纸浆中的线性整数优化

Question

I was trying to do the following simple example optimization problem before starting a bigger problem. The code:

from pulp import *
x = LpVariable("x", 0, 3)
y = LpVariable("y", 0, 1)
prob = LpProblem("myProblem", LpMinimize)

prob += x + y <= 2
#objective function
prob += -4*x + y

status = prob.solve(GLPK(msg = 0))
#results
value(x)

I am getting the following error:

Traceback (most recent call last):
  File "C:\Users\mahabubalam\Desktop\Works\GUI\whiskas.py", line 85, in <module>
    status = prob.solve(GLPK(msg = 0))
  File "C:\Python34\lib\site-packages\pulp-1.5.6-py3.4.egg\pulp\pulp.py", line 1619, in solve
    status = solver.actualSolve(self, **kwargs)
  File "C:\Python34\lib\site-packages\pulp-1.5.6-py3.4.egg\pulp\solvers.py", line 335, in actualSolve
    raise PulpSolverError("PuLP: cannot execute "+self.path)
pulp.solvers.PulpSolverError: PuLP: cannot execute glpsol.exe

Can anyone please help me to understand why is that?

Answer 1

I have successfully run your code after doing the following two steps:

1. Download GLPK from

   http://sourceforge.net/projects/winglpk/files/latest/download (as mentioned by oyvind)

2. Unzip it into (for example) : C:\\glpk_is_here\\

3. Add GLPK binaries to your system path before running python C:\\>

4. , use python/ipython to run your code:
   C:\\>

5. See the results Out[4]: 2.0

Good luck.

Answer 2

I got this error when I used illegal characters in the name of the variables. From what I can gather in pulp's code (LpElement, to be exact), the characters -+[] ->/ are not allowed and are all replaced by an underscore.

Since discovering the error, I preprocess my variable names with the following function, fixing the issue:

  def variableName(s):
    # illegalChars = "-+[] ->/"
    s = s.replace("-","(hyphen)")
    s = s.replace("+","(plus)")
    s = s.replace("[","(leftBracket)")
    s = s.replace("]","(rightBracket)")
    s = s.replace(" ","(space)")
    s = s.replace(">","(greaterThan)")
    s = s.replace("/","(slash)")
    return s

Answer 3

This works for me in unbuntu:

   sudo apt-get install python-glpk  
   sudo apt-get install glpk-utils

I think in windows there is a similar solution

Answer 4

安装GLPK，例如从sourceforge.net/projects/winglpk安装

Answer 5

For Mac -- brew install glpk on terminal.

Homebrew is the best.