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st: RE: St: Dataset generation


From   "Nick Winter" <nwinter@policystudies.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: St: Dataset generation
Date   Fri, 14 Jun 2002 11:36:04 -0400

I think you want:

	. clear
	. set obs 81
	. range x -2 2
	. expand 81

The "imprecision" you are seeing is a side-effect of storing decimal
numbers in binary.  There is a FAQ somewhere on that.

--Nick W

-----------------------------------------------------------
 Nicholas Winter, Ph.D.                     P 202.939.5343
 Policy Studies Associates                  F 202.939.5732
 1718 Connecticut Avenue, NW     nwinter@policystudies.com
 Washington, DC 20009-1148           www.policystudies.com
----------------------------------------------------------- 

> -----Original Message-----
> From: J.A.Fennema@hw.ac.uk [mailto:J.A.Fennema@hw.ac.uk] 
> Sent: Friday, June 14, 2002 11:32 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: St: Dataset generation
> 
> 
> Please could somebody explain to me how this could occur:
> 
> I want to generate a dataset with 6561 observations, with two 
> variables, let us say x and y, which take values between -2 and 2, 
> with step value 0.05. The aim of this is to test a function which I 
> have programmed which is causing some trouble. Therefore I need 81 
> occurences of x==-2, and 81 of x==-1.95 and so on for both x and y. 
> If I construct x as follows (crude so feel free to suggest 
> alternatives)
> 
> egen ind=fill (1 2)
> replace ind=ind-1
> gen x=int(ind/81)
> replace x=(x/20)-2
> 
> this should work, and does when the data is displayed to 2 decimal 
> places. However closer examination of the data with the data browser 
> shows some anomalies, where rather that x==-.95 it actually reads 
> x==.-9499999. This occurs for many values in between -1 and 1 and 
> attempts to rectify it using
> 
> gen x2=round(x,0.05)
> 
> have not bourne fruit. What am I missing?
> 
> Many thanks in advance,
> Julian
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