FIT command

Syntax: | `FIT y = { expression } FIT\UPDATE yout`
Qualifiers: | `\NORMAL, \POISSON, \UPDATE, \ITMAX, \WEIGHTS, \TOLERANCE, \ZEROS, \CHISQ, \VARNAMES, \CORRMAT, \COVMAT, \CL, \E1, \E2, \FREE, \RESET, \MESSAGES`
Defaults: | `\NORMAL, \-ITMAX, \-WEIGHTS, \-TOLERANCE, \ZEROS, \-CHISQ, \-CL, \-VARNAMES, \-CORRMAT, \-COVMAT, \-E1, \-E2, \-RESET, \-FREE, \MESSAGES`
Examples: | `FIT Y=A*X+B FIT\CHISQ\CL\ITMAX\WEIGHTS\TOLERANCE W 3 0.001 Y=A*EXP(-B*X)+C FIT\UPDATE YF`

By default, or if the `\NORMAL` qualifier is used, it is assumed that each data point has an error that is distributed as a normal distribution,

where is the mean and is the standard deviation of the distribution. The weight is defined as:

If the `\POISSON` qualifier is used, the data errors are assumed to be distributed as a Poisson distribution,

where is the mean and the variance of the distribution.

Expression and parameters

The `expression` must result in a vector with the same length as the data vector, `y`. A maximum of twenty-five (`25`) fitting parameters are allowed in the `expression`. The fitting parameter values are altered during the fit. Fit parameters are created with the `SCALAR\FIT` command, and can be converted to fixed value scalars with the `SCALAR` command. If you use the `\RESET` qualifier, the fitting parameters will be reset to their original values after an unsuccessful fit.

If the `\VARNAMES` qualifier is used with the `FIT` command, a string array variable named `FIT$VAR` will be made which will contain the names of the fitting parameter variables. The array length of `FIT$VAR` will be equal to the number of fit parameters.

Informational messages

By default, information on the progress of the fit, as well as the results, are displayed on the monitor screen. If the `\-MESSAGES` qualifier is used, these informational messages will be suppressed.

Method
Tolerance
Correlation and covariance
Confidence level
Number of iterations
Update after a fit
Normal distribution
Poisson distribution