命令：
program MyOLS3
args lfn beta sigma
quietly {
replace ‘lfn’ = ln(normalden($ML_y1, ‘beta’, ‘sigma’))
}
end
ml model lf MyOLS3 (y = eduyear1 experi experi2  nonruralspeci marriage health     middle   west) /sigma, tech(nr 5  bfgs 5 dfp 5  bhhh 5)
ml check
ml  search
ml max
                                从ml  check 开始，出现问题：

Test 1:  Calling MyOLS3 to check if it computes log likelihood and
         does not alter coefficient vector...
       opt__eval_cycle():  3301  subscript invalid
             opt__eval():     -  function returned error
    _optimize_evaluate():     -  function returned error
       _mopt__evaluate():     -  function returned error
     mopt__check_test1():     -  function returned error
      _moptimize_check():     -  function returned error
            Mopt_check():     -  function returned error
                 <istmt>:     -  function returned error
r(3301);