Let
X1 = 1, if GPU RX580 is to be bought, otherwise X1 = 0
X2 = 1, if GPU RX590 is to be bought, otherwise X2 = 0
X3 = 1, if GPU Vega 56 is to be bought, otherwise X3 = 0
X4 = 1, if GPU Vega 64 is to be bought, otherwise X4 = 0
X5 = 1, if GPU Radeon VII is to be bought, otherwise X5 = 0
N1 = number of GPU RX580 to be bought
N2 = number of GPU RX590 to be bought
N3 = number of GPU Vega 56 to be bought
N4 = number of GPU Vega 64 to be bought
N5 = number of GPU Radeon VII to be bought
Q1) Linear program is following:
Max 3859N1+4450N2+6604N3+7864N4+3360N5
s.t.
X1+X2+X3+X4+X5<=4
180N1+210N2+300N3+400N4+650N5 <= 1500
10X1-N1 >= 0, (here, 10 is just a
hypothetical large number, larger than the maximum possible value
of Ni)
10X2-N2 >= 0
10X3-N3 >= 0
10X4-N4 >= 0
10X5-N5 >= 0
Xi binary,
Ni >= 0
Solution using LINGO is following:

N1 = 0
N2 = 0
N3 = 5
N4 = 0
N5 = 0
|
GPU |
RX580 |
RX590 |
Vega 56 |
Vega 64 |
Radeon VII |
|
Count |
0 |
0 |
5 |
0 |
0 |
Q2)
Revised model and solution is following:

N1 = 1
N2 = 1
N3 = 2
N4 = 0
N5 = 0
|
GPU |
RX580 |
RX590 |
Vega 56 |
Vega 64 |
Radeon VII |
|
Count |
1 |
1 |
2 |
0 |
0 |
Q3) The revised model and solution is following:
Unit Cost is multiplied with 0.75 to account for 25% off on
price

|
GPU |
RX580 |
RX590 |
Vega 56 |
Vega 64 |
Radeon VII |
|
Count |
0 |
2 |
3 |
0 |
0 |
Q4)
Additional constraint for RAM space is added to the model.
Revised model and its solution is following:

