How to do a EM for my mixture model

[Bing Zhang]

Dear statalist:
I want to do a mixture model of two ols whose coffients are constrained to be same.I have written a maximum likelihood estimation to this problem but it only worked when varaibles are limited.Althouth fmm released by stata can solve it,my research need to program by myself.I wonder if you can tell me how to do Expectation-Maximization algorithm for my model.
the code is as following:

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* Example generated by -dataex-. To install: ssc install dataex
webuse womenwk, clear


capture program drop fmmreg
program fmmreg
qui {
   args lnf xb1 lns1 xb2 lns2 lp 
   tempvar f1 f2
   gen double `f1'=normalden($ML_y1,`xb1',exp(`lns1'))
   gen double `f2'=normalden($ML_y1,`xb2',exp(`lns2'))
   tempvar p
   gen double `p'=exp(`lp')/(1+exp(`lp'))
   replace `lnf'=ln(`p'*`f1'+(1-`p')*`f2') 
}
end


constraint 1 [xb1]age=[xb2]age
constraint 2 [xb1]education=[xb2]education
constraint 3 [xb1]married=[xb2]married
constraint 4 [xb1]child=[xb2]child

ml model lf fmmreg (xb1:wage=age education married children ) (lns1:) (xb2:wage=age education married children ) (lns2:) (lp:),constraints(1/4)
ml max
end

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