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Re: Simple Q: How to give computed results from NSolve to a new

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87273] Re: Simple Q: How to give computed results from NSolve to a new
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Sun, 6 Apr 2008 06:43:01 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <ft7gfo$br6$1@smc.vnet.net>

loveinla at gmail.com wrote:

> I have solved a system of equations by NSolve. And for instance, it returns the results as 
> Root={{x->1,y->2}}.
> 
> And now I want to use the computed results, say x & y to define a new variable 
> Z=x^2+sqrt(xy).
> 
> How should I use computed x and y to define the new variable Z?

Assuming you use the correct syntax to define the variable z, you just 
have to apply the transformation rules (i.e. "something" -> "something 
else")via the replacement operator /. as in the following example:


In[1]:= sol = {{x -> 1, y -> 2}}

Out[1]= {{x -> 1, y -> 2}}

In[2]:= {x, y} /. sol[[1]]

Out[2]= {1, 2}

In[3]:= z = x^2 + Sqrt[x*y] /. sol[[1]]

Out[3]= 1 + Sqrt[2]


For more information, see

http://reference.wolfram.com/mathematica/ref/ReplaceAll.html

http://reference.wolfram.com/mathematica/tutorial/ApplyingTransformationRules.html


Regards,
-- Jean-Marc


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