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 ]

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]} )

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

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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