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Re: Basic plotting of an evaluated function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86912] Re: Basic plotting of an evaluated function
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 26 Mar 2008 04:52:11 -0500 (EST)
  • Organization: Arcor
  • References: <fsa5cd$ab2$1@smc.vnet.net>

Hi,

it would be helpful
a) if you would consider to read the manual
b) use correct Mathematica syntax because
    NMinimize[{f[x,y],y=995,y=989},y]
    is remarkable nonsense

anyway

f[x_?NumericQ, y_?NumericQ] := x*(990 - y^2)

s[x_?NumericQ] := y /. Last[NMinimize[{f[x, y], y < 995, y > 989}, y]]

Plot[s[x], {x, -14, 46}]

Regards
   Jens

lederer at ssb.rochester.edu wrote:
> I am trying to do something basic--but I cannot figure it out
> 
> 
> I have some function in two varaibles
> 
> f[x_,y_]= some arbitrary polynomial
> 
> Now I want to minimize the function with respect to y over some
> compact interval with fixed x
> 
> NMinimize[{f[x,y],y=995,y=989},y]
> 
> I want to plot the y's versus the x's.
> 
> I have tried many things like defining
> 
> s[x_]=Part[NMinimize[{f[x,y],y=995,y=989},y],2]
> 
> Plot[s[x],{x,-14, 46}]
> 
> or variations
> 
> Plot[tt/.s[x],{x,-14, 46}].
> 
> Many error messages or nothing at all results.........
> 
> I am sure this is easy, and someone can suggest how to do this.
> 
> However, one more thing would be greatly helpful (give a man a decent
> and readable Mathematica manual and he can feed himself...)
> 
> I am baffled by what Mathematica wants when it comes to using a single
> part of a list and changing it to a scalar.  Suppose as above q is a
> vector with a rule assigning a value to some variable x  that is x-
>> some number, and this assignment is in the third position of the list
> 
> What is going on with  q/.d[[3]] for example: Is q now a scalar?  If
> not why  not?
> 
> Thanks for you help,
> 
> Phil Lederer
> 


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