SIOSEIS PROCESSING FLOW

SIOSEIS processes seismic data in the order the user describes on the 
PROCS statement.  After each trace is entered into the system, it is 
processed in order as far as it can before another trace is entered.  
This makes SIOSEIS into a 'trace processor'.  There are 2 major
advantages of a trace processor over a 'shot processor'.  First, each
trace is left in memory as long as possible, thus minimizing I/O time
to disk.  Secondly, there are no limits as to the number of traces in
a shot or gather.

Some seismic processes require more than 1 trace before they are finished,
such as stack.  This type of process is called a 'multi-input' process.
Processing control (or order) can not be advanced until enough traces are
entered into the system to satisfy the multi-input process requirements.
Processing order is retraced (backed-up) until an input process is found,
and then the processing order goes in a forward direction again.

Some seismic processes may output more than one trace from a single input
trace, such as constant velocity gathers.  This type of process is called
a multi-output process.  In this case, processing proceeds after the
multi-output process until a trace is eliminated, then the processing 
order backs up until it gets to the multi-output process, which then
inputs the next trace if one is available.

SIOSEIS has a table that defines each process as an input process, or an
output process, or neither.  Each process sets the number of traces to be
passed to the next process.  If the number of traces to be passed is zero,
then SIOSEIS searches the user defined processing list backwards from 
that process until an input process is found.  Processes input, syn, 
stack, and gather are input processes.

Example 1:
     procs input filter output end
trace 1 is input, then filtered, then output, then trace 2 is input, etc.

Example 2:
     procs input stack filter output exec end
the processing order will be input stack until all of an rp is finished,
then the stacked trace will be filtered and output.  The processing order
then goes back to input.