Functions of GAMSCHK and Examples


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Ask for a display of a variable or equation and you recieve

----## VAR MAKECHAIR
## MAKECHAIR(PLANT2,FUNCTIONAL,NORMAL)

OBJT 15.000
RESOURCEQ(PLANT2,SMLLATHE) 0.80000
RESOURCEQ(PLANT2,LRGLATHE) 0.50000
TRNCHAIREQ(PLANT2,FUNCTIONAL) -1.0000
UPPER BOUND 5000.0
or
----## EQU LINKTABLE
## LINKTABLE(FANCY)
MAKETABLE(PLANT1,FANCY) -1.0000
TRANSPORT(PLANT3,TABLES,FANCY) -1.0000
SELL(PLANT1,DINSETS,FANCY) 1.0000
=L= 0.00000E+00

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Ask about the characteristics of selected variables and equations and you get




  Is Tot Pos Neg Nln Minimum Maximum
----### Requested Variables Non Cof Cof Cof Cof Absolute Absolute
SELL(PLANT1,TABLES, 0 2 1 1 0 1.000 1.000
FUNCTIONAL)
  Is Tot Pos Neg Nln Minimum Maximum
----### Requested Equations Non Cof Cof Cof Cof Absolute Absolute
RESOURCEQ(PLANT1,LABOR) 0 3 3 0 0 1.000 5.000


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Request a report of the characteristics of equation and variable blocks and you get

Variable Sign Numb Numb Pos Neg Non Maximum Minimum
Block Res Vars Nonl Coef Coef Coef Absolute Absolute
MAKECHAIR >=0 12 0 60 12 0 1.700 .2000
MAKETABLE >=0 6 0 16 4 0 5.000 1.000


Equation Type Numb Numb Pos Neg Non Pos Neg Maximum Minimum
Block Res Eqns Nonl Coef Coef Coef RHS RHS Absolute Absolute
OBJT =E= 1 0 23 10 0 0 0 1100. 5.000
RESOURCEQ =L= 12 0 60 0 0 11 0 5.000 .2000

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Examine a GAMS model to see whether any variables and equations contain specification errors and you get messages like the following

----### Analysis of Variables ( nonlinear terms at current point)

**** Warning These variables will equal zero because they have a zero lower bound an undesirable object function coefficient all 0 or - coefficients in the =G= rows all 0 or + coefficients in the =L= rows and no coefficients in the =E= rows

## MAKETABLE(PLANT2,FUNCTIONAL)
MAKETABLE(PLANT2,FANCY)

----### Analysis of Equations ( nonlinear terms at current point)

**** Warning This =L= constraint causes all variables in it to have a zero solution value since the nonnegative variables present have only 0 or + coefficients the nonpositive variables present have only 0 or - coefficients the unrestricted variables have only zero coefficients and the rhs is zero.

## RESOURCEQ(PLANT2,TOP)

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You can generate a schematic of the structure of the variable and equation blocks and you get something like

  | M M T   N |    
  | A A R   E |    
  | K K A   T |    
  | E E N   I |    
  | C T S   N |    
  | H A P S C |    
  | A B O E O |   R
  | I L R L M |   H
  | R E T L E |   S
OBJT | + + + - + | E 0
RESOURCEQ | + +       | L +
LINKTABLE |   - - +   | L 0
LINKCHAIR |     - +   | L 0
TRNCHAIREQ | -   + +   | L 0
TRNTABLEEQ |   - + +   | L 0  
Variable Typ | + + + + u      


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Ask for a block picture and you can examine the number of coeficients in the intersections of variable and equation blocks

  |           |     C #
  | M M T   N |     o  
  | A A R   E |     e o
  | K K A   T |     f f
  | E E N   I |     f  
  | C T S   N |        
  | H A P S C |     C E
  | A B O E O |   R n q
  | I L R L M |   H t n
  | R E T L E |   S s s
  | --- --- --- --- --- | --- --- --- ---
OBJT | 12+ 4+ 6+   1+ | E 0 23+ 1
  |       10-   |     10-
RESOURCEQ | 48+ 12+       | L 11+ 60+ 12
  |           |      
LINKTABLE |       4+   | L 0 4+ 2
  |   2- 2-     |       4-
LINKCHAIR |       2+   | L 0 2+ 2
  |     4-     |       4-
TRNCHAIREQ |     4+ 4+   | L 0 8+ 4
  | 12-         |       12-
TRNTABLEEQ |     2+ 2+   | L 0 4+ 2
  |   2-       |       2-
  | --- --- --- --- --- | --- --- --- ---
Coeff Cnts | 60+ 16+ 12+ 12+ 1+ |   11+ 101+
  | 12- 4- 6- 10-   |   32-
# of Vars | 12 6 6 10 1 |
Variable Typ | >=0 >=0 >=0 >=0 <0>


