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FITTER Add-In for Excel™

What is FITTER?
FITTER is an Add-In procedure for Excel. If you are under Excel you can open FITTER as any add-in file using Tools/Add-Ins menu command. It will add the new menu item Fitter into Tools menu. Clicking it will activate main Fitter dialog for starting FITTER.

FITTER is a powerful instrument of statistical analysis. Using it you may solve multivariate nonlinear regression problems. Much of the power of FITTER comes from its ability to estimate parameter values of complicated user-defined functions that may be entered in ordinary algebraic notation as a set of explicit, implicit and ordinary differential equations. FITTER uses the unique procedure for analytic calculation of derivatives and special optimization algorithm which provides the high accuracy even for significantly nonlinear models. All complicated calculations are performed in the special DLL library created using C++ compiler, which provides high speed processing.

FITTER allows to include prior knowledge about parameters and accuracy of measurement in addition to experimental data. Using Bayesian estimation, you can process both unlimited arrays of single-response data, and data referring to different responses.

With the help of FITTER you can obtain a lot of additional statistical information concerning the input data and the quality of fitting. Parameter estimates, variances, covariance matrix, correlation matrix and F-matrix; the starting and final values of the sum of squares and objective function, error variance, and spread in eigenvalues of the Hessian matrix; error variance for each observation point calculated by fit and by population.

Moreover, there are hypotheses testing for: Student's test for outliers, test of series for residual correlation, Bartlett's test for homoscedastisity, Fisher's test for goodness of fit. Also, you can calculate confidence intervals for each observation point by linearization method or with the help of modified bootstrap technique.  

FITTER Approach
FITTER takes all information from open Excel workbook. Information should be placed directly on a worksheets (Data and Parameters) or written in a text box (Model). All results are also output as tables on the worksheets. In purpose to explain what information you want to use, you need to register it with the help of FITTER wizards. There are DATA, MODEL and BAYES registration wizards. While working with different FITTER wizards you only register the required information, change options and look through process of registration. You may change data only on the worksheets but not inside the wizards. Since your information (Data, Model, ...) has been registered it is kept in memory till you replace it by another registration. If you want to do some changes within the registered range of information, just write them on the worksheet. You need not register it again. Look through Example to understand FITTER approach.

FITTER Functions
All FITTER operations which are performed with the help of wizards may be done using Fitter functions too. For example, Data registration is performed by the following function.

FitterData(sDataRange:="$B$2:$F$21", sCodeString:="PRFI", kTitle:=xtYes)

Here sDataRange is the reference to the Data range, sCodeString is the code string explaining the sense of columns in the Data range (P for "predictor", R for "response" and so on). If you are accustomed with VBA programming, open new Excel module and write there the desired proceedings of function. Examples may be found in Fitter Applications.

FITTER Limits and Requirements
The following is a summary of  FITTER limitations

The maximum number of predictors, parameters, equations in the Model and data observations that FITTER can handle is limited only by the memory space provided by your system and by capacity of your computer to process complicated (multi-step) models.

FITTER can not use models containing circular interconnections of variables.

Minimum requirements to run FITTER for Windows are:
FITTER and Other NLR Tools
We made an attempt to compare FITTER with various software tools that have been designed for non-linear regression analysis. Of course we are biased, but you can download compare.zip file that contains Word 6.0 document and understand our point of view.
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Last revision 26 August 2002