6/29/2020
The primary way to add new functions to Ferret is by means of an
internally-linked external function. Though less flexible than
native functions - the user needs to specificially subset the data
they're sending into the function -- the writing of them is simpler.
How to write External functions is documented in the Documentation at
https://ferret.pmel.noaa.gov/Ferret/documentation/external-functions


8/5/92 *sh*
This is a summary of the routines that need to be changed to add a new 
function (like RHO_IES) to FERRET

xalgebra_data - add name and number of args

operate.f - add new functions to type declarations
	  - add execution code at 3800 - 4300




WRITE:  "do_smth_..." patterned after do_smth_binml.f
	
ferret.parm:	     add trans_smth_...

interp_stack.parm:   isact_smth_...

xalgebra_data.f:     add alg_trans_...text/title/num/etc

get_context_mode:    error message text, only (could be automated ...)

interp_stack:	     add EXTERNAL DO_SMTH_...
		     add IF ( isact...   )  CALL ...

offset_ss.f:	     add DATA and check out where this transformation belongs
		     in the program logic

