A sample of size n is drawn from each of two normal populations, both of which have variance

^{2}. The mean of the two populations are (a+b) and (a-b), respectively, where a,b>0. The sample observations are denoted x

_{ij, }i=1,2 and j=1,...,n. The question is " What are the maximum likelihood estimators of a,b,

^{2}?

Thanks in advance.