How to use if and elif on checking variables?

Answered

Han Shih

• September 22, 2019 20:50

Dear Python/Gurobi professionals:

Can you help meva question?

If I have two variable,  AA[I,J] and BB[I,J,K]   where I, J, K are index for demensions

How can I check if v.varName= AA[I,J] or v.varName=BB[I,J,K] so I can print as below?

for v in m.getVars():
   if v.varName = AA ???:

       print(AA"))
   elif v.varName = BB ???: 

       print("BB")

 

Thank you very much

Robert

0

• 

  Eli Towle

  Gurobi Staff

  • September 23, 2019 17:34

  Hi Robert,

  Assuming you want to look for variables whose names start with these letters, you can use the following:

  for v in m.getVars():
      if v.varName.startswith("AA"):
          print("AA")
      elif v.varName.startswith("BB"):
          print("BB")

  However, it's usually possible to avoid searching for variables by name. This can be done by creating a variable from the object returned by the addVar() or addVars() method. For example,

  aa = m.addVars(5, 5, name="AA")

  creates 25 variables with names AA[0,0], AA[0,1], ..., AA[4,4]. In this example, aa is a tupledict object that contains these variables. This object is very useful, because it allows you direct access to the set of "AA" variables:

  for v in aa:
      print(v.varName)

  Thus, the aa tupledict object can be used to build constraints, retrieve variable values, etc. I hope this helps!

  0
• 

  Han Shih

  • September 23, 2019 17:41

  

  

  

  Hi Eli,

  Thank you very much. It works!

  Best

  Robert

  0
• 

  Han Shih

  • September 25, 2019 16:10

  

  

  

  Hell Eli,

  Can you please help me another question?

  I have a code as below:

  for v in m.getVars():
       print('%s %g' % (v.varName, v.x))
  
  

  The varName is 3 by 2 dimension, so x is 3 by 2 dimension too

  When I print, its output is like the following

  A[1,1] 1
  A[1,2] 3
  A[2,1] 2
  A[2,2] 4
  A[3,1] 5
  A[3,2] 3

  is there any way to print a line for each row, like as below:?

  A[1,1] 1   A[1,2] 3
  A[2,1] 2   A[2,2] 4
  A[3,1] 5   A[3,2] 3

  Thank you very much

  Robert

   

   

   

   

   

   

  0
• 

  Eli Towle

  Gurobi Staff

  • September 25, 2019 22:53

  Hi Robert,

  Assuming your decision variables were added in the following manner:

  A = m.addVars(range(1,4), range(1,3), name="A")

  you can print a line for each row as follows:

  for i in range(1, 4):
      alist = ["%s %g" % (v.varName, v.X) for v in A.select(i, '*')]
      print("\t".join(alist))

  This code snippet uses the select() method of the tupledict object, as well as a Python list comprehension. An example of the output:

  A[1,1] 1        A[1,2] 3   
  A[2,1] 2        A[2,2] 4   
  A[3,1] 5        A[3,2] 3   

  I hope this helps!

  Eli

   

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• 

  Han Shih

  • September 26, 2019 00:35

  

  

  

  Hi Eli,

  Thank you very much for your help. It seems not easy to write the codes. I will give a try.

  Sincerely,

  Robert

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