DIAGNOSTIC(S) FROM PARSER:
Info: left-hand side variable (name=SigmaOffDiag) occurs on right-hand side of assignment, causing inefficient deep copy to avoid aliasing.
Info: left-hand side variable (name=y_hat) occurs on right-hand side of assignment, causing inefficient deep copy to avoid aliasing.
https://discourse.mc-stan.org/t/deep-copy-warning/885/11