cover cp.abs() using the builtin

cpmpy/expressions/__init__.py

@@ -28,4 +28,4 @@
 from .globalconstraints import alldifferent, allequal, circuit # Old, to be deprecated
 from .globalfunctions import Maximum, Minimum, Abs, Element, Count, NValue, NValueExcept, Among
 from .core import BoolVal
-from .python_builtins import all, any, max, min, sum
+from .python_builtins import all, any, max, min, sum, abs

cpmpy/expressions/python_builtins.py

@@ -17,13 +17,15 @@
         max
         min
         sum
+        abs
 """
 import builtins  # to use the original Python-builtins
 
-from .utils import is_false_cst, is_true_cst
-from .variables import NDVarArray
+from .utils import is_false_cst, is_true_cst, is_any_list
+from .variables import NDVarArray, cpm_array
 from .core import Expression, Operator
-from .globalfunctions import Minimum, Maximum
+from .globalfunctions import Minimum, Maximum, Abs
+from ..exceptions import CPMpyException
 
 
 # Overwriting all/any python built-ins
@@ -125,3 +127,22 @@ def sum(*iterable, **kwargs):
 
     assert len(kwargs)==0, "sum over decision variables does not support keyword arguments"
     return Operator("sum", iterable)
+
+
+def abs(element):
+    """
+        abs() overwrites the python built-in to support decision variables.
+
+        if the element given is not a CPMpy expression, the built-in is called
+        else an Absolute functional global constraint is constructed.
+    """
+    if is_any_list(element):  # compat: not allowed by builtins.abs(), but allowed by numpy.abs()
+        return cpm_array([abs(elem) for elem in element])
+
+    if isinstance(element, Expression):
+        # create global
+        return Abs(element)
+
+    return builtins.abs(element)
+
+

tests/test_builtins.py

@@ -0,0 +1,47 @@
+import unittest
+
+import cpmpy as cp
+from cpmpy.exceptions import CPMpyException
+
+iv = cp.intvar(-8, 8, shape=5)
+
+
+class TestBuiltin(unittest.TestCase):
+
+    def test_max(self):
+        constraints = [cp.max(iv) + 9 <= 8]
+        model = cp.Model(constraints)
+        self.assertTrue(model.solve())
+        self.assertTrue(cp.max(iv.value()) <= -1)
+
+        model = cp.Model(cp.max(iv).decompose_comparison('!=', 4))
+        self.assertTrue(model.solve())
+        self.assertNotEqual(str(cp.max(iv.value())), '4')
+
+    def test_min(self):
+        constraints = [cp.min(iv) + 9 == 8]
+        model = cp.Model(constraints)
+        self.assertTrue(model.solve())
+        self.assertEqual(str(cp.min(iv.value())), '-1')
+
+        model = cp.Model(cp.min(iv).decompose_comparison('==', 4))
+        self.assertTrue(model.solve())
+        self.assertEqual(str(cp.min(iv.value())), '4')
+
+    def test_abs(self):
+        constraints = [cp.abs(iv[0]) + 9 <= 8]
+        model = cp.Model(constraints)
+        self.assertFalse(model.solve())
+
+        #with list
+        constraints = [cp.abs(iv+2) <= 8, iv < 0]
+        model = cp.Model(constraints)
+        self.assertTrue(model.solve())
+
+        constraints = [cp.abs([iv[0], iv[2], iv[1], -8]) <= 8, iv < 0]
+        model = cp.Model(constraints)
+        self.assertTrue(model.solve())
+
+        model = cp.Model(cp.abs(iv[0]).decompose_comparison('!=', 4))
+        self.assertTrue(model.solve())
+        self.assertNotEqual(str(cp.abs(iv[0].value())), '4')

tests/test_globalconstraints.py

@@ -116,7 +116,7 @@ def test_alldifferent_except_n(self):
 
         # and some more
         iv = cp.intvar(-8, 8, shape=3)
-        self.assertTrue(cp.Model([cp.AllDifferentExceptN(iv,2)]).solve())
+        self.assertTrue(cp.Model([cp.AllDifferentExceptN(iv,4)]).solve())
         self.assertTrue(cp.AllDifferentExceptN(iv,4).value())
         self.assertTrue(cp.Model([cp.AllDifferentExceptN(iv,7), iv == [7, 7, 1]]).solve())
         self.assertTrue(cp.AllDifferentExceptN(iv,7).value())