title: Sommer mapping mmer2 function to mmer
body: <p>I have a matrix with the following columns: 2 fixed effects, a dependent variable and 2 IDs which match the rows and columns of my variance/covariance matrix (GRM1 and GRM2). With the previous version of sommer I used the mmer2 function</p>
  
  <p>mmer2_result &lt;- mmer2(y ~ fixed_effect1 + fixed_effect2, random=~g(id1)+g(id2),G=list(id1=GRM1, id2=GRM2),rcov=~units, silent=TRUE, data=data,constraint=FALSE)</p>
  
  <p>How would I map this over to the mmer function in the updated package? </p>