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Re: Constraints to parameters in FindFit?
Jill Foley, PhD Princeton Plasma Physics Lab tel. (609) 243-0000 fax (609) 243- 0000 E-mail: <efoley at princeton.edu> Jill, You should use NMinimize, or one of the third party optimization packages, instead of FindFit (an unconstrained local optimizer). In the fcts and packages referred to, you can specify constraints on the dec vars. I am the principal developer of MathOptimizer and MathOptimizer Professional: you can see those at WR's site, also directly available from my company. For theoretical background, please see my book 'Global Optimization in Action' as well as my more recent papers. Best regards, Janos _________________________________________________ Janos D. Pinter, PhD, DSc President & Research Scientist, PCS Inc. Adjunct Professor, Dalhousie University 129 Glenforest Drive, Halifax, NS, Canada B3M 1J2 Telephone: +1-(902)-443-5910 Fax: +1-(902)-431-5100; +1-(902)-443-5910 E-mail: jdpinter at hfx.eastlink.ca Web: www.pinterconsulting.com www.dal.ca/~jdpinter Software products: http://www.pinterconsulting.com/Software_Sum_Info.pdf At 03:54 AM 10/8/2004, Jill Foley wrote: >Hi All, > >I am using FindFit to fit a series of peaks to some data. I would like >to be able to constrain some of the parameters of my fit to correspond >to physical reality. For example, some peaks should have a negative >amplitude, others positive, where the amplitudes are the parameters >that Mathematica is finding in FindFit. The peaks are all very near >each other, so without any constraint, it is making the wrong ones >negative. I'd like to specify that a given parameter should always be >negative. I am already giving an initial guess of the proper sign, but >it doesn't fix the problem. > >Please advise - Thanks! > >Jill.