Functionality of nconstrain with the MHRM algorithm

[Emre Alagöz]

Dear Phil and all,

I have a quick question regarding the use of nconstrain, as the subject tells it. I am using mirt to fit a multidimensional Item Response Tree (IRTree) model, but the model does not matter for the question I have (just putting it here so that others who search this could find this topic as well). 

When I use the EM algorithm, I can easily use the nconstrain to specify equality constraints with sign difference on the factor loadings, e.g., a1 = -a2. However, it does not work when I switch to MHRM algorithm. 

Is there a workaround or plan to make it possible with the MHRM? 

I know one option is to use createItem. However, since I later extract the score contributions with the estfun.AllModelClass() to test parameter heterogeneity with score-based recursive algorithm, this workaround is not suitable for me.

Thank you very much in advance for taking your time. 

Best wishes,

Emre