By following the original derivation of GGA, pressure dependent demand formula can be solved as:

The difference from the original GGA is the new diagonal matrix D22, which is the deviation of A22 of pressure head H.

The modified GGA is to calculate D22 for each pressure dependent demand node and add at A(i, i) as follows:

where j denotes the pipe j that is connected with node i. This notation is the same as the EPANET2 engine code.