# 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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