Re: [R] D(dnorm...)?

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Thu 26 Jan 2006 - 10:43:35 EST

Hi, Prof. Ripley:

          Thanks for the explanation. If I had read your book more carefully, I would not have needed this email exchange.

	  Thanks again,
	  Spencer Graves

Prof Brian Ripley wrote:

> On Wed, 25 Jan 2006, Spencer Graves wrote:
>

>> Hi, Bert:
>>
>>       I think I was too terse:  Why didn't I get an error message?  
>> When I
>> tried the same thing with "dpois", I got an error message:
>>
>> > D(expression(dpois(x, prob)), "mean")
>> Error in D(expression(dpois(x, prob)), "mean") :
>>     Function 'dpois' is not in the derivatives table
>>
>>       With "dnorm", I got "0"!.  Whe didn't I get an error message?

>
>
> Because dnorm _is_ in the derivatives table, as a function of x. (So is
> pnorm.) These are functions we write as \phi and \Phi in Statistics 101.
>
> This is not particularly well documented in R, but it is in MASS4 pp.
> 437-8.
>
> It would be worth enhancing the help page with the list of known
> functions. Long ago we talked about making it extensible, but nothing
> happened.
>
>
>>
>>       Thanks for the reply.
>>       Spencer Graves
>>
>> Berton Gunter wrote:
>>
>>> dnorm() is an internal function, so I don't see how D (or deriv) can do
>>> anything with it symbolically. Am I missing something?
>>>
>>> -- Bert
>>>
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: r-help-bounces@stat.math.ethz.ch
>>>> [mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Spencer Graves
>>>> Sent: Wednesday, January 25, 2006 2:43 PM
>>>> To: r-help@stat.math.ethz.ch
>>>> Subject: [R] D(dnorm...)?
>>>>
>>>>       Can someone help me understand the following:
>>>>
>>>>> D(expression(dnorm(x, mean)), "mean")
>>>>
>>>> [1] 0
>>>>
>>>>> sessionInfo()
>>>>
>>>>
>>>> R version 2.2.1, 2005-12-20, i386-pc-mingw32
>>>>
>>>> attached base packages:
>>>> [1] "methods"   "stats"     "graphics"  "grDevices" "utils"
>>>>  "datasets"
>>>> [7] "base"
>>>>
>>>>       By my computations, this should be something like
>>>> ((mean-x)/sd^2)*dnorm(...).
>>>>
>>>>       Thanks for your help.
>>>>       Spencer Graves
>>>>
>>>> ______________________________________________
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>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide!
>>>> http://www.R-project.org/posting-guide.html
>>>>
>>>
>>>
>>
>> ______________________________________________
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>

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Jan 26 10:49:08 2006

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