Variable names in LP file format

CPLEX conforms to these rules about variable names in the LP file format.

Variables can be named anything in LP format provided that the name does not exceed 255 characters, all of which must be alphanumeric (a-z, A-Z, 0-9) or one of these symbols: ! " # $ % & ( ) , . ; ? @ _ ‘ ’ { } ~. Longer names are truncated to 255 characters. A variable name can not begin with a number or a period.

The letter E or e, alone or followed by other valid symbols, or followed by another E or e, should be avoided as this notation is reserved for exponential entries. Thus, variables can not be named e9, E-24, E8cats, or other names that could be interpreted as an exponent. Even variable names such as eels or example can cause a read error, depending on their placement in an input line.

Good Practice: Variable names begin with a letter (other than E or e) or with an underscore.

Multi-dimensional arrays of variables from OPL

LP format does not support the square brackets [ and ] in variable names. This convention imposes special considerations about multi-dimensional arrays in OPL.

When CPLEX translates your algebraic OPL model to the LP format, it must transform all multi-dimensional arrays of variables into scalar variables. This transformation assigns a different name to each element of each such array. In renaming the elements of arrays of variables, CPLEX does not simply concatenate the indices of an element to approximate a new multi-digit index because simply concatenating the indices of elements as they are does not rename the elements unambiguously. For example, consider a two-dimensional array named myarray with elements such as myarray[1][23] and myarray[12][3]. Simple concatenation produces one ambiguous name, myarray[123], for both of those distinct elements. Consequently, to avoid such ambiguity in renaming the elements of a multi-dimensional array of variables, the transformation to LP format introduces a separator (#). In this example, myarray[1][23] is renamed as myarray#1#23 and myarray[12][3] is renamed as myarray#12#3.

Conversion of names in LP files generated by CPLEX applications

A CPLEX application can create names of constraints and variables in a model, then export that model as an LP file. In such a case, the CPLEX application programming interface (API) routines that create the names of variables are not restricted by the LP format syntax specified in this topic. Consequently, an LP file exported by a CPLEX application can contain names of constraints or variables that violate the syntax of the LP format. CPLEX tries to avoid this situation by automatically converting names containing characters associated with arithmetic operations, such as '+', '-', '*', '^', and '['. CPLEX also automatically converts other characters that are ineligible for names (such as ":") to names that adhere to the syntax of LP format. CPLEX displays the following warning message when such a conversion occurs:

 
Warning:  Output names have been modified to conform to LP format.