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From: d89-mlt@sm.luth.se (Morgan Lindqvist)
Newsgroups: comp.sys.handhelds
Subject: HP48: User-defined derivative problemes
Message-ID: <1477@tau.sm.luth.se>
Date: 20 Feb 91 20:12:05 GMT
Distribution: comp
Organization: University of Lulea, Sweden
Lines: 27


Hello world!

We have some problems to define discrete Heaviside step function
U(t) and it's derivative Unit impulse SIGMA(t) in the same
directory, and after that use: 'dt(U(5*t))' EVAL.

We have defined U(t) like: \<< \-> t 'IFTE(t\>=0,1,0)' \>>
         and derU(t) like: \<< \-> t dt 'SIGMA(t)' \>>
        and SIGMA(t) like: \<< \-> t 'IFTE(t==0,1,0)' \>>

Now, if we try to derivative 'U(a*5)' the HP48 will say
following:
           der Error
           Undefined Local Name
           4:
           3:
           2:         'U(a*5)'
           1:              'a'

Can someone help us solving this problem.
================================================================
|Mattias Dahl                 &            Morgan Lindvqist    |
|d89-mdl@sm.luht.se                        d89-mlt@sm.luth.se  |
|                                                              |
|                 University of Lulea, SWEDEN                  |
================================================================