New Feature Proposals

At the end of the last developers meeting, it was tentatively agreed that we should discuss the feature set for the OpenMx 1.0 release. I propose to make that issue the primary topic for the next developers meeting, on 3/19/10. Of course if something critical comes up this week, we can push the topic forward a week. Logistically, we should have this conversation soon as we are planning a June date for the OpenMx 1.0 release.

Developers: remind ourselves of the feature set promised in the grant. High probability these features will have greatest priority.

Hi
Any chance we could get crosstab or weighted response vector data types ?
these are very useful for obtaining starting values for larger FIML ordinal analyses
thanks
Sarah

(by weighted response vector data I mean data that looks something like this
v1 v2 v3 v4 v5 v6 freq
0 0 0 0 0 0 100
0 0 0 0 0 1 100
...
)

This is based on an old classicMx trick that I used a lot in writing stealth model code

I think you can constrain the calculated matrix to be equal to a free matrix and the obtain CIs on the free matrix. for example:

mxMatrix( type="Full", nrow=nvar, ncol=nf, free=TRUE, values=.3, name="factor" ),
mxMatrix( type="Diag", nrow=nvar, ncol=nvar, free=TRUE, values=.3, name="residual" ),
mxMatrix( type="Stand", nrow=nvar, ncol=nvar, free=TRUE, name="Vconstraint" ),
mxAlgebra( expression=((factor %*% t(factor))+(residual%*% t(residual))), name="expCov" ),

Two suggestions have been proposed by smedland for improving the specification of ordinal models. I support both of these suggestions, and encourage OpenMx users to leave their feedback on these proposed changes.

1. Allow neighboring duplicate values to exist within a column of the thresholds matrix. CURRENT: a column must consist of strictly increasing values. CHANGE: a column must consist of non-decreasing values. Internally, neighboring duplicate values are collapsed into a single threshold.

In the next binary release** you will be able to use ranges and subranges in MxAlgebra expression. The range operator "x : y" creates a column vector of elements [x, x+1, x+2, ..., y]. In addition, the square bracket operator now supports subranges. The following are now valid MxAlgebra expressions:

foo <- mxAlgebra(bar[1:2, 3:4], name = 'foo')
foo <- mxAlgebra(bar[1:2, 1], name = 'foo')
foo <- mxAlgebra(bar[1:2, ], name = 'foo')
foo <- mxAlgebra(bar[cbind(1,3,5), ], name = 'foo') # select odd rows

It was suggested at last week's developers meeting that it could be useful to use the extract operator for MxMatrix objects. So I've implemented foo[x,y] and foo[x,y] <- z where 'foo' is a MxMatrix object. The new feature has been checked into the subversion repository.

Some notes about foo[x,y]

• returns a MxMatrix object
• applies [x,y] extraction to the components of foo (values, labels, free, lbound, ubound)
• returns a MxMatrix of the same type as foo, unless that would cause an error. In cases of errors, return a Full matrix.

This proposal is for a new objective function that allows for a generic row-by-row computation on a data-set, followed by a final computation to aggregate all the row-by-row results. The objective function takes four arguments.

mxRowObjective(rowAlgebra, rowResults = NA, reduceAlgebra = NA, name = NA).