LCLXTREM

Name

lclxtrem

Purpose

Find local minima or maxima in a 1-d vector.

Description

Scan a vector and identify all maxima or minima separated by more than
WIDTH values.

Calling Sequence

idx=lclxtrem(vec,width,[/MAXIMA])

Inputs

vec - Input vector of data points.

Optional Input Parameters

width - size of zone to search, minima (or maxima) separated by less than
width are never returned. (Default = 5)

Keyword Input Parameters

MAXIMA - Flag, if set, causes program to search for local maxima, the default
is to search for local minima

Outputs

Returns indicies into vec that give local extrema. This returned vector
is also sorted by decreasing absolute value of vec.

Keyword Output Parameters

COUNT - Number of extrema returned. If 0, there was an error.

Common Blocks

Side Effects

Restrictions

The first and last points in the array will NEVER be flagged as extrema
since there is no information to decide if the endpoint is an inflection
or not. There is one exception to this condition. If the data are
smooth and there are no inflection points, one or the other of the
endpoints will be the absolute extreme. In this case only, will an
endpoint be returned.

Procedure

This procedure scans the vector and looks for local maxima or local minima.
In the first pass, all such extrema are flagged, if you want all of them
Just set width to 0 if you want _all_ local extrema. The second pass
filters our extrema that are too close together. The width of the filter
can be provided, the default is 5. The extrema are scanned in decreasing
absolute value. For each extremum, all other extrema that are fainter and
are closer than width away are removed from the list. The returned vector
of indicies is sorted by decreasing size of the peak/trough.

Modification History

97/12/5, Written by Marc W. Buie, Lowell Observatory
99/11/24, MWB, total rewrite to speed it up and make it work properly.