[Date Index]
[Thread Index]
[Author Index]
Re: Solve output depends on previous attempt with bad syntax
*To*: mathgroup at smc.vnet.net
*Subject*: [mg132512] Re: Solve output depends on previous attempt with bad syntax
*From*: Alain.Cochard at unistra.fr
*Date*: Fri, 4 Apr 2014 03:57:18 -0400 (EDT)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
*Delivered-to*: l-mathgroup@wolfram.com
*Delivered-to*: mathgroup-outx@smc.vnet.net
*Delivered-to*: mathgroup-newsendx@smc.vnet.net
*References*: <lhiuav$de5$1@smc.vnet.net>
*Reply-to*: alain.cochard at unistra.fr
Hi Kevin, and thank you very much.
Kevin writes on Thu 3 Apr 2014 06:29:
> You could have anticipated this by noting two things:
>
> (1) The symbol y1 is now black instead of blue, which means that it =
has
> a value (b+a x1) in this case;
Hum, this rather looks like an aposteriori hint! At any rate, I use
the text based interface, which has no color variations.
> (2) The use of the "=" itself is the reason.
>
> The second execution was looking for a solution to
>
> a x1 + b == a x1 +b, a x2 + b == a x2 + b
>
> Which is why you got the null answer, since a,b can be anything.
>
> To prevent this and other problems with previously used variables, I=
> would generally include
>
> Clear[a,b,x1,x2,y1,y2]
>
> in the same cell as the Solve.
OK, I see the reason now. I dare say this is a some sort of a
misconception...
Regards,
Alain
> Kevin
>
>
> On 4/3/2014 2:15 AM, Alain Cochard wrote:
> > First, the correct solution of a linear system of 2 equations with=
2
> > unknowns, for reference.
> >
> > Mathematica 9.0 for Linux x86 (64-bit)
> > Copyright 1988-2013 Wolfram Research, Inc.
> >
> > In[1]:= Solve[{y1==a x1 +b, y2==a x2 +b},{a,b}]
> >
> > -y1 + y2 x2 y1 - x1 y2
> > Out[1]= {{a -> -(--------), b -> -(-------------)}}
> > x1 - x2 x1 - x2
> >
> > Now, starting a new Mathematica session, assume I make a mistake, =
using '='
> > instead of '==', I get an error message -- so far, so good:
> >
> > Mathematica 9.0 for Linux x86 (64-bit)
> > Copyright 1988-2013 Wolfram Research, Inc.
> >
> > In[1]:= Solve[{y1=a x1 +b, y2=a x2 +b},{a,b}]
> >
> > Solve::naqs: b + a x1 && b + a x2 is not a quantified system
> > of equations and inequalities.
> >
> > Out[1]= Solve[{b + a x1, b + a x2}, {a, b}]
> >
> > Realizing my mistake, I retry with the proper syntax:
> >
> > In[2]:= Solve[{y1==a x1 +b, y2==a x2 +b},{a,b}]
> >
> > Out[2]= {{}}
> >
> > which is obviously not the correct result.
> >
> > Is there a rationale here, i.e., could I have anticipated this out=
put=3F
> >
> > Thank you,
> > Alain
> >
--
EOST (=C9cole et Observatoire des Sciences de la Terre)
IPG (Institut de Physique du Globe) | alain.cochard at unistra.fr
5 rue Ren=E9 Descartes [bureau 106] | Phone: +33 (0)3 68 85 50 44
F-67084 Strasbourg Cedex, France | Fax: +33 (0)3 68 85 01 25 =
Prev by Date:
**Re: Solve output depends on previous attempt with bad syntax**
Next by Date:
**Re: Solve output depends on previous attempt with bad syntax**
Previous by thread:
**Re: Solve output depends on previous attempt with bad syntax**
Next by thread:
**Re: Solve output depends on previous attempt with bad syntax**
| |