## 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