SPIFIT-Fits a global polynomial to a spiketrum to form a spectrum

Description:

SPIFIT interpolates between the points of a 'spiketrum' - an array where most of the data is zero except for a few elements whose values are set - to produce a spectrum. Interpolation is by fitting a global polynomial to the data points.

Parameters:

SPIKETRUM

The name of the spiketrum - an array where only a few elements are set to the correct values, the other elements all being zero - which is to be used to produce a spectrum by interpolation between those specified elements. SPIKETRUM has probably been produced by GSPIKE from a table of values.

ORDER

The order of polynomial to be fitted to the points of the spiketrum.

SPECTRUM

The name of the spectrum to be produced by interpolation between the points of the spiketrum.

LOG

It doesn't usually make much difference whether you fit to the log of the data or to the data itself, but if the data is changing very rapidly, particularly at the ends, the fit may be better constrained if the log is used.

Source comments:

 I N T E R P    /     S P I F I T    /   L I N T E R P

 Interpolates between the points of a 'spiketrum' to
 generate a spectrum.   The INTERP command does this by
 spline interpolation, the SPIFIT command uses global polynomial
 fitting, and the LINTERP command uses linear interpolation.

 Command parameters -

 SPIKETRUM  The name of the structure containing the spiketrum

 ORDER      The order for the global polynomial to be fitted
            (SPIFIT only).

 SPECTRUM   The name of the result of the operation.  This can
            be the same as for SPIKE.  If not, a new structure
            is created, with everything but the data a direct
            copy of the input.

 Command keywords  -

 LOG        (INTERP & SPIFIT only) Perform the interpolation on
            the log of the data

 LINEND     (INTERP only) Use a linear interpolation for the
            ends of the data - spline fits can go wild outside the
            range of the defined points.

 User variables used - None
                                  KS / CIT 6th July 1984