IsCP

IsCP is a function that determines whether or not a given superoperator is completely positive.

Syntax

 * CP = IsCP(PHI)
 * CP = IsCP(PHI,TOL)

Argument descriptions

 * PHI: A superoperator. Should be provided as either a Choi matrix, or as a cell with either 1 or 2 columns (see the tutorial page for more details about specifying superoperators within QETLAB).
 * TOL (optional, default eps^(3/4)): The numerical tolerance used when determining complete positivity.

Examples
The following code verifies that the map $\Phi$ defined by $\Phi(X) = X - UXU^*$ is not completely positive, where $U = \frac{1}{\sqrt{2}}\begin{bmatrix}1 & 1 \\ -1 & 1\end{bmatrix}$.