Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!hp48sx
From: hp48sx@wuarchive.wustl.edu (HP48SX Archive Maintainer)
Newsgroups: comp.sys.handhelds
Subject: A strange feature (a bug?)
Keywords: symbolic integration/differentation in DEG mode
Message-ID: <1990Oct10.093506.8848@wuarchive.wustl.edu>
Date: 10 Oct 90 09:35:06 GMT
Organization: Washington University in Saint Louis, MO
Lines: 28

There are some problems using differentation/integration when in degrees
mode on the hp48sx. The manual says in many places that you should make
sure to switch to RADians mode if appropriate, but If I end up putting
degrees in the formulae then there is no reason why I should use radians
when calculating the derived function.

If I try to evaluate dX(sin(X)) then I get:
cos(x)*(dX(X)*(pi/180))
/* if the factor pi/180 should be applied, then it should be multiplied
   to the x in cox(x), but even this is not correct */
further EVAL gives:
cos(X)*(pi/180)

And we all know that cos(60) is 1/2  (the 60 is in degrees), and this is
the correct result. But we still get the factor (pi/180) which will give
me a wrong result.

As it looks like the hp48 is only capable of giving the correct results
in radians mode, the HP should have ensured that
integration/differentation is always carried out in radians mode, and
then switch back to the previous mode when done.

Povl

-- 
*******************************************************
Povl H. Pedersen             hp48sx@wuarchive.wustl.edu
HP48sx archive maintainer