Compute the flux associated with the Scharfetter-Gummel approximation of the scalar field u.
The vector field is defined as:
J(u) = alpha* gamma * (eta * grad u - beta * u))
where alpha is an element-wise constant scalar function, eta and gamma are piecewise linear conforming scalar functions, while beta is element-wise constant vector function.
J(u) is an element-wise constant vector function.
Instead of passing the vector field beta directly one can pass a piecewise linear conforming scalar function phi as the last input. In such case beta = grad phi is assumed. If phi is a single scalar value beta is assumed to be 0 in the whole domain.
See also: bim2c_pde_gradient,bim2a_advection_diffusion.
Package: bim