STScI Logo

userpars stsdas.analysis.fitting


NAME · USAGE · PARAMETERS · EXAMPLES · BUGS · SEE_ALSO

NAME

userpars -- Edit parameters for fitting a user-defined function.

USAGE

userpars

PARAMETERS

(function) [string]
The functional form to be fitted, written as a FORTRAN expression. If the string begins with the character "@", the remaining part of the string is taken as a file name which actually contains the FORTRAN function, written in free-format. All FORTRAN operators and intrinsic functions, including the relational operators, are supported. Comments can be embedded in the function: everything between a # character and the end of the line is discarded by the interpreter. Only two types of variable names are recognized: the character "x", meaning the independent variable vector; and the function coefficients "c1", "c2", etc.. For more information on this facility, type help funcform.
(cthrough c10= INDEF) [real]
Initial guess for the first function coefficient is c1, subsequent coefficients are ci where i is the number from 1 through 10.
(vthrough v10= no) [boolean]
Vary coefficients 1 through 10 ? The first coefficient is varied by specifying v1 = yes, the second by specifying v2 = yes, etc.

EXAMPLES

1 - Fit function y = c1 * (c2/x) ** (x/2.) + 1.25 to data in file data, with results stored in out table.


fi> userpars.function = "c1 * (c2/x) ** (x/2.) + 1.25"
fi> userpars.c1 = 1.0
fi> userpars.c2 = 3.e4
fi> userpars.v1 = yes
fi> userpars.v2 = yes
fi> nfit1d  data out  func="user"

2 - Fit black-body function to data in file data, with results stored in out table. The functional form is stored in file bbfunction.


fi> type bbfunction
# Black body function
#
# c1  -  temperature
# c2  -  intensity at reference wavelength
# c3  -  reference wavelength in Angstroms

c2 *
((c3 ** 5) * (exp (1.438786e8 / c1 / c3) - 1.)) /
(( x ** 5) * (exp (1.438786e8 / c1 / x ) - 1.))


fi> userpars.function = "@bbfunction"
fi> userpars.c1 = 5000.
fi> userpars.c2 = 3.e-14
fi> userpars.c3 = 5500.
fi> userpars.v1 = yes
fi> userpars.v2 = yes
fi> userpars.v3 = no
fi> nfit1d  data out  func="user"

BUGS

SEE ALSO

nfit1d, funcform


Package Help · Search Form · STSDAS