NAG routines add extensive new functionality to Simfit
The academic version of Simfit is a free Windows package for simulation, curve fitting, statistical analysis and graph plotting developed by Bill Bardsley, University of Manchester, UK. It employs mathematical models from a compiled library, or from user-supplied equations, and can be used in many fields of study such as biology and psychology, and areas of work such as growth curves, factor analysis, power as a function of sample size, dose response curves, and pharmacokinetics.
At present, the NAG Library edition of Simfit uses nearly 200 numerical algorithms from NAG, and is currently being extensively enlarged in the computational areas of optimization, differential equations, curve fitting and statistics. The DLL implementation of the NAG Fortran Library is the source of the NAG algorithms used by Simfit as opposed to the public domain code used by the academic version, and this is permitting a rapid extension of Simfit functionality.
Benefits of using the NAG Library version of Simfit include:
- Higher performance implementation of BLAS and LAPACK
- The runs up and down test for randomness
- The median test
- The Mood and David tests for equal dispersions
- The Kendall coefficient of concordance
- After calculating distance matrices, classical metric scaling (principal coordinates) and non-metric scaling (calculation of STRESS and SSTRESS functions) can be done
- Multivariate factor analysis is provided
- Procrustes analysis can be performed on two loading matrices
- Varimax or Quartimax rotation can be performed on a loading matrix
- Kernel density estimates can be calculated, and then plotted against sample histograms and cumulative distribution functions
- Cross validatory splines can be fitted
- IFAIL messages are written to the file nagifail.txt, which can be browsed retrospectively in the case of failure of iterative algorithms to converge and similar problems
- There is a mechanism to demonstrate how to use the NAG Library from within the Simfit environment
More about Simfit
The Simfit package consists of some forty programs, each dedicated to a special set of functions such as fitting differential equations or specialized models, plotting, or performing statistical analysis. The package is driven from a program manager which also provides options for viewing results, editing files, using the calculator, printing files, etc. Simfit has been used for many years in postgraduate courses and students often report that it is very easy to use on account of the very extensive on-line help provided in the form of pdf with hyperlinks for easy cross-reference. Most students find they can write their own models and fit their own data within a few hours of being introduced to the package for the first time.
Simfit has wide coverage, great versatility, fast execution speed, and the ability to handle large data sets. It can perform maximum likelihood estimation, automatic calculation of starting estimates, and constrained nonlinear regression. Programmers should note that the source code is distributed with the package, along with the Simdem package, which shows programmers how to write Windows programs that can use the NAG Library.
For more information about the Simfit package, visit the Simfit page hosted by the University of Manchester.