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MathGroup Archive 1998

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Re: Question about equations solutions?

  • To: mathgroup at
  • Subject: [mg13164] Re: [mg13054] Question about equations solutions?
  • From: Sean Ross <seanross at>
  • Date: Mon, 13 Jul 1998 07:42:13 -0400
  • References: <>
  • Sender: owner-wri-mathgroup at

ieblanc at wrote:
> This is probably a dumb question but can anyone help.
> a = Solve[y^2+5*y*x+6*x^2==0,y]  gives an answer of  {{y->-3 x},{y->-2
> x}}
> and
> Print[a] then displays {{y->-3 x},{y->-2 x}}
> How do get Print or some later input to reference the actual solutions
> "2x" or "3x" instead of {{y->-3 x},{y->-2 x}}
> Thanks Ian

This form of output is a transformation rule.  In your case,

Map[(y/.#)&,Flatten[{{y->-3 x},{y->-2 x}},1]]

will return

{-3 x,-2 x}

and you can access the solutions as elements of the list.

The snippet of code above uses Map, from the functional paradigm along
with (y/.#)&, a pure function construct of a form from the
transformational paradigm.  I learned this mostly from third party
books on mathematica programming.  I recommend something like the Power
Programming book by David Wagner.

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