Introduction

XIMGFIT is a program for fitting 2D spatial data, with or without convolution of the model with a PSF image. Its command design has been modeled after XSPEC since they perform similar functions. The program is written in Python using the numerical extensions Numeric (developed at LLNL, see http://xfiles.llnl.gov/python.htm), the FFTW library (http://www.fftw.org) for very fast convolutions (although in some cases, the data and PSF images may have to be padded, as discussed below), and an extension for reading/writing fits files. As a result, the actual fitting should proceed at speeds comparable to compiled languages like C or Fortran since most of the processing is being done in these extensions. One motivation for this is that a user can modify and extend XIMGFIT, and, even if the user has no knowledge of Python, new models can be easily added without any recompilation. Of course, normal usage requires no knowledge of Python.