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From: billw@hpcvra.cv.hp.com. (William C Wickes)
Newsgroups: comp.sys.handhelds
Subject: Re: Derivatives with Units
Message-ID: <25590088@hpcvra.cv.hp.com.>
Date: 14 Jan 91 19:08:27 GMT
References: <76FB00858000005B@gacvx1.gac.edu>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 14

In general, you can avoid this kind of problem by keeping your variables
formal (i.e. undefined) until after the algebra is done, then substituting
values in at the end.  For your particular example with differentiation
involving units, the following procedure will work:

'X' RCL 'T' RCL \-> x t
\<< { X T } PURGE 'X/T' X \.d
    x 'X' STO t 'T' STO EVAL
\>>

Of course, this can be generalized to arbitrary calculations.

Bill Wickes
HP Corvallis