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MathGroup Archive 1995

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Some Easy (hopefully) Questions

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg2030] Some Easy (hopefully) Questions
  • From: Rob Carscadden <carscadd at pps.pubpol.duke.edu>
  • Date: Sat, 16 Sep 1995 01:40:17 -0400
  • Organization: Duke University, Durham, NC, USA

I'm trying to run a model using Mathematica. I've scoured all our 
libraries and all the books are gone. Working with all too basic 
Mathematica By Example, I haven't been able to find how to do some rather 
easy things.

The first thing I want to do is find a max (I need to plug the max and 
where it occurs into anther equation). I have a function, and I have 
taken both the first and second derivatives. I solve for f'(x) = 0. But 
here's where the trouble comes in. I want to plug these points back into 
my f(x). How can I do this. Look at the following example:

possmax = Solve[(x - 1)^2 == 0,x] // N

I get {{x -> 1.},{x ->1.}}
and when I try 

possmax[[1]]

I get {x ->1.} 

but I want the number 1 instead.

I know this if probably extremely basic, but due to lack of available 
documentation here, I can not figure it out.


P.S. another useful trick to know would be how many objects are in a 
list. My function a bit more complicated (compositions, logs etc.), and I 
don't exactly how many solutions I will have from the Solve[ ] statement.

-- 

Rob Carscadden                        
carscadd at pps.duke.edu                   
http://www.duke.edu/~cars
49% of all Statistics are made up on the spot!




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