Adding interface to the SCIP solver

src/pulp/solvers.py

@@ -99,12 +99,16 @@ def initialize(filename, operating_system='linux', arch='64'):
         pulp_cbc_path = config.get("locations", "PulpCbcPath")
     except configparser.Error:
         pulp_cbc_path = 'cbc'
+    try:
+        scip_path = config.get("locations", "ScipPath")
+    except configparser.Error:
+        scip_path = 'scip'
     for i,path in enumerate(coinMP_path):
         if not os.path.dirname(path):
             #if no pathname is supplied assume the file is in the same directory
             coinMP_path[i] = os.path.join(os.path.dirname(config_filename),path)
     return cplex_dll_path, ilm_cplex_license, ilm_cplex_license_signature,\
-        coinMP_path, gurobi_path, cbc_path, glpk_path, pulp_cbc_path
+        coinMP_path, gurobi_path, cbc_path, glpk_path, pulp_cbc_path, scip_path
 
 #pick up the correct config file depending on operating system
 PULPCFGFILE = "pulp.cfg"
@@ -134,8 +138,8 @@ else: #run as a script
     DIRNAME = os.path.dirname(fname)
     config_filename = os.path.join(DIRNAME,
                                    PULPCFGFILE)
-cplex_dll_path, ilm_cplex_license, ilm_cplex_license_signature, \
-        coinMP_path, gurobi_path, cbc_path, glpk_path, pulp_cbc_path = \
+cplex_dll_path, ilm_cplex_license, ilm_cplex_license_signature, coinMP_path,\
+        gurobi_path, cbc_path, glpk_path, pulp_cbc_path, scip_path = \
         initialize(config_filename, operating_system, arch)
 
 
@@ -429,12 +433,12 @@ GLPK = GLPK_CMD
 
 class CPLEX_CMD(LpSolver_CMD):
     """The CPLEX LP solver"""
-    
+
     def __init__(self, path = None, keepFiles = 0, mip = 1,
             msg = 0, options = [], timelimit = None):
         LpSolver_CMD.__init__(self, path, keepFiles, mip, msg, options)
         self.timelimit = timelimit
-    
+
     def defaultPath(self):
         return self.executableExtension("cplex")
 
@@ -2524,3 +2528,110 @@ class GurobiFormulation(object):
             else:
                 raise TypeError("Can only add LpConstraint, LpAffineExpression or True objects")
             return self
+
+class SCIP_CMD(LpSolver_CMD):
+    """The SCIP optimization solver"""
+
+    SCIP_STATUSES = {
+        'unknown': LpStatusUndefined,
+        'user interrupt': LpStatusNotSolved,
+        'node limit reached': LpStatusNotSolved,
+        'total node limit reached': LpStatusNotSolved,
+        'stall node limit reached': LpStatusNotSolved,
+        'time limit reached': LpStatusNotSolved,
+        'memory limit reached': LpStatusNotSolved,
+        'gap limit reached': LpStatusNotSolved,
+        'solution limit reached': LpStatusNotSolved,
+        'solution improvement limit reached': LpStatusNotSolved,
+        'restart limit reached': LpStatusNotSolved,
+        'optimal solution found': LpStatusOptimal,
+        'infeasible': LpStatusInfeasible,
+        'unbounded': LpStatusUnbounded,
+        'infeasible or unbounded': LpStatusNotSolved,
+    }
+
+    def defaultPath(self):
+        return self.executableExtension(scip_path)
+
+    def available(self):
+        """True if the solver is available"""
+        return self.executable(self.path)
+
+    def actualSolve(self, lp):
+        """Solve a well formulated lp problem"""
+        if not self.executable(self.path):
+            raise PulpSolverError("PuLP: cannot execute "+self.path)
+
+        # TODO: should we use tempfile instead?
+        if not self.keepFiles:
+            pid = os.getpid()
+            tmpLp = os.path.join(self.tmpDir, "%d-pulp.lp" % pid)
+            tmpSol = os.path.join(self.tmpDir, "%d-pulp.sol" % pid)
+        else:
+            tmpLp = lp.name+"-pulp.lp"
+            tmpSol = lp.name+"-pulp.sol"
+
+        lp.writeLP(tmpLp)
+        proc = [
+            'scip', '-c', 'read %s' % tmpLp, '-c', 'optimize',
+            '-c', 'write solution %s' % tmpSol, '-c', 'quit'
+        ]
+        proc.extend(self.options)
+        if not self.msg:
+            proc.append('-q')
+
+        self.solution_time = clock()
+        subprocess.check_call(proc, stdout=sys.stdout, stderr=sys.stderr)
+        self.solution_time += clock()
+
+        if not os.path.exists(tmpSol):
+            raise PulpSolverError("PuLP: Error while executing "+self.path)
+
+        lp.status, values = self.readsol(tmpSol)
+        lp.assignVarsVals(values)
+        if not self.keepFiles:
+            for f in (tmpLp, tmpSol):
+                try:
+                    os.remove(f)
+                except:
+                    pass
+
+        return lp.status
+
+    def readsol(self,filename):
+        """Read a SCIP solution file"""
+        with open(filename) as f:
+            # First line must containt 'solution status: <something>'
+            try:
+                line = f.readline()
+                comps = line.split(': ')
+                assert comps[0] == 'solution status'
+                assert len(comps) == 2
+            except:
+                raise
+                raise PulpSolverError("Can't read SCIP solver output: %r" % line)
+
+            status = SCIP_CMD.SCIP_STATUSES.get(comps[1].strip(), LpStatusUndefined)
+
+            # Look for an objective value. If we can't find one, stop.
+            try:
+                line = f.readline()
+                comps = line.split(': ')
+                assert comps[0] == 'objective value'
+                assert len(comps) == 2
+                float(comps[1].strip())
+            except:
+                raise PulpSolverError("Can't read SCIP solver output: %r" % line)
+
+            # Parse the variable values.
+            values = {}
+            for line in f:
+                try:
+                    comps = line.split()
+                    values[comps[0]] = float(comps[1])
+                except:
+                    raise PulpSolverError("Can't read SCIP solver output: %r" % line)
+
+        return status, values
+
+SCIP = SCIP_CMD