Finish support for 4th order accuracy.

ABI and API break.

1 files changed, 8 insertions, 2 deletions

diff --git a/mg2d.h b/mg2d.h
index a0c0c70..4ccb5da 100644
--- a/mg2d.h
+++ b/mg2d.h
@@ -108,14 +108,20 @@ typedef struct MG2DBoundary {
     /**
      * For type = MG2D_BC_TYPE_FIXVAL:
      *     Values of the unknown function on the boundary.
+     *     The number of boundary layers is equal to fd_stencil.
+     *     The first boundary layer has the number of points equal to the
+     *     corresponding domain_size. Each subsequent boundary layer has one
+     *     more boundary point at each end of the domain.
      *
      * Ignored otherwise.
      */
     double *val;
     /**
-     * Number of elements in val.
+     * Number of elements between rows in val. I.e. if val[0] is the first
+     * boundary point, then val[val_stride - 1] is the first boundary point in
+     * the second row and so on.
      */
-    size_t  val_len;
+    size_t  val_stride;
 } MG2DBoundary;
 
 typedef struct MG2DContext {