R help - Apr 2007 - convergence

hie..
how can i write a loop that makes algorithm keeps repeating until a solution
is converged?do i use a for loop? i know that we can use for loop to ask for
a number of repetitions, but how to use it to ask the algorithm to keep
repeating until a solution is converged?
Thanks
-- 
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No, use a while loop. Something like

change <- 1
while(abs(change) > .001 ){
	do stuff
	change <- updated change
}
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of rach.s
> Sent: Thursday, April 19, 2007 8:00 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] convergence
> 
> 
> hie..
> how can i write a loop that makes algorithm keeps repeating 
> until a solution is converged?do i use a for loop? i know 
> that we can use for loop to ask for a number of repetitions, 
> but how to use it to ask the algorithm to keep repeating 
> until a solution is converged?
> Thanks
> --
> View this message in context: 
> http://www.nabble.com/convergence-tf3606834.html#a10076822
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
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> PLEASE do read the posting guide 
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> and provide commented, minimal, self-contained, reproducible code.
>

Hi,
> how can i write a loop that makes algorithm keeps repeating until a
solution
> is converged?do i use a for loop? i know that we can use for loop to ask
for
> a number of repetitions, but how to use it to ask the algorithm to keep
> repeating until a solution is converged?
I don't know what your problem is, and I am far from being a specialist, but
it
seems to me that in this case you often use a variable, for example
'epsilon',
which measures your "level of convergence". Then you could you use a
loop which
repeats while this measure is above a certain threshold, for example :

while (epsilon > 0.0001) {
   ... repeated expressions ...
}


Hope that helps,

-- 
Julien

On 19-Apr-07 12:00:17, rach.s wrote:
> 
> hie..
> how can i write a loop that makes algorithm keeps repeating
> until a solution is converged?do i use a for loop? i know
> that we can use for loop to ask for a number of repetitions,
> but how to use it to ask the algorithm to keep repeating
> until a solution is converged?
> Thanks
There are various ways round this, but a 'for' loop with
a fixed number of iterations is not usully one of them!

The simplest is to use while(). A possibly strategy is

  Y.old <- initial.Y
  while(TRUE){
    Y <- compute.Y(Y.old, ...)
    if(abs(Y - Y.old) < small.number) break
    Y.old <- Y
  }

This will loop indefinitely until the convergence criterion

  abs(Y - Y.old) < small.number

is met, and then stop.

Best wishes,
Ted.

--------------------------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 19-Apr-07                                       Time: 14:01:51
------------------------------ XFMail ------------------------------

rach.s wrote:
> hie..
> how can i write a loop that makes algorithm keeps repeating until a
solution
> is converged?do i use a for loop? i know that we can use for loop to ask
for
> a number of repetitions, but how to use it to ask the algorithm to keep
> repeating until a solution is converged?
gregory.liebniz<-function(tol=0.0001) {
  pi.diff<-1
  iter<-0
  numer<-1
  last.pi<-0
  pi4<-0
  while(pi.diff > tol) {
   pi4<-pi4+numer/(2*iter+1)
   this.pi<-pi4*4
   pi.diff<-abs(this.pi-last.pi)
   last.pi<-this.pi
   iter<-iter+1
   numer<- -numer
  }
  return(this.pi)
}

What you want is probably a while loop, testing for a level of 
convergence like this simple method for calculating pi.

Jim