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7 Command file: Specifying variance structures 120G structure header and definition linesThere are g sets of G structure definition lines and each set is of the formmodel term dorder [key model [initial values][additional initial values]]order [key model [initial values][additional initial values]][qualifier][qualifier].order [key model [initial values] [qualifier][additional initial values]]• model term is the term from the linearmodel to which the variance structure applies;the variance structure may cover additionalterms in the linear model, see Section7.8NIN Alliance Trial 1989variety !Aid.row 22column 11nin89aug.asd !skip 1yield ∼ mu variety !r repl,!f mv1 2 122 row AR1 0.311 column AR1 0.3repl 1repl 0 IDV 0.1• d is the number of variance models and hence direct product matrices involvedin the G structure; the following lines define the d variance models,• order is either the number of levels in the term or the name of a factor thathas the same number of levels as the component,• key is usually zero but for power models (EXP, GAU,. . . ) provides the distancedata needed to construct the model,• model is the ASReml variance model identifier/acronym selected for the term,– variance models are listed in Table 7.3,– these models have associated variance parameters,• initial values are initial or starting values for the variance parameters, thevalues for initial values are as described above for R structure definition lines,• qualifier tells ASReml to modify the variance model in some way; the qualifiersare described in Table 7.4.7.5 Variance model descriptionTable 7.3 presents the full range of variance models, that is, correlation, homogeneousvariance and heterogeneous variance models available in ASReml. Thetable contains the model identifier, a brief description, its algebraic form and thenumber of parameters. The first section defines (BASE) correlation models and