Re: Warning Message wrt NMinimize function

*To*: mathgroup at smc.vnet.net*Subject*: [mg69760] Re: Warning Message wrt NMinimize function*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Fri, 22 Sep 2006 01:04:39 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <eeu01h$b83$1@smc.vnet.net>

John Adeosun wrote: > Hello Everyone, > > I want to use NMinimize to solve an optimization problem. In essence, I'm > trying to numerically minimize the "sum of a square of errors" for two > lists, aa and bb (earlier generated lists of n elements or points), using > the below syntax: > > NMinimize[{Plus @@ Table[(aa[[i]] - bb[[i]])^2, {i, n}], {y> 0}}, y, > Method -> "DifferentialEvolution"] > This does not yield the intended result of, say, {minimumvalue, y->10.012}. > I have been getting an expression (unevaluated "result" ) with a warning > message such as: > > NMinimize::nnum : The function value {336.381} is not a number at {y}= > {0.063703}. More... > > I then clicked on 'More' for help. I got the below message from the help > browser: > > "General::nnum > > function::nnum: The function value `3` is not a number at `2` = `1`. > > Notes for this message have not yet been added." > > Has anyone experienced this before? Is anything wrong with my syntax above? John, The syntax above seems correct (see below). I suspect you have some problem with your lists. Note that the second version of the code should be more efficient (you can do vector operations). In[1]:= aa = Table[Random[], {10}]; bb = Table[Random[], {10}]; In[3]:= NMinimize[{Plus @@ Table[(aa[[i]] - bb[[i]])^2, {i, 10}], {y > 0}}, y, Method -> "DifferentialEvolution"] Out[3]= {1.71356,{y\[Rule]13.0914}} In[4]:= NMinimize[{Plus @@ ((aa - bb)^2), {y > 0}}, y, Method -> "DifferentialEvolution"] Out[4]= {1.71356,{y\[Rule]13.0914}} In[5]:= $Version Out[5]= 5.2 for Microsoft Windows (June 20, 2005) HTH, Jean-Marc