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From: RJW0180@TNTECH.BITNET
Newsgroups: comp.sys.handhelds
Subject: RE: hp48: User-defined derivative problems
Message-ID: <480201B640004A1A@TNTECH.BITNET>
Date: 25 Feb 91 22:41:00 GMT
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To: handhelds@gacvx1.gac.edu
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> 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)' \>>
>                       ...
 
Maybe you're talking about a different Unit impulse function, but the one
I'm familiar with (what my Signals book and Probability and Random Variables
book call delta(t)) is defined as a "function" having the following
properties...
 
delta(t) = 0, t<>0
and the integral of delta(t) with respect to t over all time equals 1.
 
delta(0) approaches infinity, not 1. The integral of it from 0- to 0+ (or a
y interval containing 0) does equal 1.
 
If you're talking about something else, sorry, but I just though I'd point
that out.
 
-Randy Weems
RJW0180@TNECH.BITNET