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MathGroup Archive 2004

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RE : How to extract a solution from Mathematica's answer to "Solve"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49381] RE : [mg49363] How to extract a solution from Mathematica's answer to "Solve"
  • From: "Florian Jaccard" <florian.jaccard at eiaj.ch>
  • Date: Sat, 17 Jul 2004 06:38:45 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

You should write MySolution = x/.%[[1]]

But you can do it better : You can automatically obtain the assignments
x1=first solution, x2=second solution, etc. , without knowing in advance how
many solutions you have :

In[1]:=
solu = x /. Solve[(x-1)(x^2-5x+6) == 0, x]; 

In[2]:=
Do[Evaluate[ToExpression[StringJoin["x", ToString[i]]]] =
Evaluate[solu[[i]]], {i, Length[solu]}]

In[3]:=
x1

Out[3]=
1

In[4]:=
x2

Out[4]=
2

In[5]:=
x3

Out[5]=
3

regards
 
F.Jaccard


-----Message d'origine-----
De : Rainer [mailto:wilhelm.rainer at gmx.net] 
Envoyé : vendredi, 16. juillet 2004 12:07
À : mathgroup at smc.vnet.net
Objet : [mg49363] How to extract a solution from Mathematica's answer to
"Solve"

I have a question concerning the Solve command. Assume I have solved
an equation using Solve. Mathematica returns the solutions in the
following form (example for 2 solutions):

{{x->-2}, {x->2}}

Now, assume I wish always to pick the first of these two solutions and
store it in a variable (to be able to continue working with it in the
Notebook). Is there a command to "extract" the second solution and to
store it in a variable. Since the response is in a form of a matrix
{{...},{...}}, I have tried things like MySolution = %[[1]], but it
always fails.

I appreciate any helpful commands!
Thanks
Rainer




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