Added the find_min_and_max() function. I also changed the code in the

lu_decomposition::is_singular() function to avoid what appears to be a
bug in gcc 4.2.4 that caused one of the regression tests to segfault
when built with -O3.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402873

dlib/matrix/matrix_lu.h

@@ -215,13 +215,15 @@ namespace dlib
             << "\n\tthis: " << this
             );
 
-        type eps = max(abs(diag(LU)));
+        type max_val, min_val;
+        find_min_and_max (abs(diag(LU)), min_val, max_val);
+        type eps = max_val;
         if (eps != 0)
             eps *= std::sqrt(std::numeric_limits<type>::epsilon())/10;
         else
             eps = 1;  // there is no max so just use 1
 
-        return min(abs(diag(LU))) < eps;
+        return min_val < eps;
     }
 
 // ----------------------------------------------------------------------------------------

dlib/matrix/matrix_utilities.h

@@ -20,6 +20,39 @@
 namespace dlib
 {
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename EXP
+        >
+    void find_min_and_max (
+        const matrix_exp<EXP>& m,
+        typename EXP::type& min_val,
+        typename EXP::type& max_val
+    )
+    {
+        DLIB_ASSERT(m.size() > 0, 
+            "\ttype max(const matrix_exp& m)"
+            << "\n\tYou can't ask for the max() of an empty matrix"
+            << "\n\tm.size():     " << m.size() 
+            );
+        typedef typename matrix_exp<EXP>::type type;
+
+        min_val = m(0,0);
+        max_val = min_val;
+        for (long r = 0; r < m.nr(); ++r)
+        {
+            for (long c = 0; c < m.nc(); ++c)
+            {
+                type temp = m(r,c);
+                if (temp > max_val)
+                    max_val = temp;
+                if (temp < min_val)
+                    min_val = temp;
+            }
+        }
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/matrix/matrix_utilities_abstract.h

@@ -621,6 +621,23 @@ namespace dlib
             - returns the value of the biggest element of m
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    void find_min_and_max (
+        const matrix_exp& m,
+        matrix_exp::type& min_val,
+        matrix_exp::type& max_val
+    );
+    /*!
+        requires
+            - m.size() > 0
+        ensures
+            - #min_val == min(m)
+            - #max_val == max(m)
+            - This function computes both the min and max in just one pass
+              over the elements of the matrix m.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     const matrix_exp::type sum (