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MathGroup Archive 1992

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Inequalities posting: Convert1.m

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Inequalities posting: Convert1.m
  • From: mstankus at oba.ucsd.edu (Mark Stankus)
  • Date: Fri, 20 Nov 92 11:25:30 PST

(* :Title: 	Convert1 // Mathematica 2.0 *)

(* :Author: 	Mark Stankus (mstankus).
                Based on the work of David Hurst (dhurst)
                in the file NCTools.m 
*)

(* :Context: 	Convert1` *)

(* :Summary:
		Convert1 is similar to Convert1, but only works
                for commutative expressions. Convert1 does
                not depend on any NCAlgebra code.
*)

(* :Alias:
*)

(* :Warnings: 
*)

(* :History: 
   :8/26/92     Wrote code. (mstankus)
   :10/18/92    Adapted Convert1 from Convert2. (mstankus)
*)
BeginPackage["Convert1`"];

Clear[Convert1];

Convert1::usage = 
     "Convert1[expr] is a variant of Convert1[expr] which is \
      recursive and follows a slightly different ordering.";
 
Begin["`Private`"];

(*
      Change input given in the wrong format to the
      correct format with a head of Equal.
*)
Convert1[x_Plus] := Convert1[x==0];

Convert1[x_Rule] := Convert1[x[[1]]==x[[2]]];

Convert1[x_RuleDelayed] := Convert1[x[[1]]==x[[2]]];

Convert1[x_List] := Map[Convert1,x];

Convert1[True] := 
Module[{},
    Print["Warning from Convert1: Converting True"];
    Return[0->0]
];

Convert1[False] := 
Module[{},
    Print[" :-( Severe Warning from Convert1: Converting False"];
    Abort[];
    Return[0->0]
];

(* 
      The important code.
*)
Convert1[x_Equal]:= Convert1[Equal[x[[1]]-x[[2]],0]] /; Not[x[[2]]===0]

Convert1[x_Equal]:=
Module[{expr,expr2,orderedlist,left,right,coeff,
        var,temp},
     expr = Expand[x[[1]]];
     If[Head[expr]===Plus,expr2 = Apply[List,expr];
                         ,expr2 = {expr};
     ];
     orderedlist = Sort[expr2];
     left = orderedlist[[-1]];
     right = -expr + left;
     If[Head[left]==Times, coeff= left[[1]];
                           left = left/coeff;
                           right = right/coeff;
     ];
     var = Unique[];
     temp = right/.left->right;
     If[Not[FreeQ[temp,var]], 
           Print["Using the rule ",left->right];
           Print["leads to an infinite loop."];
     ];
     Return[left->right]
] /; x[[2]]===0

End[];
EndPackage[]





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