fix compilation of the doc and started a page dedicated to high performance and or BLAS users
diff --git a/doc/snippets/MatrixBase_part.cpp b/doc/snippets/MatrixBase_part.cpp
index 6f393a1..81e66c4 100644
--- a/doc/snippets/MatrixBase_part.cpp
+++ b/doc/snippets/MatrixBase_part.cpp
@@ -1,3 +1,5 @@
+#warning deprecated
+/*
Matrix3d m = Matrix3d::Zero();
m.part<Eigen::StrictlyUpperTriangular>().setOnes();
cout << "Here is the matrix m:" << endl << m << endl;
@@ -6,3 +8,4 @@
Matrix3d n;
n.part<Eigen::SelfAdjoint>() = (m*m.adjoint()).lazy();
cout << "The result is:" << endl << n << endl;
+*/
\ No newline at end of file