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Q.matrix() ( i.e. the .matrix() operation) returns
matrix() Returns the Hessian matrix A for which Q(X) = (1/2)∗Xt∗A∗X(1/2)∗Xt∗A∗X.
I can understand where the two comes from if your doing differentiation.
What I don't understand is why .matrix() gives this form. Ray