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fitting stsdas



This package contains tasks that perform function fitting operations on images, STSDAS table columns, or lists. Both linear and non-linear functions are supported.

When fitting 1-dimensional functions with input data from 2- (or more) dimensional images, the data are projected over a 1-dimensional vector before fitting the function.

The fitting tasks write their results to STSDAS tables. A common table format is used by all tasks in the package, with the same column headers and formats.

The interative linear function fitting task is gfit1d which fits Chebyshev or Legendre polynomials, linear or cubic splines, using Cholesky factorization to solve the standard least-squares normal equations.

Non-linear function fitting is split between several tasks. The first, nfit1d, interatively fits each of six different functional forms:


 * power law
 * Planck function
 * sum of two Planck functions
 * sum of a power law and a Planck function
 * galaxy brightness profile (bulge + disk)
 * user-defined function (implemented by a built-in FORTRAN interpreter)

The second task, ngaussfit, is meant to interatively fit multiple Gaussians to 1-dimensional data. The third task, n2gaussfit, is a simple non-interactive tool for fitting a 2-dimensional Gaussian to image data. Task i2gaussfit is a script useful to run n2gaussfit in noisy conditions.

The non-linear fitting can be performed by any of two algorithms, either one of which can be used to minimize chi-squared: downhill simplex (amoeba) or Levenberg-Marquardt.

There is one task to do the inverse operation, that is, to read the table with fitting results and build images, STSDAS tables or lists. Another task is available to list or print the fitting table contents in a human-readable format.


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