From ea62eb612ebf08fee28c4fbb009ee24b0cf4079b Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Thu, 13 Jun 2019 12:01:23 +0200
Subject: mg2d: add API for specifying singular diff coeffs at the boundaries

API and ABI break.
---
 mg2d.h | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 63 insertions(+), 5 deletions(-)

(limited to 'mg2d.h')

diff --git a/mg2d.h b/mg2d.h
index 47d709e..2f593bc 100644
--- a/mg2d.h
+++ b/mg2d.h
@@ -29,6 +29,68 @@
 
 typedef struct MG2DInternal MG2DInternal;
 
+/**
+ * Flags for diff coeffs boundary specifications.
+ */
+enum MG2DDCFlag {
+    /**
+     * The coefficients have a discontinuity at the boundary, i.e.
+     * C(x, y) = C0(x, y) + D(x, y),
+     * where C is the resulting value used for the solve, C0 is continuous
+     * everywhere, and D is zero everywhere except along the boundary. D is
+     * assumed to be continuous along the boundary.
+     *
+     * The values of D should be stored in MG2DDCBoundarySpec.val
+     */
+    MG2D_DC_FLAG_DISCONT = (1 << 0),
+    /**
+     * The coefficients have a first order pole at the boundary, i.e.
+     * C(x, y) · (x_i - x_i^0)                  (1)
+     * is continuous, where C is the actual value of the coefficient, x_i is the
+     * coordinate which is constant along the boundary and x_i^0 is the value of
+     * that coordinate along the boundary.
+     *
+     * The value of (1) along the boundary should be stored in
+     * MG2DDCBoundarySpec.val.
+     */
+    MG2D_DC_FLAG_POLE    = (1 << 1),
+};
+
+/**
+ * Specification of the behaviour of differential equation coefficients on a
+ * boundary.
+ */
+typedef struct MG2DDCBoundarySpec {
+    /**
+     * A combination of MG2DDCFlag
+     */
+    int flags;
+    /**
+     * Value determined by flags. Need not be filled if the flags are zero.
+     */
+    double *val;
+} MG2DDCBoundarySpec;
+
+/**
+ * Specification of a single coefficient of the PDE.
+ */
+typedef struct MG2DDiffCoeffs {
+    /**
+     * Values of the coefficient at the grid points. Values corresponding to
+     * successive x locations are contiguous in memory.
+     */
+    double         *data;
+    /**
+     * Number of elements between successive y locations in data.
+     */
+    ptrdiff_t       stride;
+
+    /**
+     * Behaviour of the coefficient on the boundaries.
+     */
+    MG2DDCBoundarySpec boundaries[4];
+} MG2DDiffCoeffs;
+
 typedef struct MG2DContext {
     /**
      * Solver private data, not to be accessed in any way by the caller.
@@ -127,11 +189,7 @@ typedef struct MG2DContext {
      * Allocated by the solver in mg2d_solver_alloc(), owned by the solver.
      * Must be filled by the caller before solving.
      */
-    double   *diff_coeffs[MG2D_DIFF_COEFF_NB];
-    /**
-     * Distance between neighbouring gridpoints along coord1.
-     */
-    ptrdiff_t diff_coeffs_stride;
+    MG2DDiffCoeffs *diff_coeffs[MG2D_DIFF_COEFF_NB];
 
     /**
      * Number of threads to use for processing.
-- 
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