Generating block file for MILPBlock application using Python in DIP

MILPBlock is a prototype for a generic black-box solver for block-diagonal mixed integer linear programming problems that fully automates the branch-and-price-and-cut algorithm without additional user input. The user only needs to provide the mps file of the problem and the block file which indicates how many blocks in the model, which rows in each block etc.

Sometimes it is tedious to write the block file for the large scale problem. So we always expect to create the block file by the script language, which is easy and fast. Python is the right choice.

Here is an example showing the bin packing problem for using Python to create block file.

The objective function and the constraints are described using AMPL language as below :

param numItems;
param Capacity;

set Items = 1 .. numItems;
set Bins  = 1 .. (numItems+1);

param Weight{Items};

var x{i in Items, j in Bins } binary ;

# minimize the number of bins

minimize num_Of_Bins : sum{i in Items} x[i,numItems+1];

subject to condition1 {i in Items}: sum{j in 1 .. numItems}x[i,j] = 1 ;

subject to condition2 {j in Items, i in Items}: x[i,j]<=x[j,numItems+1] ;

subject to condition3 {j in Items}: sum{i in Items}x[i,j]*Weight[i] <=Capacity*\
x[j,numItems+1];


Suppose we have 50 items, and 50 blocks, each block has 51 rows corresponding to j.

The python code to create a block file of the ' list ' format is shown below

*************************************************************************
f = open('test.block','w')
for i in range(50):
    f.write(str(i))
    f.write(' ')
    f.write(str(51))
    f.write('\n')
    for j in range(50):
    f.write(str(50+50*i+j))
    f.write(' ')
    f.write(str(2550+i))
    f.write('\n')

f.close()
*************************************************************************