gmmWald — Wald test
rwd = gmmWald(rgmm,R,r,np)
rgmm = tlist result for unrestricted estimation
R = is the (s x #parameters) R matrix of linear constraints in Rb = r
r = (s x 1) r vector in Rb = r
np = 'noprint' if the user does not want to print the results
rwd a tlist which arguments can be:
-rwd('chistat') = test statisitc
-rwd('pvalue') = pvalue of the test
-rwd('df') = number restriction