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Phit will fit a sum of line shapes to a real data set. The
line shapes and variable parameters used in the fit are specified by
the user. The parameters are varied using a Levenberg-Marquardt
non-linear least-squares minimization to best fit the input data. All
information needed by Phit, including the data file name, the
line shapes, and the parameter list, are supplied in a plain text input
file called phit.inp
.
Phit performs extensive error analysis including measuring
the goodness of fit and estimating error bars on the variable
parameters. This is intended to help the user interpret the fit and
extract physically significant results from the data.
Many portions of this document are copied or modified from the
document for Feffit, the XAFS fitting program written by Matt
Newville for the UWXAFS package. Phit borrows several
concepts and algorithms from that program. Chapter 5 in the
Feffit document is about goodness of fit and error analysis and
serves well as a description of those concepts for this program.
Phit, as well as this document, is intended to meet the
needs of a sophisticated user as well as a first time user. Much of
this document is a reference manual covering all of the features and
functionality of the program. Also included are several worked
examples. The first time user should read these carefully and work
through them at the computer. Sample data files and input files are
distributed with the program.
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