Modified GGA Solution
By following the original derivation of GGA, pressure dependent demand formula can be solved as:
![](GUID-D5F61834FD3142F8B4592A5019D38B3B-low.png)
The difference from the original GGA is the new diagonal matrix D22, which is the deviation of A22 of pressure head H.
![](GUID-FAAE77D20804406FBDCC84EDF634B82F-low.png)
The modified GGA is to calculate D22 for each pressure dependent demand node and add at A(i, i) as follows:
![](GUID-98311FF8688942978D0F0C8B5786AF3F-low.png)
where j denotes the pipe j that is connected with node i. This notation is the same as the EPANET2 engine code.