Functions of GAMSCHK and Examples – Bruce McCarl

Source: https://agecoresearch.tamu.edu/mccarl/gams-related-information/functions-of-gamschk-and-examples/ Parent: https://agecoresearch.tamu.edu/mccarl/

• Display the structure of user selected equations and/or variables example
• List the characteristics of selected groups of variables and equations example
• List the characteristics of equation and variable blocks example
• Examine a GAMS model to see whether any variables and equations contain specification errors example
• Generate a schematic of the structure of the variable and equation blocks example
• Examine the number of coeficients in the intersections of variable and equation blocks example
• Look at the scaling characteristics of the variable and equation blocks example
• Generate a schematic for small GAMS models or portions of larger models depicting the location of coefficients by sign and magnitude example
• Reconstruct the reduced cost of variables after a model solution example
• Reconstruct the activity within equations after a model solution example
• Find variables or equations which could be causing unbounded or infeasible models example

\ Top of Document\

Ask for a display of a variable or equation and you receive\ \ —-## VAR MAKECHAIR\

MAKECHAIR(PLANT2,FUNCTIONAL,NORMAL)

Top of Document\ \ Ask about the characteristics of selected variables and equations and you get\ \ \

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

Top of Document\ \ 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)\ \

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

Top of Document\ \ Ask for a block picture and you can examine the number of coefficients in the intersections of variable and equation blocks

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

Top of Document\ \ 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

Top of Document\ \ Ask to reconstruct the reduced costs after a model solution and you get\ \

Top of Document\ \ Ask to reconstruct the activity within equations after a model solution and you get\ \

Top of Document\ \ 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)\ \ Top of Document\