1 files changed, 10 insertions, 2 deletions
diff --git a/mg2d.h b/mg2d.h
index 867d77e..01698a8 100644
--- a/mg2d.h
+++ b/mg2d.h
@@ -163,7 +163,9 @@ typedef struct MG2DContext {
      * Allocated and initialized to zero by the solver in mg2d_solver_alloc(),
      * owned by the solver.
      * May be filled by the caller before solving to set the initial guess.
-     * Afterwards updated in mg2d_solve().
+     * Afterwards updated by mg2d_solve() if it returns 0,
+     * MG2D_ERR_MAXITER_REACHED or MG2D_ERR_DIVERGE. If mg2d_solve() returnes
+     * another error code, the contents of u are unspecified.
      */
     double   *u;
     /**
@@ -265,7 +267,13 @@ MG2DContext *mg2d_solver_alloc_mpi(MPI_Comm comm, const size_t local_start[2],
  *
  * This function may be called more than once.
  *
- * @return 0 on success, a negative error code on failure.
+ * @return
+ *   - 0 on success
+ *   - MG2D_ERR_MAXITER_REACHED if desired tolerance was not reached after
+ *     maximum allowed number of iterations were performed. The final
+ *     value of the solution is still exported in ctx->u.
+ *   - MG2D_ERR_DIVERGE if the iteration process has diverged.
+ *   - another negative error code on other types of failure
  */
 int mg2d_solve(MG2DContext *ctx);
 /**