Random submodel

Random terms in the model

The !r random terms in the model formula
  • comprise random covariates, factors and interactions including special functions and reserved words,
  • involve an initial non-zero variance component or ratio (relative to the residual variance) default 0.1; the initial value can be specified after the model term or
  • if the variance structure is not scaled identity, it must be defined using a G structure definition.
  • an initial value of its variance (ratio) may be followed by a !GP (keep positive, the default), !GU (unrestricted) or !GF (fixed) qualifier,
  • use !{ and !} to group model terms that may not be reordered. Normally ASReml will reorder the model terms in the sparse equations - putting smaller terms first to speed up calculations. However, the order must be preserved if the user defines a structure for a term which also covers the following term(s) (a way of defining a covariance structure across model terms). Grouping is specifically required if the model terms are of differing sizes (number of effects). For example, for traits weaning_weight and yearling_weight, an animal model with maternal weaning weight should specify model terms
    !{ Trait.animal at(Trait,1).dam !}
    when fitting a genetic covariance between the direct and maternal effects.
     wwt ~ mu Year age !r sire 0.15 !GP

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