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Ask for a block picture and you can look at the scaling characteristics of the variable and equation blocks

    |           | R E
    | M M T   N | H q
    | A A R   E | S u
    | K K A   T |    
    | E E N   I | M M
    | C T S   N | a a
    | H A P S C | x x
    | A B O E O | M M
    | I L R L M | i i
    | R E T L E | n n
    | --- --- --- --- --- | --- ---
OBJT Max | 26.6 100 20 1100 1 | 0 1100
  Min | 15 80 5 82 1 | 0 1
RESOURCEQ Max | 1.7 5 0 0 0 | 210 5
  Min | 0.2 1 0 0 0 | 40 0.2
LINKTABLE Max | 0 1 1 1 0 | 0 1
  Min | 0 1 1 1 0 | 0 1
LINKCHAIR Max | 0 0 1 6 0 | 0 6
  Min | 0 0 1 4 0 | 0 1
TRNCHAIREQ Max | 1 0 1 1 0 | 0 1
  Min | 1 0 1 1 0 | 0 1
TRNTABLEEQ Max | 0 1 1 1 0 | 0 1
  Min | 0 1 1 1 0 | 0 1
    | --- --- --- --- --- | --- ---
Total Var Max | 26.6 100 20 1100 1 | 210
  Min | 0.2 1 1 1 1 | 40

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You can generate a schematic for small GAMS models or portions of larger models depicting the location of coefficients by sign and magnitude as follows

  |             R  
  | T T T T T T H  
  | R R R R R R S P   N
  | A A A A A A   O   E   R
  | N N N N N N C S   G   O
  | S S S S S S O I A A A W
  | P P P P P P E T I T I C
  | O O O O O O F I J I J N
  | R R R R R R F V   V   T
  | T T T T T T S E S E S S
  |  
  | 1 2 3 4 5 6
------------
OBJT 1 | D E E D D 6 = 0   11   1   12
LINKTABLE 1 |     3       <0   0   1   1
LINKTABLE 2 |       3     <0   0   1   1
LINKCHAIR 1 | 3       3   <0   0   2   2
LINKCHAIR 2 |   3       3 <0   0   2   2
TRNCHAIREQ 1 | C           <0   1       1
------------
LOWER BND | 0 0 0 0 0 0
UPPER BND | + + + + + +
------------
POSITIVE | 3 0 3 0 3 0
COLUMN CTS | 0 3 0 3 0 2
NEGATIVE | 1 0 1 0 1 0
COLUMN CTS | 0 1 0 1 0 2

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Ask to reconstruct the reduced costs after a model solution and you get

----### BUDGETING VARIABLES

----## VAR MAKECHAIR
## MAKECHAIR(PLANT2,FANCY,NORMAL)
SOLUTION VALUE 73.0195
UPPER BOUND 5000.00
EQN Aij Ui Aij*Ui
OBJT 25.000 1.0000 25.000
RESOURCEQ(PLANT2,SMLLATHE) 1.2000 47.770 57.324
RESOURCEQ(PLANT2,LRGLATHE) .70000 38.830 27.181
RESOURCEQ(PLANT2,LABOR) .80000 19.369 15.495
TRNCHAIREQ(PLANT2,FANCY) -1.0000 125.00 -125.00
TRUE REDUCED COST     .00000E+00


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Ask to reconstruct the activity within equations after a model solution and you get

----### ROW SUMMING EQUATIONS
----## EQU RESOURCEQ
## RESOURCEQ(PLANT2,SMLLATHE)
VAR Aij Xj Aij*Xj
MAKECHAIR(PLANT2,FUNCTIONAL, .80000 62.233 49.787
NORMAL)
MAKECHAIR(PLANT2,FANCY,NORMAL) 1.2000 73.020 87.623
MAKECHAIR(PLANT2,FANCY,MAXLRG) .50000 5.1798 2.5899
=L=     =L=
RHS COEFF     140.00
 
SLACK EQUALS     .00000E+00
SHADOW PRICE     47.770


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Ask the program to find variables or equations which could be causing unbounded or infeasible models and you get

----### THESE VARIABLES ARE POTENTIALLY UNBOUNDED

To find the cause of unboundedness bound them or the objective function variable at a large value. Then solve and manually or through GAMSCHK find large levels for variables in solution

SELL(PLANT1,TABLES,FUNCTIONAL)


----### THESE EQUATIONS ARE POTENTIALLY INFEASIBLE

RESOUREQ(PLANT1,LABOR)

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