** Up:** On the automatic folding

**Subsections**

The basic Mk IV auto-folder gives excellent folds for most rotation curves, and all of the
Mk IV solutions displayed
have been generated using from basic model.
However, for a very few individual rotation curves, it gives folds which are manifestly poor, and
the problem always manifests itself in the form of allowing the
estimated position of
to be greatly in error.
It is found that replacing the standard function-to-be-minimized,

by

where
is the calculated correction (measured in arcseconds)
to the initial estimate for the position of
,
damps the overgrowth
of
in the few pathological cases, but without having any marked
effect on the well behaved majority.

Although the PS sample contains 900 folded rotation curves, the corresponding data base
used here to develop the auto-folder only contains data for 877 (unfolded) rotation
curves.
The discrepancy of 23 rotation curves has arisen because the corresponding galaxies
were supplied with incomplete information in one of the source data-bases provided by MFB.

Of the 877 rotation curves, the auto-folder failed to fold thirteen.
Investigation showed that this was because, after choosing only
those velocities for which MFB's cross-correlation coefficient
exceeded 0.4 (see Sect. 2.1 concerning data quality)
eleven of the thirteen rotation curves concerned had no velocity
measurements on one side of the rotation curve, whilst two had only
one measurement.

** Up:** On the automatic folding

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