[R] Solving Equations

[R. Michael Weylandt]

I would have assumed it was just an artifact of the fact Prof Stevens
specified the omegahat repos in his call, though I haven't looked at
the innards of install.packages to see when/how the re-route to CRAN
extras happens.

Michael

On Sun, Jan 22, 2012 at 4:08 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> 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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>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>> ______________________________________________
>> 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.
>
>