#!/bin/env python # # Construct a problem from scratch with variables of various # types. Adds indicator constraints, Special Ordered Sets (SOSs), and # shows how to retrieve such data once it has been added to the # problem using the API functions # from __future__ import print_function import xpress as xp N = 40 S = range (N) m = xp.problem ("test restriction") xp.controls.miprelstop = 0 # # All variables used in this example # v1 = xp.var (lb=0, ub=10, threshold=5, vartype=xp.continuous) v2 = xp.var (lb=1, ub=7, threshold=5, vartype=xp.continuous) v3 = xp.var (lb=5, ub=10, threshold=7, vartype=xp.semicontinuous) v4 = xp.var (lb=1, ub=7, threshold=3, vartype=xp.semiinteger) vb = xp.var (vartype = xp.integer, lb = 0, ub = 1) v = [xp.var (name = "y{0}".format (i), lb = 0, ub = 2*N) for i in S] # set name of a variable as cc = xp.constraint (body=v1 - v2, lb = 2, ub = 15) cc0 = xp.constraint (body=v1 + v2, lb = 2, ub = 15) m.addVariable (vb, v, v1, v2, v3, v4) # adds both v, a vector (list) of variables, and v1 and v2, two scalar variables. m.addConstraint (cc) # Indices of variables can be retrieved both using their name and # their Python object. print ("index of v[0] from name: ", m.getIndexFromName (2, "y0")) print ("index of v[0]: ", m.getIndex (v[0])) # Indicator constraints consist of a tuple with a condition on a # binary variable and a constraint) ind1 = (vb == 1, v1 + v2 >= 6) ind2 = (vb == 1, v1 + v3 >= 7) m.addIndicator (ind1) # adds the first indicator constraint m.addIndicator ((vb == 1, v1 + v3 <= 10), ind2) # adds another indicator constraint and the second one defined above s = xp.sos ([v1,v2],[2,4], name = "mynewsos", type=2) m.addSOS (s) # Showcases the use of getIndex() print ("get index: var v1 -->", m.getIndex (v1), "; con cc -->", m.getIndex (cc), "; sos -->", m.getIndex (s)) ii_inds = [] ii_comps = [] m.getindicators (ii_inds, ii_comps, 1, 3) print ("getind: ", ii_inds, ii_comps) print ("SOS:", s.name, s) # Objects such as SOSs, variables, constraints, etc. can be copied with the copy() method. sos2 = s.copy () m.setObjective (xp.Sum ([i*v[i] for i in S])) # objective overwritten at each setObjective () m.solve () # Retrieve a solution: first declare an empty string, then call the getmipsol() function to fill it up. mipsol = [] m.getmipsol (mipsol) s1 = m.getSolution (v1, v2, v [10:30]) # get a subset of the solutions s2 = m.getSolution (S) # can get it with indices as well print ("v1: ", m.getSolution (v1), ", v2: ", m.getSolution (v2), "; sol vector: ", m.getSolution (), "; obj: ", m.getObjVal (), sep="") # default separator between strings is " " # Adds yet another constraint to the problem and saves it, then removes an SOS and saves another version m.addConstraint ((1,25 * v1 - 2,5*v2 + 4,3) * (3,1 * v2 - 2 * v1 - 5,2) + 72,5 * v1**2 + 73 * v2**2 <= 1950) m.write ("restriction", "lp") m.delSOS (s) m.write ("restriction-noSOS", "lp") m.solve () # # We create another problem, but can continue to use the objects # created originally for the first problem. Note that the constraints # must have been defined here as otherwise a constraint obtained from # a previously read problem can't be added to another problem. # m2 = xp.problem (); cc2 = cc.copy () print ("name of copy:", cc2.name, ", orig:", cc.name) m2.addVariable (v1,v2) m2.addConstraint (cc2) m2.addConstraint (xp.Sum (2*v1) <= 100) m2.addConstraint (xp.Sum (44) <= 100) m2.addSOS (sos2) m2.addSOS (xp.sos ([1,v1],[2,4], name = "mynewsos2", type=2)) m2.write ("example3", "lp") m2.read ("example3.lp") # This is how you can retrieve a SOS using its index sss = m2.getSOS (0) print ("solution of the restricted problem: ", m.getSolution ())