calc_branch_angle

calc_branch_angle(mpc)

calc_branch_angle() - Calculate branch angle differences across active branches

DELTA = CALC_BRANCH_ANGLE(MPC)

Calculates the angle difference (in degrees) across all active branches
in the MATPOWER case. Angles are calculated as the difference between
the FROM bus and the TO bus.

Input:
    MPC   - MATPOWER case struct (can have external bus numbering)

Output:
    DELTA - nl x 1 vector of branch angle differences Af - At, where
            Af and At are vectors of voltage angles at "from" and "to"
            ends of each line respectively. DELTA is 0 for out-of-service
            branches.