Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1998
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1998

[Date Index] [Thread Index] [Author Index]

Search the Archive

RE: How find the max value of




barreto"@fec.unicamp.br   wrote:
 ----------
|
|w[x_,y_] := Sin[x]*Cos[y];
|
|and I need to get the max value of the function in a determinate
|interval
|
|for example
|
|
|{x,0,1},{y,-1,0}
|How can I do that?
|

Find the minimum of ( -w[x,y] ) and then change the sign.

You want to find a global minimum.  In order to do that FindMinimum
needs to  start sufficiently close to the global minimum.  Otherwise it
will likely  converge on a local minimum that isn't the global minimum.
You can do that  by sampling the function at the points on a grid, and
start at the point  where ( -w[x,y] ) is the greatest.  In the lines
below I hacked out some  code to do this.  If you like you can
implement this in a package.

In the lines below use it my code on a less trivial example. For this
example FindMinimum would have worked if it started at almost any 
point in the given interval.  For other examples it will be more
important  to sample at the points in a grid.

Ted Ersek
_______________________________

In[1]:=
w[x_,y_] := Sin[x+Pi/3]*Cos[y+Pi/3]/(x^2+1/2)

In[2]:=
Module[{pnts, z, biggest, index, start, result}, (
   pnts=Table[{x,y,w[x,y]},{x,0,2,0.1},{y,-2,0,0.1}];
   pnts=Flatten[pnts,1];
   z=Part[Transpose[pnts],3];
   biggest=Max[z];
   index=Position[pnts,biggest];
   index=Part[index,1,1];
   start=Part[pnts,index];
   result=FindMinimum[-w[x,y],{x,start[[1]]},{y,start[[2]]}];
   result/.{dip_,xyvalues_}->{-dip,xyvalues}
 )]


Out[2]=
{1.788104802108598, {x -> 0.1118975014816867,
   y -> -1.047197650578143}}




  • Prev by Date: Output from StringForm
  • Next by Date: RE: Differential Equations
  • Prev by thread: Output from StringForm
  • Next by thread: Re: RE: How find the max value of