Speed up -SumExpr, -ProdExpr and -Constant

CHANGELOG.md

@@ -23,6 +23,7 @@
 - Speed up MatrixExpr.add.reduce via quicksum
 - Speed up np.ndarray(..., dtype=np.float64) @ MatrixExpr
 - MatrixExpr and MatrixExprCons use `__array_ufunc__` protocol to control all numpy.ufunc inputs and outputs
+- Speed up `Expr.__neg__` and `ProdExpr.__neg__` and `Constant.__neg__` via C-level API
 ### Removed
 
 ## 6.0.0 - 2025.xx.yy

src/pyscipopt/expr.pxi

@@ -45,9 +45,11 @@
 import math
 from typing import TYPE_CHECKING
 
-from pyscipopt.scip cimport Variable, Solution
-from cpython.dict cimport PyDict_Next
+from cpython.array cimport array, clone
+from cpython.dict cimport PyDict_Next, PyDict_SetItem
+from cpython.object cimport Py_TYPE
 from cpython.ref cimport PyObject
+from pyscipopt.scip cimport Variable, Solution
 
 import numpy as np
 
@@ -56,6 +58,9 @@ if TYPE_CHECKING:
     double = float
 
 
+cdef array DOUBLE_TEMPLATE = array("d")
+
+
 def _is_number(e):
     try:
         f = float(e)
@@ -308,8 +313,15 @@ cdef class Expr:
         else:
             raise TypeError(f"Unsupported base type {type(other)} for exponentiation.")
 
-    def __neg__(self):
-        return Expr({v:-c for v,c in self.terms.items()})
+    def __neg__(self) -> Expr:
+        cdef dict res = {}
+        cdef Py_ssize_t pos = <Py_ssize_t>0
+        cdef PyObject* key_ptr
+        cdef PyObject* val_ptr
+
+        while PyDict_Next(self.terms, &pos, &key_ptr, &val_ptr):
+            PyDict_SetItem(res, <Term>key_ptr, -<double>(<object>val_ptr))
+        return Expr(res)
 
     def __sub__(self, other):
         return self + (-other)
@@ -647,6 +659,21 @@ cdef class GenExpr:
         '''returns operator of GenExpr'''
         return self._op
 
+    cdef GenExpr copy(self, bool copy = True):
+        cdef object cls = <type>Py_TYPE(self)
+        cdef GenExpr res = cls.__new__(cls)
+        res._op = self._op
+        res.children = self.children.copy() if copy else self.children
+        if cls is SumExpr:
+            self = <SumExpr>self
+            res = <SumExpr>res
+            res.constant = self.constant
+            res.coefs = clone(self.coefs, len(self.coefs), False) if copy else self.coefs
+        if cls is ProdExpr:
+            (<ProdExpr>res).constant = (<ProdExpr>self).constant
+        elif cls is PowExpr:
+            (<PowExpr>res).expo = (<PowExpr>self).expo
+        return res
 
 # Sum Expressions
 cdef class SumExpr(GenExpr):
@@ -656,9 +683,24 @@ cdef class SumExpr(GenExpr):
 
     def __init__(self):
         self.constant = 0.0
-        self.coefs = []
+        self.coefs = array("d")
         self.children = []
         self._op = Operator.add
+
+    def __neg__(self) -> SumExpr:
+        cdef int i = 0, n = len(self.coefs)
+        cdef array coefs = clone(DOUBLE_TEMPLATE, n, False)
+        cdef double[:] dest_view = coefs
+        cdef double[:] src_view = self.coefs
+
+        for i in range(n):
+            dest_view[i] = -src_view[i]
+
+        cdef SumExpr res = <SumExpr>self.copy()
+        res.constant = -res.constant
+        res.coefs = coefs
+        return res
+
     def __repr__(self):
         return self._op + "(" + str(self.constant) + "," + ",".join(map(lambda child : child.__repr__(), self.children)) + ")"
 
@@ -682,6 +724,11 @@ cdef class ProdExpr(GenExpr):
         self.children = []
         self._op = Operator.prod
 
+    def __neg__(self) -> ProdExpr:
+        cdef ProdExpr res = <ProdExpr>self.copy()
+        res.constant = -res.constant
+        return res
+
     def __repr__(self):
         return self._op + "(" + str(self.constant) + "," + ",".join(map(lambda child : child.__repr__(), self.children)) + ")"
 

src/pyscipopt/scip.pyi

@@ -343,7 +343,7 @@ class Expr:
     def __lt__(self, other: object) -> bool: ...
     def __mul__(self, other: Incomplete) -> Incomplete: ...
     def __ne__(self, other: object) -> bool: ...
-    def __neg__(self) -> Incomplete: ...
+    def __neg__(self) -> Expr: ...
     def __pow__(self, other: Incomplete, modulo: Incomplete = ...) -> Incomplete: ...
     def __radd__(self, other: Incomplete) -> Incomplete: ...
     def __rmul__(self, other: Incomplete) -> Incomplete: ...
@@ -386,7 +386,7 @@ class GenExpr:
     def __lt__(self, other: object) -> bool: ...
     def __mul__(self, other: Incomplete) -> Incomplete: ...
     def __ne__(self, other: object) -> bool: ...
-    def __neg__(self) -> Incomplete: ...
+    def __neg__(self) -> GenExpr: ...
     def __pow__(self, other: Incomplete, modulo: Incomplete = ...) -> Incomplete: ...
     def __radd__(self, other: Incomplete) -> Incomplete: ...
     def __rmul__(self, other: Incomplete) -> Incomplete: ...
@@ -2162,7 +2162,6 @@ class Term:
     def __lt__(self, other: object) -> bool: ...
     def __ne__(self, other: object) -> bool: ...
 
-@disjoint_base
 class UnaryExpr(GenExpr):
     def __init__(self, *args: Incomplete, **kwargs: Incomplete) -> None: ...
 

tests/test_expr.py

@@ -2,8 +2,8 @@
 
 import pytest
 
-from pyscipopt import Model, sqrt, log, exp, sin, cos
-from pyscipopt.scip import Expr, GenExpr, ExprCons, Term
+from pyscipopt import Model, cos, exp, log, sin, sqrt
+from pyscipopt.scip import Expr, ExprCons, GenExpr, ProdExpr, SumExpr, Term
 
 
 @pytest.fixture(scope="module")
@@ -218,3 +218,22 @@ def test_getVal_with_GenExpr():
 
     with pytest.raises(ZeroDivisionError):
         m.getVal(1 / z)
+
+
+def test_neg():
+    m = Model()
+    x = m.addVar(name="x")
+    base = sqrt(x)
+
+    expr = base * -1
+    neg_expr = -expr
+    assert isinstance(expr, ProdExpr)
+    assert isinstance(neg_expr, ProdExpr)
+    assert str(neg_expr) == "prod(1.0,sqrt(sum(0.0,prod(1.0,x))))"
+
+    expr = base + x - 1
+    neg_expr = -expr
+    assert isinstance(expr, SumExpr)
+    assert isinstance(neg_expr, SumExpr)
+    assert str(neg_expr) == "sum(1.0,sqrt(sum(0.0,prod(1.0,x))),prod(1.0,x))"
+    assert list(neg_expr.coefs) == [-1, -1]