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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Local in -if expressions |

Date |
Tue, 18 Mar 2008 20:02:10 -0000 |

The problem here is not to do with -if- or -in- as such. It is a matter of handling string comparisons. As an example, let us suppose that the program branched to local cons constant local tr notrend and you then try if (`cons'=="noconstant") & (`tr'="notrend") { A key rule here is: substitute macro names by their contents. So Stata sees if (constant =="noconstant") & (notrend ="notrend") { That first comparison makes sense if you have a variable called -constant- (or for that matter a string scalar with the same name). But you evidently don't; so Stata complains and throws you out. What you want is to compare a string with a string, so the code should be if ("`cons'"=="noconstant") & ("`tr'"="notrend") { In fact there is an extra bug in this line: it just has not bitten you yet. You need == twice, not once. if ("`cons'"=="noconstant") & ("`tr'"=="notrend") { I like to put spaces around most binary operators, but that's purely a matter of taste, apart from any discussion of readability. if ("`cons'" == "noconstant") & ("`tr'" == "notrend") { There may be other problems: I just focused on what should be generating the error message. Nick n.j.cox@durham.ac.uk Paulo Regis I am having a problem with local macros. Whenever I need to use the -if command, I cannot include in the expression the local. This is not the first time I had this kind od problem but I did not find a way aroud this time. For example, I have 5 dependent (y1-y5) and independent (x1-x5) variables, a trend (created by the code, and included as a variable named "trend") and I want to check for cointegration of each dependent on each independent variable, considering 3 alternative specifications 1_ No constant, No trend 2_ constant, No trend 3_ constant, trend The programme (which I include at the end of the email) selects the specification with the highest Zobs (this is a simplification, actually, i base the selection on AIC). At the end of the programme, I need to post the Zobs (i.e. sample statistic) together with the Zcrit (i.e. critical value). The critical values are from Mackinnon (1990), testing for cointegration. My problem is at the end of the code. I get the error: constant not found r(111); The three -if with locals in the expression, which I reproduce : if (`cons'=="noconstant") & (`tr'="notrend") { scalar Zcrit== -3.98 } if (`cons'=="constant") & (`tr'="notrend") { scalar Zcrit== -3.86 } if (`cons'=="constant") & (`tr'="trend") { scalar Zcrit== -3.39 } What am I doing wrong? (Please, take in mind my code is much more complicated and I cannot check the Zobs and Zcrit by hand. Also, the if blocks include other commands to perform some complementary checks) Cheers Paulo Regis * COMPLETE PROGRAMME: capture postclose Posting capture drop trend capture drop r postfile Posting DepVar IndepVar Zobs Zcritcons Constant trend using "C:\LongRun_VEC.dta", replace global DepVar "y1 y2 y3 y4 y5" global Var "X1 X2 X3 X4 X5" gen trend=_n tsset trend foreach x of global Var { foreach y of global DepVar { regress `y' `x' predict r, residuals *No Constant and No Trend dfuller r, noconstant scalar Zobs=r(Zt) local cons noconstant local tr notrend *Constant and No Trend dfuller r, scalar Zobs2=r(Zt) if Zobs2<Zobs2{ scalar Zobs=Zobs2 local cons constant local tr notrend } *Constant and Trend dfuller r, trend scalar Zobs2=r(Zt) if Zobs2<Zobs{ scalar Zobs=Zobs2 local cons constant local tr trend } dfuller r, `cons' `tr' if (`cons'=="noconstant") & (`tr'="notrend") { scalar Zcrit== -3.89 } if (`cons'=="constant") & (`tr'="notrend") { scalar Zcrit== -3.86 } if (`cons'=="constant") & (`tr'="trend") { scalar Zcrit== -3.39 } drop r post Posting (`y') (`x') (Zobs) (Zcrit) ("`cons'") ("`tr'") } * * 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: Local in -if expressions***From:*"Paulo Regis" <pauloregis.ar@googlemail.com>

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