# Red-Black Neighbourhood Stencil Diagrams (for Laplace)

In a previous blog Repa Laplace and SOR, I used Repa to implement a Laplace solver using the Red-Black scheme. The explanation of alternating stencils probably needed a diagram, so here it is.

This diagram illustrates the shapes of the stencils for adding neighbours of red and black cells. It shows that two different stencils are needed (for odd and even rows) and these are swapped over for red and black.

(The diagram was produced with Haskell Diagrams)