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Groups > comp.soft-sys.math.mathematica > #16719

Solve output depends on previous attempt with bad syntax

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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 output?

Thank you,
Alain

-- 
EOST (École et Observatoire des Sciences de la Terre) 
IPG (Institut de Physique du Globe) | alain.cochard@unistra.fr
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F-67084 Strasbourg Cedex, France    | Fax:   +33 (0)3 68 85 01 25     

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Solve output depends on previous attempt with bad syntax Alain Cochard <Alain.Cochard@unistra.fr> - 2014-04-03 06:15 +0000
  Re: Solve output depends on previous attempt with bad syntax Kevin <kjm@KevinMcCann.com> - 2014-04-04 07:57 +0000
  Re: Solve output depends on previous attempt with bad syntax Alain.Cochard@unistra.fr - 2014-04-04 07:57 +0000

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