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MathGroup Archive 2000

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Re: Factor MatrixForm

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21405] Re: Factor MatrixForm
  • From: Gianluca Gorni <gorni at dimi.uniud.it>
  • Date: Tue, 4 Jan 2000 02:12:36 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

I already thought about how to format a symbolic list or matrix with
a common factor collected out, and I solved it by using PolynomialGCD[]
and PrecedenceForm[].

My full code is here (the variable names are an Italian/English hybrid):

collectFactorFromLists[exprList_List] :=
 Module[{fatt, sempl},
  fatt = PolynomialGCD @@ Flatten[{exprList}];
  If[StringMatchQ[ToString[InputForm[fatt]], "-*"],
    fatt = -fatt];
  sempl = If[fatt =!= 0, Simplify[Expand[exprList/fatt]]];
  If[fatt === 0 || fatt === 1,
    If[ByteCount[exprList] < 500,
       MatrixForm[exprList], exprList],
    PrecedenceForm[Simplify[fatt], 1]*
      PrecedenceForm[If[ByteCount[sempl] < 500 && MatrixQ[sempl],
        MatrixForm[sempl], sempl]]]];

collectFactorFromLists[expr_ /; Head[expr] =!= List] := expr;

When you want to use the output for further calculations,
you have do deformat it first by applying the rules
PrecedenceForm[a_,___]:>a and MatrixForm -> Identity.

Good luck.

                      Gianluca Gorni
-- 


 +---------------------------------+
 | Gianluca Gorni                  |
 | Universita` di Udine            |
 | Dipartimento di Matematica      |
 |   e Informatica                 |
 | via delle Scienze 208           |
 | I-33100 Udine UD                |
 | Italy                           |
 +---------------------------------+
 | Ph.: (39) 0432-558422           |
 | Fax: (39) 0432-558499           |
 | mailto:gorni at dimi.uniud.it      |
 | http://www.dimi.uniud.it/~gorni |
 +---------------------------------+



> a list in MatrixForm, something like this:
>
>  MatrixForm[t]
>
>  [ Cos[a]Sin[b]H - Sin[a]Sin[b]H ]
>  [ -Sin[a]k*w*H - 5*Sin[b]*k*H   ]
>  [   -2Cos[2a]H                  ]
>
> What manipulation do I perform to get it to look like
>
>    [ Cos[a]Sin[b] - Sin[a]Sin[b] ]
>  H*[ -Sin[a]k*w - 5*Sin[b]*k     ]
>    [ -2Cos[2a]                   ]
>
>
>
> --
> ----------------------------------------------------------------
>  Bob Love
>  rlove at neosoft.com
> ----------------------------------------------------------------



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