Merge pull request #2971 from mathgeekcoder/highspy-scalar-division

Added support for scalar division to highspy

Author: jajhall

highs/highspy/highs.py

@@ -1701,6 +1701,15 @@ def __ge__(self, other: Union[float, int, highs_var, highs_linear_expression]):
         else:
             return highs_linear_expression(self).__ge__(other)
 
+    # self / scalar
+    def __truediv__(self, other: Union[float, int, highs_linear_expression]):
+        expr = highs_linear_expression(self)
+        expr /= other
+        return expr
+
+    # scalar / self
+    def __rtruediv__(self, other: Union[float, int, highs_linear_expression]):
+        raise Exception("Only division of a linear expression by a scalar is allowed.")
 
 # highs constraint
 class highs_cons(object):
@@ -2243,6 +2252,32 @@ def __isub__(self, other: Union[float, int, highs_var, highs_linear_expression])
 
             self.constant = (self.constant or 0.0) - float(other)
             return self
+        
+    # expr / scalar
+    def __truediv__(self, other: Union[float, int, highs_linear_expression]):
+        copy = highs_linear_expression(self)
+        copy /= other
+        return copy
+
+    # expr /= scalar
+    def __itruediv__(self, other: Union[float, int, highs_linear_expression]):
+        if isinstance(other, (float, int)):
+            divisor = float(other)
+
+        elif isinstance(other, highs_linear_expression) and other.idxs == [] and other.constant is not None:
+            divisor = float(other.constant)
+
+        else:
+            raise Exception("Only division by a scalar is allowed.")
+
+        if divisor == 0:
+            raise ZeroDivisionError("division by zero")
+
+        return self.__imul__(1.0 / divisor)
+
+    # scalar / expr
+    def __rtruediv__(self, other: Union[float, int, highs_var, highs_linear_expression]):
+        raise Exception("Only division of a linear expression by a scalar is allowed.")        
 
     def __imul__(self, other: Union[float, int, highs_var, highs_linear_expression]):
         if isinstance(other, (float, int)):

tests/test_highspy.py

@@ -2043,6 +2043,36 @@ def test_multiply(self):
         e1 *= x - 4 <= 3
         self.assertEqualExpr(e1, [x], [1], None, [-self.h.inf, 7])
 
+    def test_divide(self):
+        x, y = self.x[0:2]
+
+        expr = x / 4
+        self.assertEqualExpr(expr, [x], [0.25])
+
+        expr = (x + 2 * y + 8) / 4
+        self.assertEqualExpr(expr, [x, y], [0.25, 0.5], 2)
+
+        expr = (4 <= x + 2 * y <= 8) / 2
+        self.assertEqualExpr(expr, [x, y], [0.5, 1], None, [2, 4])
+
+        expr = (x + 2 * y) / highs_linear_expression(4)
+        self.assertEqualExpr(expr, [x, y], [0.25, 0.5])
+
+        expr = x + 2 * y + 8
+        expr /= 4
+        self.assertEqualExpr(expr, [x, y], [0.25, 0.5], 2)
+
+        expr = 4 <= x + 2 * y <= 8
+        expr /= -2
+        self.assertEqualExpr(expr, [x, y], [-0.5, -1], None, [-4, -2])
+
+        self.assertRaises(Exception, lambda: x / y)
+        self.assertRaises(Exception, lambda: (x + y) / (x + 1))
+        self.assertRaises(Exception, lambda: 2 / x)
+        self.assertRaises(Exception, lambda: 2 / (x + y))
+        self.assertRaises(ZeroDivisionError, lambda: x / 0)
+        self.assertRaises(ZeroDivisionError, lambda: (x + y) / highs_linear_expression(0))
+
     def test_simplify(self):
         x, y, z = self.x[0:3]