# Singularities in the Average Information Matrix

## !AISINGULARITIES

!AISINGULARITIES
forces ASReml to calculate Average Information (AI) updates
even though a singularity was detected in the AI matrix.
The AI matrix is used to
give updates to the variance parameter estimates.
In release 1, if singularities were present in the AI matrix,
a generalised inverse was used which effectively conditioned on
whichever parameters were identified as singular.
ASReml now aborts processing if such singularities appear
unless the
!AISINGULARITIES
qualifier is set.
Which particular parameter is singular is reported in the
variance component table printed in the
.asr
file.
The most common reason for singularities is that
the user has overspecified the model and is likely to misinterpret
the results if not fully aware of the situation.
Overspecification will occur in a direct product of two
unconstrained variance matrices,
when a random term is confounded
with a fixed term and when there is no information in the data
on a particular component. The best action
is to revise the variance model so that the ambiguity is removed,
or to fix one of the parameters in the variance model so that the model
can be fitted.
For instance, if !ASUV is specified,
you may also need !S2==1.
Only rarely will it be reasonable to specify
the
!AISINGULARITIES
qualifier.
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