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Re: st: Re: Memory


From   "Austin Nichols" <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Re: Memory
Date   Thu, 13 Nov 2008 10:09:27 -0500

Victor M. Zammit:
I also don't understand the point of this exercise--but you should
read -help simul- and try e.g.

prog makez, rclass
 syntax [, obs(integer 31)]
 clear
 set obs `obs'
 gen a = invnorm(uniform())
 ttest a=0
 return scalar t=r(t)
end
simul, reps(100000) seed(123): makez


On Thu, Nov 13, 2008 at 9:56 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> I still don't understand what you are trying to do. But I can comment on
> your code.
>
> You are looping round 40,000 times and writing a single result to 40,000
> data files. Then you are looping round to put all those 40,000 data
> files in one.
>
> I'd do that directly this way using just one extra file:
>
> clear
> set obs 31
> gen a = .
> tempname out
> postfile `out' t using myresults.dta
> qui forval i = 1/40000 {
>        replace a = invnorm(uniform())
>        ttest a = 0
>        post `out' (r(t))
> }
> postclose `out'
>
> I still doubt 40,000 is anywhere big enough to get an answer.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Victor M. Zammit
>
> * a} The data that I have is from generating random samples of whatever
> size,in this case of size 31,from a normally distributed,infinitely
> large,
> population; ie
>
> local i = 1
>
> while `i'<= 40000 {
>
> drop _all
>
> set obs 31
>
> gen a = invnorm(uniform())
>
> qui ttest a = 0
>
> replace a = r(t) in 1
>
> keep in 1
>
> save a`i',replace
>
> local i = `i'+1
>
> }
>
> * I use 40000 due to memory constraint.Appending the a[i]'s together
> gives
> me a variable of 40000 observations ,ie
>
> use a1,clear
>
> local i = 2
>
> while `i'<= 40000 {
>
> append using a`i'.dta
>
> local i = `i'+1
>
> }
>
> save ais40000,replace
>
> * b) From ais40000.dta I get the density <= 1.31, presumably to get the
> density of 90% , <= 1.697 to get the density of 95% etc etc,according to
> the
> official ttable, ie
>
> capture program drop density
>
> program define density
>
> use ais40000,clear
>
> count if a<= `1'
>
> di " density >=" "`1'" " = " r(N)/40000
>
> end
>
> density 1.31
>
> density 1.697
>
> density 2.042
>
> density 2.457
>
> density 2.75
>
> * For smaller degrees of freedom,the discrepancy is much higher.I would
> like
> to know how if it is at all possible to resolve memory constraint .
>
>
> *
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