
>in the "standard evaluation cycle" and that there is probably a long,
>convoluted explanation as to why someone would want this behavior, but
>I don't and I would appreciate it if someone could tell me how to get
>rid of it or circumvent it.
>
>Thanks,
>
>Sean Ross
>
>Please reply to rosss at plk.af.mil as I no longer subscribe to the
>mathgroup.
>
>



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