adding caching? 

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/aqr@45 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
latest version. 

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/aqr@46 edb9625f-4e0d-4859-8d74-9fd3b1da38cb