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Re: problems with parameter lumping using ReplaceAll

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105880] Re: problems with parameter lumping using ReplaceAll
  • From: dh <dh at metrohm.com>
  • Date: Wed, 23 Dec 2009 02:40:58 -0500 (EST)
  • References: <hgq26v$gck$1@smc.vnet.net>


Hi Sean,

if you do not end: sol=... by a semicolon, mathematica prints the result 

of sol=.... Therefore, first you see the un-replaced expression and only 

afterwards the replaced one.

Daniel



sean wrote:

> Hello Group,

> 

> I have a pretty nasty expression that I'm trying the lump the

> parameters for.

> 

> I'm having problems making mathematica perform the following

> replacement.

> Like I said it's pretty nasty and hope it pastes ok.

> 

> sol = {{C[0]->p/(-4 a+4 b)+(Sqrt[l^2-m] vd)/(-4 a+4 b)-Sqrt[u-v-2 Sqrt

> [l^2-m] q vd-2 Sqrt[l^2-m] r vd]/(-4 a+4 b),M[0]->-(i/(2 V1-2 V2))-j/

> (2 V1-2 V2)+Sqrt[s^2-4 t]/(2 V1-2 V2)+V1/(2 V1-2 V2)-V2/(2 V1-2 V2),X

> [0]->l/(2 V3-2 V4)+Sqrt[l^2-m]/(2 V3-2 V4)},{C[0]->p/(-4 a+4 b)+(Sqrt

> [l^2-m] vd)/(-4 a+4 b)-Sqrt[u-v-2 Sqrt[l^2-m] q vd-2 Sqrt[l^2-m] r vd]/

> (-4 a+4 b),M[0]->i/(-2 V1+2 V2)+j/(-2 V1+2 V2)+Sqrt[s^2-4 t]/(-2 V1+2

> V2)-V1/(-2 V1+2 V2)+V2/(-2 V1+2 V2),X[0]->l/(2 V3-2 V4)+Sqrt[l^2-m]/(2

> V3-2 V4)},{C[0]->p/(-4 a+4 b)+(Sqrt[l^2-m] vd)/(-4 a+4 b)+Sqrt[u-v-2

> Sqrt[l^2-m] q vd-2 Sqrt[l^2-m] r vd]/(-4 a+4 b),M[0]->-(i/(2 V1-2 V2))-

> j/(2 V1-2 V2)+Sqrt[s^2-4 t]/(2 V1-2 V2)+V1/(2 V1-2 V2)-V2/(2 V1-2 V2),X

> [0]->l/(2 V3-2 V4)+Sqrt[l^2-m]/(2 V3-2 V4)},{C[0]->p/(-4 a+4 b)+(Sqrt

> [l^2-m] vd)/(-4 a+4 b)+Sqrt[u-v-2 Sqrt[l^2-m] q vd-2 Sqrt[l^2-m] r vd]/

> (-4 a+4 b),M[0]->i/(-2 V1+2 V2)+j/(-2 V1+2 V2)+Sqrt[s^2-4 t]/(-2 V1+2

> V2)-V1/(-2 V1+2 V2)+V2/(-2 V1+2 V2),X[0]->l/(2 V3-2 V4)+Sqrt[l^2-m]/(2

> V3-2 V4)},{C[0]->p/(-4 a+4 b)-(Sqrt[l^2-m] vd)/(-4 a+4 b)-Sqrt[u-v+2

> Sqrt[l^2-m] q vd+2 Sqrt[l^2-m] r vd]/(-4 a+4 b),M[0]->-(i/(2 V1-2 V2))-

> j/(2 V1-2 V2)+Sqrt[s^2-4 t]/(2 V1-2 V2)+V1/(2 V1-2 V2)-V2/(2 V1-2 V2),X

> [0]->f/(-2 V3+2 V4)+g/(-2 V3+2 V4)+Sqrt[l^2-m]/(-2 V3+2 V4)-V3/(-2

> V3+2 V4)+V4/(-2 V3+2 V4)},{C[0]->p/(-4 a+4 b)-(Sqrt[l^2-m] vd)/(-4 a+4

> b)-Sqrt[u-v+2 Sqrt[l^2-m] q vd+2 Sqrt[l^2-m] r vd]/(-4 a+4 b),M[0]->i/

> (-2 V1+2 V2)+j/(-2 V1+2 V2)+Sqrt[s^2-4 t]/(-2 V1+2 V2)-V1/(-2 V1+2

> V2)+V2/(-2 V1+2 V2),X[0]->f/(-2 V3+2 V4)+g/(-2 V3+2 V4)+Sqrt[l^2-m]/

> (-2 V3+2 V4)-V3/(-2 V3+2 V4)+V4/(-2 V3+2 V4)},{C[0]->p/(-4 a+4 b)-(Sqrt

> [l^2-m] vd)/(-4 a+4 b)+Sqrt[u-v+2 Sqrt[l^2-m] q vd+2 Sqrt[l^2-m] r vd]/

> (-4 a+4 b),M[0]->-(i/(2 V1-2 V2))-j/(2 V1-2 V2)+Sqrt[s^2-4 t]/(2 V1-2

> V2)+V1/(2 V1-2 V2)-V2/(2 V1-2 V2),X[0]->f/(-2 V3+2 V4)+g/(-2 V3+2

> V4)+Sqrt[l^2-m]/(-2 V3+2 V4)-V3/(-2 V3+2 V4)+V4/(-2 V3+2 V4)},{C[0]->p/

> (-4 a+4 b)-(Sqrt[l^2-m] vd)/(-4 a+4 b)+Sqrt[u-v+2 Sqrt[l^2-m] q vd+2

> Sqrt[l^2-m] r vd]/(-4 a+4 b),M[0]->i/(-2 V1+2 V2)+j/(-2 V1+2 V2)+Sqrt

> [s^2-4 t]/(-2 V1+2 V2)-V1/(-2 V1+2 V2)+V2/(-2 V1+2 V2),X[0]->f/(-2

> V3+2 V4)+g/(-2 V3+2 V4)+Sqrt[l^2-m]/(-2 V3+2 V4)-V3/(-2 V3+2 V4)+V4/

> (-2 V3+2 V4)}}

> 

> sol//. 2 V1-2 V2-> 2w/. 2 V3-2 V4 -> 2x//Simplify

> 

> If you try it, 2 V1- 2 V2  is only replaced in every other denominator

> in the solutions. (There are 8 equilibrium points in the sol up there)

> 

> It also fails to recognize that -V1 + V2 is -w.

> 

> Similarly, 2 V3-2 V4 -> 2x  fails to replace in some of the

> expressions.

> 

> It seems like it has to do with - sign in front of the expression that

> mathematica is trying to make the replacements into. If the expression

> contains the - sign, it doesn't replace the expression.

> 

> Question is how do I make the replacements regardless the sign?

> 

> 

> Thanks much in advance.

> 

> Sean

> 




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