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Strange quirk to FindMinimum

  • To: mathgroup at
  • Subject: [mg8454] Strange quirk to FindMinimum
  • From: "K. Nikolaj Berntsen" <knb at>
  • Date: Sat, 30 Aug 1997 00:43:08 -0400
  • Organization: News Server at UNI-C, Danish Computing Centre for Research and Education.
  • Sender: owner-wri-mathgroup at

In Mathematica 3.0 I try to minimize a function. I run into some
problems which probably can be avoided by renaming the variables, but I
think that it is puzzling enough to post it to this group. By the way,
thanks to all the people who helped me get rid of outer braces by.

In[]:=	f = Log[\[Lambda]]^2 + x[1]^2;
In[]:=	FindMinimum[Evaluate[f],{x[1],1},{\[Lambda],2}]
Out[]:=	{6.47493078439917812`*^-19, {x[1] \[Rule]
      \[Lambda] \[Rule] 0.999999999198761813`}}

Really nice and neat. Then I remove the square of the x[1]:

In[]:=	f = Log[\[Lambda]]^2 + x[1];
In[]:=	FindMinimum[Evaluate[f],{x[1],1.},{\[Lambda],2.}]
error:	Function::"flpar": Parameter specification {x[1], \[Lambda]} 
	in Function[{x[1], \[Lambda]}, Log[\[Lambda]]^2 + x[1]] should be a
	symbol or a list of symbols.

Hm. that really doesn't make any sense to me.

Now I change x[1] to x and \[Lambda] to y:

In]}:=	f = Log[y]\^2 + \ x;
In[]:=	FindMinimum[Evaluate[f],{x,1.},{y,2.}]
error:	FindMinimum::"fmnum": Objective function -13.43 + 1.07 I
	is not real at {x, y} = {-3.59,-1.18}
Out[]:=	FindMinimum[Evaluate[f],{x,1.},{y,2.}]

This is a reasonable answer from mathematica I think, so I will try and
change my fancy greek variable names to latin ones. But if any of you
can understand it I will appreciate the insight. Otherwise I might send
it to Wolfram.

Happy Computing,
| Ph.D. stud., cand.scient.				     |
| K. Nikolaj Berntsen					     |
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