st: Hansen J with constraints in Ivreg2

["Min Y. Tan" <mtan@learnlink.emory.edu>]

the problem is that i can't re-estimate the equation as my orginal looks like
this:

ivreg2 win (temp = one instru1 instru2), gmm ro cluster(year)

Initially i was estimating the coefficient on temp.
but now I want to be able estimate the J stat if i impose the coefficient on
temp to be 0.5

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