Speed up PowExpr._evaluate via the C-level API

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Replaced `format()` with f-strings in examples
 - Made expression fields read-only to prevent accidental runtime modification
 - Methods taking a list of variables (e.g. `addConsKnapsack()`) no longer convert it to a NumPy array to check its dimension
+- Speed up `PowExpr._evaluate` via the C-level API
 ### Removed
 
 ## 6.3.0 - 2026.10.11

src/pyscipopt/expr.pxi

@@ -58,6 +58,7 @@ from libc.math cimport cos as c_cos
 from libc.math cimport exp as c_exp
 from libc.math cimport fabs as c_fabs
 from libc.math cimport log as c_log
+from libc.math cimport pow as c_pow
 from libc.math cimport sqrt as c_sqrt
 from libc.math cimport sin as c_sin
 from libc.math cimport INFINITY
@@ -839,7 +840,11 @@ cdef class PowExpr(GenExpr):
         return f"**({self.children[0]},{self.expo})"
 
     cpdef double _evaluate(self, Solution sol) except *:
-        return (<GenExpr>self.children[0])._evaluate(sol) ** self.expo
+        cdef double base = (<GenExpr>self.children[0])._evaluate(sol)
+        cdef double expo = <double>self.expo
+        if base == 0.0 and expo < 0:
+            raise ZeroDivisionError("0.0 cannot be raised to a negative power")
+        return c_pow(base, expo)
 
     cdef PowExpr copy(self, bint copy=True):
         cdef PowExpr res = PowExpr.__new__(PowExpr)

tests/test_expr.py

@@ -257,6 +257,23 @@ def test_getVal_with_GenExpr():
     with pytest.raises(ValueError, match="math domain error"):
         m.getVal(sin(math.inf))
 
+
+def test_getVal_pow_negative_exponent():
+    m = Model()
+    x = m.addVar(lb=1, ub=1, name="x")
+    y = m.addVar(lb=2, ub=2, name="y")
+    z = m.addVar(lb=0, ub=0, name="z")
+    m.optimize()
+
+    # C-level pow with a negative exponent (matches Python: 2.0**-2.0 == 0.25)
+    assert 2.0 ** -2.0 == 0.25
+    assert m.getVal(x ** -2.0) == 1
+
+    # zero to a negative power raises, like Python's 0.0**-1.0;
+    # z / x would short-circuit to 0 in ProdExpr before evaluating x**-1, so divide by z
+    with pytest.raises(ZeroDivisionError):
+        m.getVal(y / z)
+
     with pytest.raises(ValueError, match="math domain error"):
         m.getVal(cos(-math.inf))