  In general the calculation of robustness of entanglement for the mixed
entangled quantum states is rather difficult to handle analytically. Using the
the convex semi-definite programming method, the robustness of entanglement of
some mixed entangled quantum states such as: $2\otimes 2$ Bell decomposable
(BD) states, a generic two qubit state in Wootters basis, iso-concurrence
decomposable states, $2\otimes 3$ Bell decomposable states, $d\otimes d$ Werner
and isotropic states, a one parameter $3\otimes 3$ state and finally multi
partite isotropic state, is calculated exactly, where thus obtained results are
in agreement with those of :$2\otimes 2$ density matrices, already calculated
by one of the authors in \cite{Bell1,Rob3}. Also an analytic expression is
given for separable states that wipe out all entanglement and it is further
shown that they are on the boundary of separable states as pointed out in
\cite{du}.
  {\bf Keywords: Robustness of entanglement, Semi-definite programming, Bell
decomposable states, Werner and isotropic states.}
