# HG changeset patch
# User Rik <rik@octave.org>
# Date 1444228904 25200
# Node ID f61c67865d9fe1d09b3d46766c8c962e8d00c352
# Parent  ea6a1c00763adf9c6ee19cc25554b35f6a1a6c0c
Don't return A for inv (A) when A is a singular Diagonal matrix (bug #46103).

* dDiagMatrix.cc (inverse), fDiagMatrix.cc (inverse): return octave_Inf for the
inverse of a diagonal element whose value is 0.

* test/diag-perm.tst: Add tests for new behavior.

diff -r ea6a1c00763a -r f61c67865d9f liboctave/array/dDiagMatrix.cc
--- a/liboctave/array/dDiagMatrix.cc	Tue Oct 06 22:14:41 2015 +0200
+++ b/liboctave/array/dDiagMatrix.cc	Wed Oct 07 07:41:44 2015 -0700
@@ -280,10 +280,7 @@
   for (octave_idx_type i = 0; i < len; i++)
     {
       if (elem (i, i) == 0.0)
-        {
-          info = -1;
-          return *this;
-        }
+        retval.elem (i, i) = octave_Inf;
       else
         retval.elem (i, i) = 1.0 / elem (i, i);
     }
diff -r ea6a1c00763a -r f61c67865d9f liboctave/array/fDiagMatrix.cc
--- a/liboctave/array/fDiagMatrix.cc	Tue Oct 06 22:14:41 2015 +0200
+++ b/liboctave/array/fDiagMatrix.cc	Wed Oct 07 07:41:44 2015 -0700
@@ -280,10 +280,7 @@
   for (octave_idx_type i = 0; i < len; i++)
     {
       if (elem (i, i) == 0.0)
-        {
-          info = -1;
-          return *this;
-        }
+        retval.elem (i, i) = octave_Inf;
       else
         retval.elem (i, i) = 1.0 / elem (i, i);
     }
diff -r ea6a1c00763a -r f61c67865d9f test/diag-perm.tst
--- a/test/diag-perm.tst	Tue Oct 06 22:14:41 2015 +0200
+++ b/test/diag-perm.tst	Wed Oct 07 07:41:44 2015 -0700
@@ -263,3 +263,10 @@
 %! A = A * I () + A;
 %! A(6, 4) = nan ();
 %! assert (full (D - A), D - full (A));
+
+## inverse preserves diagonal structure even for singular matrices (bug #46103)
+%!test
+%! x = diag (1:3);
+%! assert (inv (x), diag ([1 1/2 1/3]));
+%! x = diag (0:2);
+%! assert (inv (x), diag ([Inf 1 1/2]));