Variance Models

OWN variance model

The OWN variance structure is a facility whereby users may specify their own variance structure. This facility requires the user to supply a program MYOWNGDG that reads the current set of parameters, forms the G matrix and a full set of derivative matrices, and writes these to disk. Before each iteration, ASReml writes the OWN parameters to a file, runs MYOWNGDG (which it presumes forms the G and derivative matrix) and then reads the matrices back in. An example of MYOWNGDG.f90 is distributed with ASReml. It duplicates the AR1 and AR2 structures. The following job fits an AR2 structure using this program.
 Example of using the OWN structure
   variety 25
 barley.asd !skip 1 !OWN MYOWN.EXE
 yield ~  variety
 1 2
 10 0 AR1 .1
 15 0 OWN2 .2 .1 !TRR
The file written by ASReml has extension .own and looks like
    15    2    1
  This file was written by asreml for reading by your
  program MYOWNGDG
  asreml writes this file, runs your program and then reads
  which it presumes has the following format:
  The first lines should agree with the top of this file
  specifying the order of the matrices         (   15)
             the number of variance parameters (    2)
       and a control parameter you can specify (    1).
  These are written in (3I5) format.  They are followed by
  the list of variance parameters written in (6D13.7) format.
  Follow this with     3 matrices written in (6D13.7) format.
  These are to be each of   120 elements being lower triangle
  row-wise of the G matrix and its derivatives with respect
  to the parameters in turn.

This file contains details about what is expected in the file written by your program. The filename used has the same basename as the job you are running with extension .own for the file written by ASReml and .gdg for the file your program writes. The type of the parameters is set with the !T qualifier described below. The control parameter is set using the !F qualifier.

  • !F2 applies to OWN models. With OWN, the argument of !F is passed to the MYOWNGDG program as an argument the program can access. This is the mechanism that allows several OWN models to be fitted in a single run.
  • !Ts is used to set the type of the parameters. It is primarily used in conjunction with the OWN structure as ASReml knows the type in other cases. The valid type codes are as follows:
    Code Description Action with !GP
    V variance forced positive
    G variance ratio forced positive
    R correlation -1 < r < 1
    C covariance
    P positive correlation      0 < r < 1
    L loading
    This coding also affects whether the parameter is scaled by the residual variance in the output.

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