COUPLING_COEFFICIENT
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Positive coupling magnitude for this device within its coupling group.
The scheduler couples the power flows of all devices in the group: each device's power is its coupling coefficient times the group's common flow level.
The flow direction of each device is inferred from its directional capacities: a device with ``consumption-capacity: "0 kW"`` is an output (producing) device, and a device with ``production-capacity: "0 kW"`` is an input (consuming) device.
Exactly one of the two directional capacities must be set to a fixed zero for each coupled device.
For example, a CHP unit with 50% thermal and 30% electrical efficiency uses a gas input device (coefficient 1), a heat output device (coefficient 0.5) and an electricity output device (coefficient 0.3).
Defaults to 1.