Set matrix to zero before inserting entries (partially fixes bug 539).
Set matrix to zero before inserting entries (partially fixes bug 539).

mjbshaw/Eigen,madlib/eigen_backup,rotorliu/eigen,madlib/eigen_backup,rotorliu/eigen,mjbshaw/Eigen,rotorliu/eigen,madlib/eigen_backup,mjbshaw/Eigen,rotorliu/eigen,madlib/eigen_backup,mjbshaw/Eigen