Fix compilation of doc

doc/examples/Cwise_erf.cpp

@@ -0,0 +1,9 @@
+#include <Eigen/Core>
+#include <unsupported/Eigen/SpecialFunctions>
+#include <iostream>
+using namespace Eigen;
+int main()
+{
+  Array4d v(-0.5,2,0,-7);
+  std::cout << v.erf() << std::endl;
+}

doc/examples/Cwise_erfc.cpp

@@ -0,0 +1,9 @@
+#include <Eigen/Core>
+#include <unsupported/Eigen/SpecialFunctions>
+#include <iostream>
+using namespace Eigen;
+int main()
+{
+  Array4d v(-0.5,2,0,-7);
+  std::cout << v.erfc() << std::endl;
+}

doc/examples/Cwise_lgamma.cpp

@@ -0,0 +1,9 @@
+#include <Eigen/Core>
+#include <unsupported/Eigen/SpecialFunctions>
+#include <iostream>
+using namespace Eigen;
+int main()
+{
+  Array4d v(0.5,10,0,-1);
+  std::cout << v.lgamma() << std::endl;
+}

doc/snippets/Cwise_erf.cpp

@@ -1,2 +0,0 @@
-Array4d v(-0.5,2,0,-7);
-cout << v.erf() << endl;

doc/snippets/Cwise_erfc.cpp

@@ -1,2 +0,0 @@
-Array4d v(-0.5,2,0,-7);
-cout << v.erfc() << endl;

doc/snippets/Cwise_lgamma.cpp

@@ -1,2 +0,0 @@
-Array4d v(0.5,10,0,-1);
-cout << v.lgamma() << endl;