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"[email protected]" <[email protected]> |

Subject |
st: MLE method Could not find feasible values |

Date |
Sun, 22 Dec 2013 10:22:34 +0800 |

I am currently trying to program my own patent value elimination models using Statas ml command, and I have got a original code that one author had used for the same question. And my model is a bit different with his one. So I have to make some adapt. So far, my attempts have not been very successful. I have checked the help files of Stata, Statalist and gone through the book of William Gould et al. on programming maximum likelihood in Stata (they have some advice on ml check but I cannot fix the problem) and have asked people at my department to no avail, and I have discussed the model with teachers and they said the model setting is ok. Since I am really a rookie in programming mle problem using stata, any advice will be useful. My do file is shown below: *estimate the parameter with mle set more off capture program drop myprog_patent program define myprog_patent version 12.0 args lnf mu sigma d *d stands for the depreciation rate tempvar lnzt lnzt1 * termiyear means the expired year of the patent quietly gen double `lnzt'=ln(ct)-ln(1-exp(-(`d'+0.1)))-(`d'*$ML_y1)-ln(`d'+0.1) quietly gen double `lnzt1'=ln(ct1)-ln(1-exp(-(`d'+0.1)))-(`d'*(($ML_y1)-1))-ln(`d'+0.1) * this means that the patent is expired but not renewed full term quietly replace `lnf' = ln(normal((`lnzt'-`mu')/`sigma')) if termiyear!=. & $ML_y1==0 quietly replace `lnf' =ln(normal((`lnzt'-`mu')/`sigma')-normal((`lnzt1'-`mu')/`sigma')) if termiyear!=. & t2==1 * this means that the patent is expired and renewed full term quietly replace `lnf' = ln(normal(-(`lnzt'-`mu')/`sigma')) if appliyear<1994 & $ML_y1==15 * this means that the patent is not expired quietly replace `lnf' = ln(normal(-(`lnzt'-`mu')/`sigma')) if termiyear==. end * t stands for termiyear - applyear if the patent is expired or 2011 - applyear if the patent is still renewed ml model lf myprog_patent (mu: t = ) /sigma /d ml check ml init mu=10.3948 sigma=4.3920 dep=0.2601 ml search ml maximize end Here is the results of the do file: . ml model lf myprog_patent (mu: t = ) /sigma /d. ml check Test 1: Calling myprog_patent to check if it computes log likelihood and does not alter coefficient vector... Passed. Test 2: Calling myprog_patent again to check if the same log likelihood value is returned... Passed. The initial values are not feasible. This may be because the initial values have been chosen poorly or because there is an error in myprog_patent and it always returns missing no matter what the parameter values. Stata is going to search for a feasible set of initial values. If myprog_patent is broken, this will not work and you will have to press Break to stop the search. Searching initial: log likelihood = -<inf> (could not be evaluated) searching for feasible values could not find feasible values r(491); end of do-file r(491); Could you give me some advice on how to fix this problem, does this mean I have something wrong with my data set, or it is my function setting which is wrong, or some other things that I just haven't come up with. Many regards. Jason Lee * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

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