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From |
"D H" <dave1063@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Tip: Exponentiated macros should be placed in parentheses. |

Date |
Mon, 11 Feb 2008 12:48:38 -0800 |

Stata contains a trap for novice programmers and users of certain commands such as nl. If a local or global macro contains a value that is less than zero, care should be taken when using the exponentiation operator. Example: . global A = -5 . display $A^2 -25 Woops. Apparently, exponentiation precedes negation. Since a macro is basically just text, Stata takes 5, squares it, then applies the negative sign. To do this properly, use parentheses: . display ($A)^2 25 That's better. Or, consider using a scalar: . scalar B = -4 . display B^2 16 For reference, here is Stata's order of evaluation for all operators, from first to last: ! (or ~),^,- (negation),/,*,-(subtraction),+,!=(or ~=),>,<,<=.>=,==,& and |. This trap (feature?) may very well be documented, though I couldn't find it with Google. I may be missing something. I am running version 8.2. * * 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/

**Follow-Ups**:**Re: st: Tip: Exponentiated macros should be placed in parentheses.***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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