Produces derivatives of induced velocity by Surf_in w.r.t. the zetac point. Derivatives are divided into those associated to the movement of zetac, and to the movement of the Surf_in vertices (DerVert).
If Surf_in is bound (IsBound==True), the circulation over the TE due to the wake is not included in the input.
If Surf_in is a wake (IsBound==False), derivatives w.r.t. collocation points are computed ad the TE contribution on DerVert. In this case, the chordwise paneling Min_bound of the associated input is required so as to calculate Kzeta and correctly allocate the derivative matrix.
The output derivatives are: - Dercoll: 3 x 3 matrix - Dervert: 3 x 3*Kzeta (if Surf_in is a wake, Kzeta is that of the bound)
Warning: zetac must be contiguously stored!