Mathematica in conjunction with outside program; NMinimize fails. Symbolic v. numeric evaluation problem?

*To*: mathgroup at smc.vnet.net*Subject*: [mg98875] Mathematica in conjunction with outside program; NMinimize fails. Symbolic v. numeric evaluation problem?*From*: Andreas Pape <apape at binghamton.edu>*Date*: Mon, 20 Apr 2009 19:12:19 -0400 (EDT)

Hello mathgroup. I am using Mathematica in conjunction with an outside program (Netlogo is the program.) In a nutshell, my error is the following: I can call the outside program with a numeric value successfully, and Plot can call the outside program as one would expect. However, NMinimize calls the outside program with the variable name, not a value, so it fails. In short, I need to force NMinimize to pass a numeric value to the objective function, not a variable name. More details: I have the following functions defined in Mathematica: SingleModelRun[ parametervalue_ ] := ....(definition irrelevant) This function (successfully) runs the outside program, setting a parameter equal to "parametervalue" (which is some number when I call the function). It returns a value from the model. Plot[ SingleModelRun[ x ], {x , 0, 1} ] Does what you expect: runs SingleModelRun for parameter values 0 through 1, and plots the resulting return value each time. NMinimize[ - SingleModelRun[ myvalue ], {myvalue} ] Does not work. Returns the following error: NetLogo`Private`NetLogo::"compilerException" : "Nothing named MYVALUE has been defined" (Note: NetLogo is the name of the outside program.) Which means that, oddly, NMinimize passes the *variable name* (myvalue) instead of the *variable value* to the function SingleModelRun; otherwise, there is no way the outside program would be aware of the variable name. Is there a way to force Mathematica to evaluate the function with a numeric value, not the variable name? (I thought that's what "N" in "NMinimize" meant, but apparently not.) In case you were wondering, this fails in an identical way with: NMaximize, FindMaximum, FindMimimum, etc. Thank you. Sincerely, Andreas Duus Pape