Hi,
I tried to use your code, so I could do some algebric operations on matrices.
I included <Eigen/Core> but a lot of errors appeared.

here are some of them:

Error 44 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int c:\users\win7\desktop\eigen-eigen-1306d75b4a21\eigen\src\core\productbase.h 183 1 AdiAdi

Error 45 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int c:\users\win7\desktop\eigen-eigen-1306d75b4a21\eigen\src\core\productbase.h 183 1 AdiAdi

Error 41 error C3855: 'Eigen::internal::nested': template parameter 'PlainObject' is incompatible with the declaration c:\users\win7\desktop\eigen-eigen-1306d75b4a21\eigen\src\core\productbase.h 184 1 AdiAdi

etc.

I don't even know how to start resolving these errors..
can you help me,please?

What's you compiler? version? system? compilation flags?

I'm not sure I know what you mean..but I use visual studio.
did I answer your question?

It's working well here, so please specify the the versions of visual studio and Eigen. Please, also show the complete code example you are trying to compile. Maybe you are including bad headers before including Eigen. Or perhaps you are using weird compilation flags.

I use visual Studio 2010 and I downloaded Eigen 3.2.2 release. The errors started when I included <Eigen/Core>, not before.

Please provides a self-contained example as everything is working well for us and other VS2010 users.