A stable shifted-legendre projection scheme for generating PN boundary conditions

A projection scheme for generating PN boundary conditions based on the shifted Legendre polynomials is discussed. The projection scheme yields N+l conditions for each boundary of a slab, just twice the number of conditions required, The resulting overdetermined system of equations is subsequently reduced to a square system by means of a standard least-squares technique. Tests carried out for several problems indicate that the procedure is numerically stable in high-order, in contrast to the findings of some years ago when a similar projection scheme was first proposed