[R] Solving Equations

[Duncan Murdoch]

On 12-01-22 3:56 PM, R. Michael Weylandt wrote:
> CRAN suggests it's not available for windows since the build can't be
> automated: http://cran.r-project.org/bin/windows/contrib/r-release/ReadMe
>
> but it suggests builds are available from Prof Ripley (to whom be
> honor and praise for ever and ever, amen!) here:
> http://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/2.14/

That build would normally be found automatically by

install.packages("XML")

and it was when I just tried it.  Perhaps David has "CRAN (extras)" 
disabled in his list of selected repositories?

Duncan Murdoch

>
> Michael
>
> On Sun, Jan 22, 2012 at 3:52 PM, David Stevens<david.stevens at usu.edu>  wrote:
>> I'm following this thread and got curious about Ryacas. After installing
>> yacas and Ryacas, I was alerted to the missing XML package for Windows.
>> I couldn't find in on a couple of mirrors so I tried
>> http://www.omegahat.org/RSXML/ and
>>
>> install.packages("XML", repos = "http://www.omegahat.org/R")
>>
>> but got
>>
>> Installing package(s) into 'D:/Users/David Stevens/Documents/R/win-library/2.14'
>> (as 'lib' is unspecified)
>> Warning message:
>> In getDependencies(pkgs, dependencies, available, lib) :
>>    package 'XML' is not available (for R version 2.14.1)
>>
>> for my troubles. The date on the omegahat site is 17 Jan 2012. Am I missing something?
>>
>> David Stevens
>>
>>
>>
>> On 1/22/2012 12:39 PM, Gabor Grothendieck wrote:
>>> On Sun, Jan 22, 2012 at 1:25 PM, Eliano<eliano.m.marques at gmail.com>    wrote:
>>>> People,
>>>>
>>>> I'm researching some Bayesian statistic topics and in the midle of my study
>>>> i found a very simple problem and i'm trying to find a simple package to
>>>> solve this type of equations:
>>>>
>>>> Lets say that i need to compute beta values for the beta distribution and i
>>>> now for example:
>>>>
>>>> E(teta)=a/(a+b) = 0,5
>>>> Var(teta)=ab/((a+b)^2(a+b+1))=0.05
>>>>
>>>> So if i want to solve this to non-linear system to find a,b for the beta
>>>> distribution wich pack should i use?
>>>>
>>> The equations giving a and b as a function of m and v are:
>>>
>>>> library(Ryacas)
>>>> a<- Sym("a"); b<- Sym("b")
>>>> m<- Sym("m"); v<- Sym("v")
>>>> Solve( List(a/(a+b) == m, a*b/((a+b)^2*(a+b+1)) == v), List(a, b) )
>>> expression(list(list(a == m^2 * (1 - m)/v - m, b == a/m - a)))
>>>
>>> Based on the above we write this R function:
>>>
>>> beta.parms<- function(m, v) {
>>>      a<- m^2 * (1-m)/v - m
>>>      b<- a/m - a
>>>      c(a = a, b = b)
>>> }
>>>
>>> and run it:
>>>
>>>> beta.parms(m = 0.5, v = 0.05)
>>> a b
>>> 2 2
>>>
>>
>> --
>> David K Stevens, P.E., Ph.D., Professor
>> Civil and Environmental Engineering
>> Utah Water Research Laboratory
>> 8200 Old Main Hill
>> Logan, UT  84322-8200
>> 435 797 3229 - voice
>> 435 797 1363 - fax
>> david.stevens at usu.edu
>>
>>
>>
>>
>>         [[alternative HTML version deleted]]
>>
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>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.