[R] cdf

Duncan Murdoch murdoch at stats.uwo.ca
Wed Oct 14 00:53:05 CEST 2009


On 13/10/2009 6:43 PM, David Winsemius wrote:
> On Oct 13, 2009, at 5:12 PM, maram salem wrote:
> 
>> Dear all,
>> I have the cdf of the following power fuction distribution:
>> F(y)=(y/350)^a               ,0<y<350,
>> where " a " is some parameter with range a>0.
>> I want to use it as the argument of the discretize function of the  
>> actuar package.
>>
>> So I think I need to define this function to R so that if I entered  
>> a=1, I get the following
>> F(y)=(y/350)
>> and if I entered a=4.5, I get the following
>> F(y) =(y/350)^4.5
>> ........... and so on
>>
>> I've tried
>> a<-vector(mode="numeric",length=1)
>> powercdf<-function(a,y)
>> (y/350)^a
>>
>> But when I typed: powercdf(10,y)
>> instead of getting : (y/350)^10     (which is what I want)
>> I got : object y not found ??
>>
>> I want y to remain as it is, a continous variable, not for example  
>> seq(0,350).
>> Thank you in advance.
> 
> If you want symbolic algebra then use a system designed for such. If  
> you invoke a function in R you need to give it arguments for  
> evaluation  ... to numerical values.
> 
> If you want a function that returns a function, that is also possible.
> 
>  > cdffn <- function(y, arg) return( function(y) {y^arg} )

But don't do it like that.  If you do, you'll see things like this:

 > power <- 10
 > cdf10 <- cdffn(arg=power)  # don't need y as an argument.
 > power <- 1
 > cdf10(1:10)
  [1]  1  2  3  4  5  6  7  8  9 10

See my other post for a correct implementation using force().

Duncan Murdoch

>  > cdf10 <- cdffn(y, 10)
>  > cdf10(1:10)
>   [1]           1        1024       59049     1048576     9765625     
> 60466176   282475249  1073741824
>   [9]  3486784401 10000000000
> 
> 
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
> 
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