# Extended Factor Analytic model

## xfa() function

xfa(`f,k`)

Factor
analytic models are available in
three forms in ASReml: FA`k`,
FACV`k`
and XFA`k`
where `k` is the number of factors.
The XFA`k` form is
a sparse formulation that requires an extra `k` levels to be
inserted into the mixed model equations for the `k`
factors. This is achieved by the xfa(`f,k`) model function
which defines a design matrix based on the design matrix for `f`
augmented with ` k` columns of
zeros for the ` k` factors.
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