[R] Finding a scalar value...

[Adaikalavan Ramasamy]

Your best option is to read the relevant help files.

A simple (untested) example to find R when P, T and scal.fn=Z is given, 
is to do this:

  my.fun <- function(P, R, T, Z) scal.fn(P, R, T) - Z
  uniroot( fn, R=rr, T=tt, Z=zz, lower=-1000000, upper=1000000 )$root

You have to make an intelligent guess on the upper and lower ranges for 
the parameter R. I have used +/- 1 million as a silly example.

HOWEVER, I do not think this works when P,R,T,Z are scalars. Try it to 
be sure. If not, then you may have to write a for or apply loop.

Regards, Adai




On 16/08/2010 13:19, Petar Milin wrote:
> Thanks for the answer!
> However, if I would have scal.fn() like below, how would I apply
> uniroot() or optimize() or the like?
>
> Best,
> PM
>
> On 16/08/10 13:24, Adaikalavan Ramasamy wrote:
>> You probably need to look up on how to write functions.
>>
>> Try
>>
>>   scal.fn<- function(P, R, T){
>>    out<- ( 1/R - T ) / ( P - T )
>>    return(out)
>>   }
>>
>> Here is a fake example:
>>
>>   df<- cbind.data.frame( P=rnorm(10), R=rnorm(10), T=rnorm(10) )
>>   scal.fn( df$P, df$R, df$T )
>>
>> Or are you trying to solve other parameters given scal values? If so,
>> try having a look at functions like uniroot().
>>
>> Regards, Adai
>>
>>
>> On 16/08/2010 11:48, Petar Milin wrote:
>>> Hello!
>>> I need to find a simple scalar value:
>>> Scal = ((1/R) - T) / (P - T),
>>> where R, T, and P are vectors in a data.frame.
>>>
>>> Please, can anyone tell me how to solve that in R?
>>>
>>> Best,
>>> PM
>>>
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>>
>>