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st: Re: Stata cannot do math?


From   "Joseph Coveney" <jcoveney@bigplanet.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: Stata cannot do math?
Date   Thu, 19 May 2011 09:19:35 +0900

Yu Xue wrote:

This may be a stupid question. Here are the command and Stata output:

.set obs 50
.gen a=100.1
.count if a==100.1
0
.tab a
100.1
.sum a
variable  obs  mean  s.d.  min    max
a            50    100.1  0    100.1  100.1
.gen b=a-100
.tab b
0.0999985

So, Stata shows that a is equal to 100.1, but actually, it is equal to
100.0999985....

Can anyone explain to me what this is? Do I have to set precision when
I do math in Stata? How to set precision?
Thanks!

--------------------------------------------------------------------------------

At Stata's command prompt, type:

findit precision

and then croll through the results to the half-dozen online FAQs and _Stata
Journal_ articles for some suggestions, in particular the use of the -float()-
function.

Yours not a stupid question, but it is a common one.  In general, when you have
basic questions like that, it's often a good idea (that is, it's quicker than
Stata List) to use -findit- or -search- at the command prompt to see whether
others have had the same problem.

Joseph Coveney


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