Make Vector output more readable and use NaNHelper

src/algebra/Vector.hpp

@@ -2,6 +2,7 @@
 #define VECTOR_HPP
 
 #include <utils/Array.hpp>
+#include <utils/NaNHelper.hpp>
 #include <utils/PugsAssert.hpp>
 #include <utils/PugsMacros.hpp>
 #include <utils/PugsUtils.hpp>
@@ -28,8 +29,11 @@ class Vector   // LCOV_EXCL_LINE
   friend std::ostream&
   operator<<(std::ostream& os, const Vector& x)
   {
-    for (size_t i = 0; i < x.size(); ++i) {
-      os << ' ' << x[i];
+    if (x.size() > 0) {
+      os << 0 << ':' << NaNHelper(x[0]);
+    }
+    for (size_t i = 1; i < x.size(); ++i) {
+      os << ' ' << i << ':' << NaNHelper(x[i]);
     }
     return os;
   }

tests/test_Vector.cpp

@@ -371,8 +371,9 @@ TEST_CASE("Vector", "[algebra]")
     std::ostringstream vector_ost;
     vector_ost << x;
     std::ostringstream ref_ost;
-    for (size_t i = 0; i < x.size(); ++i) {
-      ref_ost << ' ' << x[i];
+    ref_ost << 0 << ':' << x[0];
+    for (size_t i = 1; i < x.size(); ++i) {
+      ref_ost << ' ' << i << ':' << x[i];
     }
     REQUIRE(vector_ost.str() == ref_ost.str());
   }