Add NaNHelper utility

The aim of this helper is to allow to print signaling NaN. This should help to debug uninitialized matrices of vectors values while printing them.

src/algebra/DenseMatrix.hpp

@@ -9,6 +9,8 @@
 #include <utils/PugsUtils.hpp>
 #include <utils/Types.hpp>
 
+#include <iostream>
+
 template <typename DataType>
 class DenseMatrix   // LCOV_EXCL_LINE
 {
@@ -246,6 +248,19 @@ class DenseMatrix   // LCOV_EXCL_LINE
   PUGS_INLINE
   DenseMatrix& operator=(DenseMatrix&&) = default;
 
+  friend std::ostream&
+  operator<<(std::ostream& os, const DenseMatrix& A)
+  {
+    for (size_t i = 0; i < A.numberOfRows(); ++i) {
+      os << i << '|';
+      for (size_t j = 0; j < A.numberOfColumns(); ++j) {
+        os << ' ' << j << ':' << NaNHelper(A(i, j));
+      }
+      os << '\n';
+    }
+    return os;
+  }
+
   template <typename DataType2>
   DenseMatrix(const DenseMatrix<DataType2>& A)
   {