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MathGroup Archive 1996

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Q: How to manipulate ..

  • Subject: [mg3039] Q: How to manipulate ..
  • From: sergio at scisun.sci.ccny.cuny.edu (Sergio Rojas)
  • Date: 25 Jan 1996 05:35:41 -0600
  • Approved: usenet@wri.com
  • Distribution: local
  • Newsgroups: wri.mathgroup
  • Organization: City College Of New York - Science
  • Sender: mj at wri.com


(* 
  Hello fellows:

...................................................................... 
	Question-1:

   Starting with: 
*)

   eq1 = HoldForm[ D[k[x]*D[f[x],x],x] - h[x] == 0 ]

(* Mathematica answer:

Out[85]= D[k[x] D[f[x], x], x] - h[x] == 0

*)

(* Now one can try any form of f[x], like : *)

   u= g[x] + v[x]
   eq2= (eq1 /. {f[x]-> u, Derivative[1][f][x]->D[u,x]} )

(* Mathematica answer:

Out[89]= D[k[x] D[g[x] + v[x], x], x] - h[x] == 0

*)

(* How it can be written in the form:

-h[x] + D[k[x]*D[g[x],x],x] + D[k[x]*D[v[x],x],x] == 0

Any suggestions ?
*)

(*.................................................................... 
	Question-2:

  Suppose one have the following:  *)

  eq1 = -h[x] + D[k[x]*D[g[x],x],x] + D[k[x]*D[v[x],x],x] == 0

(* Mathematica answer:

Out[69]= -h[x] + g'[x] k'[x] + k'[x] v'[x] + k[x] g''[x] + k[x] v''[x] == 0


  How it can be told to Mathematica, write the answer in the form:

-h[x] + k'[x] (g'[x] + v'[x]) + k[x] (g''[x] + v''[x]) == 0

  or in the form:

-f[x] + k'[x] g'[x] + k[x] g''[x] + k'[x] v'[x] + k[x]  v''[x] == 0

I tried :

Simplify[eq1]
FactorTerms[eq1]
Collect[eq1,k[x]]
Together[eq1]

All of them failed.

*)

(*.................................................................... 
	Question-3

Assume one can have the form:

-f[x] + k'[x] (g'[x] + v'[x]) + k[x] (g''[x] + v''[x]) == 0

How it can be told to Mathematica, write it in the form:

-h[x] + D[k[x]*D[g[x],x],x] + D[k[x]*D[v[x],x],x] == 0

or in the form:

-h[x] + D[k[x]*D[(g[x] + v[x]),x],x] == 0

*)

(*.................................................................... 
	Question-4

 How one can save the whole Mathematical session in a edit-able file?

I know:

 Save["file",var1,var2,bla,bla,bla,..] and some variations

Dump["file"]  This can not be edited.

*)

That's all for now folks. Thanks very much for your attention.

rojas
E-mail: sergio at scisun.sci.ccny.cuny.edu

*)


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