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.
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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.
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In a FIML objective function, if thresholds are specified and expected means are not specified, then internally create an expected means vector of 0's. CURRENT: all FIML objectives require an expected means vector. CHANGE: FIML objectives with thresholds do not require means.
In addition to these two proposed changes by Sarah, I have two additional proposals of my own. These are intended to simplify the current interface.
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Eliminate using NAs at the end of columns in the thresholds matrices. Contingent on proposal (1), use duplicate values to fill a column instead of NAs. Possibly use +Inf at the bottom of columns.
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Eliminate the possibility of multiple threshold matrices. I find this interface confusing and prone to errors.