|
GPU |
RX580 |
RX590 |
Vega 56 |
Vega 64 |
Radeon VII |
|
Count |
1 |
1 |
2 |
0 |
0 |
Lingo 170-Solution Report . Lingo! File Edit Solver Window Help Solution Report-Lingo1 Lindo Model- Lingo1 Global optimal solution found Max 3859N1+4450N2+6604N3+7864N4+3360N5 Objective value: 33020.00 Objective bound: 33020.00 Infeasibilities: 0.000000 S.t Extended solver steps: Total solver iterations: Elapsed runtime seconds: 0.40 180N1+210N2+300N3+400N4+650N5 1500 <= Model Class: MILP 10 Total variables: 1022-N2 0 >= Nonlinear variables: Integer variables: 10X3-N3-0 Total constraintS: 10X4-N4 -0 Nonlinear constraints: 25 Total nonzeros: Nonlinear nonzeros: END INT X1 Value INT X Variable Reduced Cost INT X3 N1 0.000000 103.4000 INT X4 N2 0.000000 172.8000 INT X5 N3 5.000000 0.000000 N4 0.000000 941.3333 N5 0.000000 10948.67 Xi 0.000000 0.000000 X2 0.000000 0.000000 X3 1.000000 0.000000 X4 0.000000 0.000000 x5 0.000000 0.000000 Row Slack or Surplus 33020.00 Dual Price 1.000000 1 3.000000 0.000000 0.000000 22.01333 0.000000 0.000000 For Help, press F1 CAP NUM
Lingo 17.0-Solution Report-Lingo! File Edit Solver Window Help Solution Report-Lingo1 Lindo Model-Lingo Global optimal solution found Max 3859N1+4450N2+6604N3+7864N4+336ONS Objective value: Objective bound: 21517.00 21517.00 Infeasibilities: 0.000000 s.t. Extended solver steps: X1 +X2+X3+X4+X5<-4 Total solver iterations: Elapsed runtime seconds: 0.15 180N1+210N2 +300N3+400N4+650N5 1000 <= Model Class: PILP 10X1-N0 10 Total variables: 10X2-N2 0 Nonlinear variables: >= Integer variables: 10 Total constraints: 10X4-N4 0 Nonlinear constraints: >= Total nonzeros: 25 Nonlinear nonzeros: END INT X1 | Variable INT X2 Value Reduced Cost INT X3 Ni 1.000000 -3859.000 INT X4 N2 1 . 000000 -4450.000 INT X5 N3 2.000000 -6604.000 GIN NI N4 0.000000 -7864.000 GIN N2 NS 0.000000 -3360.000 GIN N3 x1 1.000000 0.000000 GIN N4 1.000000 0.000000 X2 GIN NS X3 1.000000 0.000000 X4 0.000000 0.000000 X5 0.000000 0.000000 Row Slack or Surplus Dual Price 21517.00 1.000000 1.000000 0.000000 10.00000 0.000000 9.000000 0.000000 For Help, press F1 CAP NUM
翌Lingo 17.0-Solution Report-Lingo! File Edit Solver Window Help | [ | s, | F Solution Report . Lingo! Lindo Model-Lingo Global optimal solution found Objective value: Max 3859N14450N2+6604N3+7864N4+3360NS 28712.00 Objective bound: 28712.00 Infeasibilities: 0.000000 Extended solver steps: X1+X2+X3+X4+X5<-4 Total solver iterations: Elapsed runtime seconds: 0.12 135N1157.5N2+225N3+300N4+487.5N5 <-1000 Model Class: PILP Total variables: 10 10X2-X2 0 Nonlinear variables: >= 10 Integer variables: 10X3-N30 Total constraints: 10X4-X4 0 Nonlinear constraints: >= 25 10X5-NS0 Total nonzeros: Nonlinear nonzeros: END INT X1 Variable INT X2 Reduced Cost Value INT X3 N1 0.000000 -3859.000 INT X4 N2 2.000000 -4450.000 INT X5 N3 3.000000 -6604.000 GIN N1 N4 0.000000 -7864.000 GIN N2 N5 0.000000 -3360.000 GIN N3 0.000000 0.000000 X1 GIN N4 X2 1 . 000000 0.000000 GIN N5 X3 1.000000 0.000000 X4 0.000000 0.000000 X5 1.000000 0.000000 Row Slack or Surplus 28712.00 Dual Price 1.000000 1.000000 0.000000 10.00000 0.000000 0.000000 0.000000 For Help, press F1 NUM
翌Lingo 17.0-Solution Report-Lingo! Eile Edit Solver Window Help -11回11 x 'solution Report-Lingo! Lindo Model Lingo1 Global optimal solution found Objective value: Objective bound: Max 3859N1+4450N2+6604N3+7864N4+3360N5 21517.00 21517.00 Infeasibilities: 0.000000 S.t Extended solver steps: X1+X2+X3+X4+X5- Total solver iterations: 0.14 Elapsed runtime seconds: 180N1+210N2+300N3+400N4+65ONS 1000 Model Class: PILP 8N1+8N2+8N3+8N4+16N5 32 <= Total variables: 10 10X1-N0 Nonlinear variables: Integer variables: 10 10X2-N20 Total constraints: 10X3-N3-0 Nonlinear constraints: 0 Total nonzeros: 30 Nonlinear nonzeros: 0 10X5-NS0 END Value Variable Reduced Cost INT X1 N1 1.000000 -3859.000 INT X2 N2 1.000000 4450.000 -6604.000 N3 2.000000 INT X3 INT X4 N4 0.000000 7864.000 -3360.000 INT X5 NS 0.000000 GIN N X1 1.000000 0.000000 GIN N2 X2 1.000000 0.000000 GIN N3 X3 1 . 000 000 0.000000 GIN N4 0.000000 0.000000 GIN N 0.000000 X5 0.000000 Row Slack or Surplus 21517.00 Dual Price 1 1.000000 1.000000 0.000000 10.00000 0.000000 0.000000 0.000000 For Help, press F1 CAP NUM