If you inadvertently make an error entering problem data, the problem object will not correspond to your intentions. One possible result may be a segmentation fault or other disruption of your application. In other cases, ILOG CPLEX may solve a different model from the one you intended, and that situation may or may not result in error messages from ILOG CPLEX.

To help you detect this kind of error, you can set the parameter CPX_PARAM_DATACHECK to the value CPX_ON to activate additional checking of array arguments for CPXcopy...(), CPXread...(), and CPXchg...() functions. The additional checks include:

• invalid sense/ctype/sostype values

• indexes out of range, for example, rowind >= numrows

• duplicate entries

• matbeg or sosbeg array with decreasing values

• NANs in double arrays

• NULLs in name arrays

When the parameter is set to CPX_OFF, only simple checks, for example checking for the existence of the environment, are performed.

ILOG CPLEX also provides diagnostic routines to look for common errors in the definition of problem data. In the standard distribution of ILOG CPLEX, the file check.c contains the source code for these routines:

• CPXcheckcopylp()

• CPXcheckcopylpwnames()

• CPXcheckcopyqpsep()

• CPXcheckcopyquad()

• CPXcheckaddrows()

• CPXcheckaddcols()

• CPXcheckchgcoeflist()

• CPXcheckvals()

• CPXcheckcopyctype()

• CPXcheckcopysos()

• CPXNETcheckcopynet()

Each of those routines performs a series of diagnostic tests of the problem data and issues warnings or error messages whenever it detects a potential error. To use them, you must compile and link the file check.c. After compiling and linking that file, you will be able to step through the source code of these routines with a debugger to help isolate problems.

If you have observed anomalies in your application, you can exploit this diagnostic capability by calling the appropriate routines just before a copying routine. The diagnostic routine may then detect errors in the problem data that could subsequently cause inexplicable behavior.

Those checking routines send all messages to one of the standard ILOG CPLEX message channels. You capture that output by setting the parameter CPX_PARAM_SCRIND (if you want messages directed to your screen) or by calling the routine CPXsetlogfile().