       Re: What's going on here??

• To: mathgroup at smc.vnet.net
• Subject: [mg33535] Re: [mg33502] What's going on here??
• Date: Fri, 29 Mar 2002 06:13:21 -0500 (EST)
• References: <11A732E5-3F06-11D6-B1D7-00039311C1CC@tuins.ac.jp>
• Sender: owner-wri-mathgroup at wolfram.com

```This is a bug affecting Simplify with assumptions of
expressions containing a==b or a!=b, with Together[a-b]==0.
Thanks for pointing it out.

Putting the following code in your init.m should fix it.

Unprotect[Simplify];

Simplify`fixrules = {
Equal[a___, b_, c___, d_, e___] :>
Equal[a, b, c, e] /; Together[b-d]===0,
Unequal[a___, b_, c___, d_, e___] :>
False /; Together[b-d]===0,
HoldPattern[Inequality[a___, b_, Equal, c_, d___]] :>
Inequality[a, b, d] /; Together[b-c]===0 };

Simplify`fixflag=True;

Simplify[a_, assum_, opts___] /;
Simplify`fixflag && !OptionQ[assum] :=
Block[{Simplify`fixflag=False},
Simplify[a/.Simplify`fixrules, assum, opts]]

Protect[Simplify];

Best Regards,

Wolfram Research

Andrzej Kozlowski wrote:
>
> This is certainly a bug. In your example c does not occur in the formula
> that is being simplified so the problem looks innocuous but a small
> modification makes it look more serious:
>
> In:=
> Simplify[5(a+a b-a(1+b))*c==0,{c>5}]
>
> Out=
> False
>
> Without the assumption there is no problem. Also,  the following give
> the correct result:
>
> In:=
> Simplify[5(a+a b-a(1+b))*c>=0,{c>5}]
>
> Out=
> True
>
> In:=
> Simplify[5(a+a b-a(1+b))*c<=0,{c>5}]
>
> Out=
> True
>
> Andrzej Kozlowski
> Toyama International University
> JAPAN
> http://platon.c.u-tokyo.ac.jp/andrzej/
>
> On Sunday, March 24, 2002, at 06:43  AM, Mat Bowen wrote:
>
> > Hello,
> >
> > I was getting weird results today and reduced the code producing them to
> > this:
> >
> > Clear[a,b,c]
> > Simplify[5(a+a b-a(1+b))==0,{c>5}]
> >
> > False
> >
> >
> > Surely thatÏ?s not right?! Can anyone explain whats going on?
> >
> > Thanks, and apologies if this is already known.
> >
> > Mat Bowen
> > Department of Mathematics
> > Loughborough University
> >
> >
> >
> >

```

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