ASReml-S reference manual - VSN International

4.7 Constraining variance parameters 522. extract the variance component names as the dimnames attribute of M.an exampleA default data frame gammas.table to work with is generated by setting the start.valuesargument to asreml. This data frame contains a factor, Gammas, the levels of which arethe names of the variance parameters. Other factors or variates created in this data frameand named in the formula argument to asreml.constraints() are used to generate M.By way of example, consider a model containing a first order interaction term (A:B, say)where the outer factor (A) is of order 7 and we wish to model it with an unstructuredvariance matrix with some parameters constrained. Suppose the required pattern of constraintsamong the variance parameters is:v 11v 21 v 22v 31 v 32 v 33v 31 v 32 0 v 33v 31 v 32 0 0 v 33v 31 v 32 0 0 0 v 33v 31 v 32 0 0 0 0 v 33That is, there are only 7 distinct parameters from the original 28 and one of these is tobe fixed at zero. Furthermore, suppose that none of the remaining variance parametersfrom other terms in the model are to be subject to any constraints.The following call> model.gam