From 085d9191e633742e7617ff36564ca8e54124c251 Mon Sep 17 00:00:00 2001
From: Dimos Tsouros <dimosts988@gmail.com>
Date: Thu, 3 Oct 2024 14:36:33 +0200
Subject: [PATCH] cover cp.abs() using the builtin (#513)

* cover cp.abs() using the builtin

* abs implementation

* actually abs for only 1 element

* tests for builtins

* support vectorized

* recursive for iterable

* fix error in test for all_diff_except_n

* add testcase

* add testcase

* fix missing 'not'
remove redundant 'abs' code

* still overwrite __abs__ in expressions

* Update python_builtins.py

bit more explicit...

---------

Co-authored-by: wout4 <wout.vanroose@gmail.com>
Co-authored-by: Tias Guns <tias@ulyssis.org>
---
 cpmpy/expressions/__init__.py        |  2 +-
 cpmpy/expressions/python_builtins.py | 27 ++++++++++++++--
 tests/test_builtins.py               | 47 ++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 4 deletions(-)
 create mode 100644 tests/test_builtins.py

diff --git a/cpmpy/expressions/__init__.py b/cpmpy/expressions/__init__.py
index e86de9032..b695ff926 100644
--- a/cpmpy/expressions/__init__.py
+++ b/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
diff --git a/cpmpy/expressions/python_builtins.py b/cpmpy/expressions/python_builtins.py
index 7fcaa805c..140669a09 100644
--- a/cpmpy/expressions/python_builtins.py
+++ b/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)
+
+    
diff --git a/tests/test_builtins.py b/tests/test_builtins.py
new file mode 100644
index 000000000..5c95b13aa
--- /dev/null
+++ b/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')
\ No newline at end of file