[Help-glpk] Ruby LP Solver issues - "row name too long" for more than 29 items

[Lukas Meyer]

Dear all,

I created a model to solve a linear programming capital budgeting problem with Ruby (OPL):

Maximize NPV of projects (x1…x5) by taking into account Budget and Resource constraints (c1, c2). Solution can only be 0 or 1.
 

Example:
Maximize: 928 x1 + 908 x2 + 801 x3 + 543 x4 + 944 x5
Constraints:
c1: 398 x1 + 151 x2 + 129 x3 + 275 x4 + 291 x5 <= 800
c2: 111 x1 + 139 x2 + 56 x3 + 54 x4 + 123 x5 <= 200
Result is binary (0 or 1): x1 x2 x3 x4 x5

My code works correctly until a certain number of projects (maximum 29). If I use more than 29 Projects (x1 + x2 + .. + x30) the code crashes with the following result:

glp_set_row_name: i = 1; row name too long

Error detected in file glpapi01.c at line 441

Abort trap: 6

Since I would like to process a lot more in order to solve the problem I need to somehow change my setup. I can’t really imagine that this is a given maximum. 

Does anybody have encountered a similar problem and could point me into the right direction? 

Many thanks and best regards,

Lukas