R help - Feb 2008 - Error in optim while using fitdistr() function for estimation of parameters

Hello,

I am trying to fit distribution for data consisting of 421 readings.It is
basically no of requests arrived per minute.It contains many 0 entries as no
of requests.When i use
fd<-fitdistr(V2,"gamma")
I get following error:
Error in optim(x = c(0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,  :
        initial value in 'vmmin' is not finite

What should I do ? I need this function because I want to get value of
estimated parameters.
Is there any other function to perform such calculations?
Please help me.
Thank You.

Code is as follows:
x<-data.frame()
N<-data.frame((read.table("cs2ip.txt")))
attach(N)
library(MASS)
fd<-fitdistr(V2,"gamma")

Aswad

	[[alternative HTML version deleted]]

Chenge your model, most likely.

You are telling us a) the response is discrete and b) there is a
substantial probability that the value is zero.  The gamma distributon
is a model for a continuous response, your response is integer valued.
Perhaps you should consider something the Poisson or Negative Binomial.

Evem from the little you give us, the problem seems more statistical
than computational to me. 


Bill Venables
CSIRO Laboratories
PO Box 120, Cleveland, 4163
AUSTRALIA
Office Phone (email preferred): +61 7 3826 7251
Fax (if absolutely necessary):  +61 7 3826 7304
Mobile:                         +61 4 8819 4402
Home Phone:                     +61 7 3286 7700
mailto:Bill.Venables at csiro.au
http://www.cmis.csiro.au/bill.venables/ 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Aswad Gurjar
Sent: Sunday, 10 February 2008 4:17 PM
To: r-help at r-project.org
Subject: [R] Error in optim while using fitdistr() function for
estimationof parameters

  Hello,

I am trying to fit distribution for data consisting of 421 readings.It
is
basically no of requests arrived per minute.It contains many 0 entries
as no
of requests.When i use
fd<-fitdistr(V2,"gamma")
I get following error:
Error in optim(x = c(0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
:
        initial value in 'vmmin' is not finite

What should I do ? I need this function because I want to get value of
estimated parameters.
Is there any other function to perform such calculations?
Please help me.
Thank You.

Code is as follows:
x<-data.frame()
N<-data.frame((read.table("cs2ip.txt")))
attach(N)
library(MASS)
fd<-fitdistr(V2,"gamma")

Aswad

	[[alternative HTML version deleted]]

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