# HG changeset patch
# User Rik <rik@octave.org>
# Date 1626967632 25200
# Node ID e7c10a552ecc49f9de9b503124976eba0e0fcb1b
# Parent  ad023dbe9606dde0eed61c63f9a37d864d7d83f1
Emit more informative error message when ARPACK fails to converge (bug #60924)

* eigs-base.cc (arpack_errno2str): For errno=-14 (failure to converge), emit a
warning that suggests possible solutions.  Correct typo where variable "errno"
was used where "errnum" was desired.

diff -r ad023dbe9606 -r e7c10a552ecc liboctave/numeric/eigs-base.cc
--- a/liboctave/numeric/eigs-base.cc	Thu Jul 22 08:03:41 2021 -0700
+++ b/liboctave/numeric/eigs-base.cc	Thu Jul 22 08:27:12 2021 -0700
@@ -157,6 +157,8 @@
       else if (fcn_name.compare ("dseupd") == 0)
         msg = "DSAUPD did not find any eigenvalues to sufficient accuracy.";
 
+      msg += "  Consider changing tolerance (TOL), maximum iterations (MAXIT), number of Lanzcos basis vectors (P), or starting vector (V0) in OPTS structure.";
+
       break;
 
     case -15:
@@ -207,9 +209,8 @@
 
     }
 
-  if ((errno != -9) & (errno != -14) & (errno != -9999))
-    // This is a bug in Octave interface to ARPACK
-    msg.append (bug_msg);
+  if ((errnum != -9) && (errnum != -14) && (errnum != -9999))
+    msg.append (bug_msg);  // This is a bug in Octave interface to ARPACK
 
   return msg;
 }