1. Evolution from VBA V1 to V2 (Numerics)

2. Main program: Version V1.2
Do While ctrl.t < ctrl.tend
'Sets new time and zeros coefficients
ctrl.t = ctrl.t + ctrl.dt
ctrl.TimeDays = ctrl.t / 86400
Call ZerosCoeffs(Coef, gr)
' Call LightUpdate(Light, ctrl, gr, Pr)
' If Not (Pr.Temperature.Calc_As.Method = "Evolution") Then
' Call CalcTempIfnotEvolution(Pr.Temperature, gr, ctrl)
' End If
' Performs transport
Call CoefTransport(flow, gr.NC, ctrl, Coef)
If (ctrl.Explicit) Then
Call ExpTransport(Pr.Generic, Coef, gr.NC)
Else
Main program: Version V1.2
Else
MsgBox ("Implicit not programed in this version")
End
End If
' Performs discharges
Call ApplyDischarges(Pr.Generic, gr, ctrl.dt)
' Call ApplyDischarges(Pr.Temperature, gr, ctrl.dt)
'Updates concentrations with sources and sinks in Phyto, Zoo and Detritus properties
'and Nutrient property
If (ctrl.Explicit) Then
Call ExpSinksGeneric(Pr.Generic, gr.NC, ctrl.dt)
Call ImpSinksGeneric(Pr.Generic, gr.NC, ctrl.dt)

3. Sub CoefTransport(flow As Flow_properties, NC As Integer, ctrl As Controls, Coef As Equation_Coef)
Dim I As Integer
If ctrl.Diffusion Then
………
End If
If ctrl.Advection Then
If ctrl.AdvType = "upwind" Then ' Advection Upwind
……..
ElseIf ctrl.AdvType = "central" Then
For I = 2 To NC - 1
Coef.LeftCoef(I) = Coef.LeftCoef(I) + flow.CourantNr / 2
Coef.RigthCoef(I) = Coef.RigthCoef(I) - flow.CourantNr / 2
Next

4. ' Even with central differences upwind has to be used at the boundaries
If flow.Velocity > 0 Then
Coef.LeftCoef(NC) = Coef.LeftCoef(NC) + flow.CourantNr
Coef.CenterCoef(NC) = Coef.CenterCoef(NC) - flow.CourantNr
Coef.LeftCoef(1) = Coef.LeftCoef(1) + flow.CourantNr
Coef.CenterCoef(1) = Coef.CenterCoef(1) - flow.CourantNr
Else
Coef.CenterCoef(1) = Coef.CenterCoef(1) + flow.CourantNr
Coef.RigthCoef(1) = Coef.RigthCoef(1) - flow.CourantNr
Coef.CenterCoef(NC) = Coef.CenterCoef(NC) + flow.CourantNr
Coef.RigthCoef(NC) = Coef.RigthCoef(NC) - flow.CourantNr
End If
MsgBox "Advection Type not defined:" & ctrl.AdvType
End Sub