PROCESS STK
                          ------- ---

Parameters, alphabetically:
panel     trim      trimin    trimout


UPDATES:   Version 2013.4 corrected TRIMOUT and TRIMIN.  They were 
           incorrect (wrong) probably since Jan 2010.

Document Date: 16 July 2013 (removed parameter XXT - range varying stack))

PROCESS STK contains several alternative algorithms for stacking
(summing) traces.  These stacking algorithms could not be options
of PROCESS STACK because they require the entire "gather" before
the summation can start.  Recall that a "gather" is a set of traces
where the last trace of the "gather" has the special SIOSEIS
end-of-gather flag (header word 51 set to -1).  The end-of-gather
flag may be set by PROCESS GATHER, processes INPUT or DISKIN
parameter NTRGAT, or PROCESS HEADER.

A TRIM stack is a MEDIAN stack where a percentage of the trace values
relative to the median value are summed.  For each time sample, all
traces values within the gather are examined and the median value
is determined by sorting the values.  See parameters TRIMOUT and
TRIMIN for further explanation.

A stack PANEL is a progressive stack; each trace within the gather
is added to the stack and the partial stack is output.  There will
be as many stacked traces as there are input traces.  e.g. Output
trace 1 is just one trace, trace 2 is the sum of trace 1 + 2,trace 3
is the sum of trace 1 + 2 + 3, etc
    
PARAMETER DICTIONARY
--------- ----------

TRIM   - The TRIM percent of trace values furthest from the median
TRIMOUT  value are excluded (trimmed off) from the stack.  The percentage
         is of the total number of traces in the gather,  e.g. 
         trim 30 means 30% of the traces are trimmed off (excluded)
         each side of the median.  If there are 10 traces in the gather
         only the middle 4 values are included in the stack: the outer
         3 values on each side of the median excluded from the stack.
         e.g. TRIMOUT 40 and 10 traces, then only 2 values are stacked.
         PRESET = 0.

TRIMIN - The TRIMIN percent of trace values closet to the median
         value are excluded (trimmed off) in the stack.  The TRIMIN
         percent of trace values furthest from the median are 
         included in the stack.  TRIMIN and TRIM are mutually exclusive.
         e.g. With 10 traces in the gather and TRIMOUT 20, then only the
         middle 4 trace values are included.
         PRESET = 0.

PANEL  - When set non-zero, a progressive stack panel is produced.
         Preset = 0.        e.g.    panel 1

END    - Terminates the parameter list.

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ALL RIGHTS RESERVED.