From lylek@utk.edu  Thu Aug 22 13:45:47 2002
From: lylek@utk.edu (lylek@utk.edu)
Date: Thu, 22 Aug 2002 14:45:47 +0200 (MET DST)
Subject: Symbolic differentiation ("D","deriv", etc.) (PR#1928)
Message-ID: <200208221245.OAA14923@pubhealth.ku.dk>

Full_Name: Lyle W. Konigsberg
Version: 1.5.1
OS: Windows
Submission from: (NULL) (160.36.64.99)


I apparently found an error in how "deriv" puts a derivative to the screen
(though the internal representation is correct).  Here's what I was doing for a
class example:

> lnlk<-expression(15*log(p)+11*log(1-p))
> p<-15/26
> D(D(lnlk,"p"),"p")
-15 * (1/p^2) + 11 * (1/(1 - p)^2)
> eval(D(D(lnlk,"p"),"p"))
[1] -106.5212
> -15 * (1/p^2) + 11 * (1/(1 - p)^2)
[1] 16.38788

>From S+ I have the following:

> lnlk<-expression(15*log(p)+11*log(1-p))
> p<-15/26
> D(D(lnlk,"p"),"p")
 - (15 * 1/p^2 + 11 * 1/(1 - p)^2)
> - (15 * 1/p^2 + 11 * 1/(1 - p)^2)
[1] -106.5212

R seems to be dropping the outer parentheses.


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Symbolic differentiation ("D","deriv", etc.) (PR#1928)
lylek@utk.edu