Merge 7889ce5 into 1f3b13a

flipy/solvers/cbc_solver.py

@@ -2,6 +2,7 @@
 import tempfile
 import platform
 import subprocess
+from typing import Optional
 
 from flipy.lp_problem import LpProblem
 from flipy.solvers.base_solver import SolutionStatus
@@ -30,9 +31,22 @@ class CBCSolver:
         ('Windows', '64bit'): 'bin/cbc-win64/cbc.exe',
     }
 
-    def __init__(self) -> None:
-        """ Initialize the solver """
+    def __init__(self, mip_gap: float = 0.1, timeout: Optional[int] = None) -> None:
+        """ Initialize the solver
+
+        Parameters
+        ----------
+        mip_gap: float
+            Relative MIP optimality gap.
+            The solver will terminate (with an optimal result) when the gap between the lower and upper objective bound
+            is less than MIPGap times the absolute value of the upper bound
+            This can save some time if all you want to do is find a heuristic solution.
+        timeout: int
+            The time allowed for solving in seconds
+        """
         self.bin_path = os.getenv('CBC_SOLVER_BIN', self._find_cbc_binary())
+        self.mip_gap = mip_gap
+        self.timeout = timeout
 
     @classmethod
     def _find_cbc_binary(cls) -> str:
@@ -87,7 +101,7 @@ def solve(self, lp_problem: LpProblem) -> SolutionStatus:
         self.call_cbc(f.name, solution_file_path)
 
         if not os.path.exists(solution_file_path):
-            raise SolverError("Error while trying to solve the problem")
+            return SolutionStatus.NotSolved
 
         return self.read_solution(solution_file_path, lp_problem)
 
@@ -107,7 +121,14 @@ def call_cbc(self, lp_file_path: str, solution_file_path: str):
             Where to record the solution
         """
         pipe = open(os.devnull, 'w')
-        args = [self.bin_path, lp_file_path, 'branch', 'printingOptions', 'all', 'solution', solution_file_path]
+
+        args = [self.bin_path, lp_file_path]
+        if self.timeout:
+            args.extend(['sec', str(self.timeout)])
+        if self.mip_gap:
+            args.extend(['ratio', str(self.mip_gap)])
+        args.extend(['branch', 'printingOptions', 'all', 'solution', solution_file_path])
+
         coin_proc = subprocess.Popen(args, stderr=pipe, stdout=pipe)
         if coin_proc.wait() != 0:
             raise SolverError(f"Error while trying to execute {self.bin_path}")

tests/test_solvers/test_cbc_solver.py

@@ -0,0 +1,49 @@
+import mock
+
+import pytest
+
+from flipy import CBCSolver
+
+
+@pytest.fixture
+def cbc_solver():
+    return CBCSolver()
+
+
+class TestCBCSolver:
+
+    def test_init(self):
+        solver = CBCSolver()
+        assert solver.mip_gap == 0.1
+        assert solver.timeout is None
+
+    @mock.patch('platform.system')
+    @mock.patch('platform.architecture')
+    @pytest.mark.parametrize('system, arch, bin_path', [
+        ('Linux', '64bit', 'cbc-linux64'),
+        ('Linux', '64bit', 'bin/cbc-linux64/cbc'),
+        ('Darwin', '64bit', 'bin/cbc-osx/cbc'),
+        ('Windows', '32bit', 'bin/cbc-win32/cbc.exe'),
+        ('Windows', '64bit', 'bin/cbc-win64/cbc.exe'),
+    ])
+    def test_find_binary(self, mock_arch, mock_system, system, arch, bin_path, cbc_solver):
+        mock_arch.return_value = arch, None
+        mock_system.return_value = system
+        assert bin_path in cbc_solver._find_cbc_binary()
+
+    @mock.patch('platform.system')
+    @mock.patch('platform.architecture')
+    def test_unknown_sys(self, mock_arch, mock_system, cbc_solver):
+        mock_system.return_value = 'Plan9'
+        mock_arch.return_value = '32bit', None
+        with pytest.raises(Exception) as e:
+            cbc_solver._find_cbc_binary()
+        assert str(
+            e.value
+        ) == "no CBC solver found for system Plan9 32bit, please set the solver path manually with " \
+             "environment variable 'CBC_SOLVER_BIN'"
+
+    def test_find_custom_binary(self, monkeypatch, cbc_solver):
+        monkeypatch.setenv('CBC_SOLVER_BIN', '/my_custom_cbc_binary')
+        assert cbc_solver._find_cbc_binary() == '/my_custom_cbc_binary'
+