From 91c352d4ca45042055ee0205f46e815b6e89a631 Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Tue, 29 Jan 2019 12:54:06 +0100
Subject: mg2d: fail when a full multigrid iteration does not reduce the
 residual

---
 mg2d.c | 5 +++++
 1 file changed, 5 insertions(+)

(limited to 'mg2d.c')

diff --git a/mg2d.c b/mg2d.c
index 902c3cc..a65af6c 100644
--- a/mg2d.c
+++ b/mg2d.c
@@ -527,6 +527,11 @@ int mg2d_solve(MG2DContext *ctx)
         mg2di_log(&priv->logger, MG2D_LOG_VERBOSE,
                   "finished toplevel iteration %d, residual %g -> %g (%g)\n",
                   i, res_prev, res_cur, res_prev / res_cur);
+        if (res_cur / res_prev > 1.0) {
+            mg2di_log(&priv->logger, MG2D_LOG_ERROR, "A multigrid iteration diverged\n");
+            ret = MG2D_ERR_DIVERGE;
+            goto fail;
+        }
         res_prev = res_cur;
     }
 
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