Your attempt to terminate loops early eliminates the opportunity to find
legitimate answers.

This appears to get all the answers and is faster than the unconstrained
version:

I didn't change them, but if you want 3 variables to be doubles, you can't
use

Dim a, b, c as double

you must use

Dim as as Double, b as Double, c as Double

in the original, a and b are variants.

Sub PumpFlowCombinationVer2()

' This Macro generates all possible combinations of flow distribution
' between pumps to meet required System Flow.
' Divisions of 0.1m(^3)are used.

' Please feed in the necessary parameters before running the Macro.

' Good Day!


'''''''''''''''''''''''' Declarations
'''''''''''''''''''''''''''''''''''''''''''

Dim x As Double

Dim Qsummax As Double

Dim Qsys, Q1, Q2, Q3, Q4, Q5 As Double

' Upper boundary conditions for flows
Dim Q1max, Q2max, Q3max, Q4max, Q5max As Double

' Lower boundary conditions for flows
Dim Q1min, Q2min, Q3min, Q4min, Q5min As Double

' Counters
Dim b, c, d, e, f As Double

' Temporary variables
Dim Qtemp As Double


'''''''''''''''''''''''' Initialization
'''''''''''''''''''''''''''''''''''''''''''



' Assigning System Flow
Qsys = Round(Range("Interface!B6"), 1)

''''''''''''''''''''''''''''''''''''''''''''''''' TO BE REMOVED -TESTING
ONLY

Qsys = 0.6

' Assigning Boundary Flow Values
Q1max = Range("Input!B10")
Q2max = Range("Input!C10")
Q3max = Range("Input!D10")
Q4max = Range("Input!E10")
Q5max = Range("Input!F10")


Q1min = Range("Input!B11")
Q2min = Range("Input!C11")
Q3min = Range("Input!D11")
Q4min = Range("Input!E11")
Q5min = Range("Input!F11")


' Assigning Counter Initial Values (To be placed after Qmin initialization)
b = Q1min
c = Q2min
d = Q3min
e = Q4min
f = Q5min



x = 4

'''''''''''''''''''''''' Main Body
''''''''''''''''''''''''''''''''''''''''''''''''


Qsummax = Q1max + Q2max + Q3max + Q4max + Q5max

If (Qsys > Qsummax) Then

MsgBox "System Flow requirements exceed total pump capacity. Please run all
pumps at full speed. Insufficient System Flow is being provided at present."


Else

Do While Application.Round(b, 1) <= Q1max And _
(Qsys - b - c - d - e - f) > -0.001 Or _
(Qsys - b - Q2min - Q3min - Q4min - Q5min) > -0.001

Do While Application.Round(c, 1) <= Q2max And _
(Qsys - b - c - d - e - f) >= -0.001 Or _
(Qsys - Q1min - c - Q3min - Q4min - Q5min) > -0.001

Do While Application.Round(d, 1) <= Q3max And _
(Qsys - b - c - d - e - f) >= -0.001 Or _
(Qsys - Q1min - Q2min - d - Q4min - Q5min) > -0.001

Do While Application.Round(e, 1) <= Q4max And _
(Qsys - b - c - d - e - f) >= 0.001 Or _
(Qsys - Q1min - Q2min - Q3min - e - Q5min) > -0.001

Do While Application.Round(f, 1) <= Q5max And _
(Qsys - b - c - d - e - f) >= -0.001 Or _
(Qsys - Q1min - Q2min - Q3min - Q4min - f) > -0.001

If Abs(Qsys - b - c - d - e - f) < 0.001 Then
Cells(x, 1) = b
Cells(x, 2) = c
Cells(x, 3) = d
Cells(x, 4) = e
Cells(x, 5) = f

Cells(x, 7) = b + c + d + e + f
'Debug.Print x, b, c, d, e, f, b + c + d + e + f



x = x + 1

End If

f = f + 0.1
Loop
f = Q5min

e = e + 0.1
Loop
e = Q4min


d = d + 0.1
Loop
d = Q3min


c = c + 0.1
Loop
c = Q2min

b = b + 0.1
Loop
b = Q1min

End If

End Sub


--
Regards,
Tom Ogilvy

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