Loadable Function: [vxg, vyg, vx0, vy0] = vitensor (alfa, xAC, yAC, zAC, sym)

Computes the induced velocities tensors on a lifting line approximated by a chain of vortex segments. alfa is the angle of attack (relative to x-z plane), xAC, yAC, zAC are coordinates of the lifting line points (chordwise, vertical, spanwise). sym denotes symmetry - only half of the lifting line is given, the other half is obtained by mirroring by the xy plane. On return, vxg and vyg are jacobians of induced local x and y velocities - the velocities induced by j-th vortex on i-th collocation point are given by vxg(i,j), vyg(i,j). vx0(i), vy0(i) denote local velocities induced on the collocation point by freestream. Thus, if gam is a vector of panel circulations, the corresponding induced velocities can be calculated as vx = vxg*gam+vx0; vy = vyg*gam+vy0;