# SingleContour¶

class SingleContour(direction=<class 'NL.ComputerScienceUtilities.NLFlag._NLFlag.Left'>)

A simple flag-like class representing either a left or right single contour.

Parameters: direction (NLFlag.Left | NLFlag.Right) – The direction to use in this SingleContour. Default: NLFlag.Left
direction()
Returns: The directions. NLFlag.Left | NLFlag.Right

## Notes¶

For systems with a finite bias there are equivalent ways to obtain the density matrix (see Notes). In principle the left and right estimates of the density matrix are equivalent, but differ in practice because of the approximate integration. The SingleContour object is used to specify which one to use.

When:

contour_parameters = ContourParameters(method=SingleContour(direction=Left))


is specified, the density matrix is calculated as:

$D = D^L + \Delta^R~.$

If, however:

contour_parameters = ContourParameters(method=SingleContour(direction=Right))


is specified, the left non-equilibirum contribution is used:

$D = D^R + \Delta^L~.$