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From |
Nick Winter <nw53@cornell.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: St: Programming question, local macros |

Date |
Wed, 22 Sep 2004 09:59:40 -0400 |

This comes up periodically. You can get the same behavior this way:

. di -4^2

-16

What's happening is that Stata is evaluating your expression according to its order of operations: first the exponentiation, then the subtraction.

It does the same thing when you are using the macro: first substitutes the contents of the macro, so "`x'^2" becomes "-4^2" and then "-4^2" is evaluated as above.

Remember, Stata's doesn't look at the macro reference `x' and say "aha, here is a number," it just blindly substitutes the string -4 for `x' and goes on. (Of course, this is one of the reasons macros are so powerful.)

So in general you want to do something like:

local xsq = (`x')^2

. local x = -4

. local xsq = (`x')^2

. di `xsq'

16

--Nick Winter

At 08:37 AM 9/22/2004 -0500, you wrote:

--------------------------------------------------------Could someone please explain the following behavior? I'm running fully up to date Stata 8.2 on Windows 2000. In a program I have the following statements (with responses interspersed): . local x = -4 . display `x' -4 . local xsq=`x'^2 . disp `xsq' -16 I kind of expected xsq to have the value of 16 rather than -16. Thanks in advance. -- Dale Plummer Department of Biostatistics Vanderbilt School of Medicine S-2323 Medical Center North Nashville, Tennessee 37232-2158 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

Nicholas Winter 607.255.8819 t

Assistant Professor 607.255.4530 f

Department of Government nw53@cornell.edu e

308 White Hall falcon.arts.cornell.edu/nw53 w

Cornell University

Ithaca, NY 14853-4601

*

* For searches and help try:

* http://www.stata.com/support/faqs/res/findit.html

* http://www.stata.com/support/statalist/faq

* http://www.ats.ucla.edu/stat/stata/

**References**:**st: St: Programming question, local macros***From:*"Plummer, Dale" <dale.plummer@vanderbilt.edu>

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