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__`, `SumExpr.__neg__`, `ProdExpr.__neg__` and `Constant.__neg__` via C-level API
 - Set `__array_priority__` for MatrixExpr and MatrixExprCons
 - changed addConsNode() and addConsLocal() to mirror addCons() and accept ExprCons instead of Constraint
 - Improved `chgReoptObjective()` performance

src/pyscipopt/expr.pxi

@@ -45,9 +45,10 @@
 import math
 from typing import TYPE_CHECKING
 
-from pyscipopt.scip cimport Variable, Solution
-from cpython.dict cimport PyDict_Next
+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
 
@@ -308,8 +309,15 @@ 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)
@@ -659,14 +667,31 @@ cdef class SumExpr(GenExpr):
         self.coefs = []
         self.children = []
         self._op = Operator.add
+
+    def __neg__(self) -> SumExpr:
+        cdef int i = 0, n = len(self.coefs)
+        cdef list coefs = [0.0] * n
+        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.__new__(SumExpr)
+        res.coefs = coefs
+        res.children = self.children.copy()
+        res.constant = -self.constant
+        res._op = Operator.add
+        return res
+
     def __repr__(self):
         return self._op + "(" + str(self.constant) + "," + ",".join(map(lambda child : child.__repr__(), self.children)) + ")"
 
     cpdef double _evaluate(self, Solution sol) except *:
         cdef double res = self.constant
         cdef int i = 0, n = len(self.children)
         cdef list children = self.children
-        cdef list coefs = self.coefs
+        cdef double[:] coefs = self.coefs
         for i in range(n):
             res += <double>coefs[i] * (<GenExpr>children[i])._evaluate(sol)
         return res
@@ -682,6 +707,13 @@ cdef class ProdExpr(GenExpr):
         self.children = []
         self._op = Operator.prod
 
+    def __neg__(self) -> ProdExpr:
+        cdef ProdExpr res = ProdExpr.__new__(ProdExpr)
+        res.constant = -res.constant
+        self.children = self.children.copy()
+        res._op = Operator.prod
+        return res
+
     def __repr__(self):
         return self._op + "(" + str(self.constant) + "," + ",".join(map(lambda child : child.__repr__(), self.children)) + ")"
 
@@ -746,11 +778,16 @@ cdef class UnaryExpr(GenExpr):
 
 # class for constant expressions
 cdef class Constant(GenExpr):
+
     cdef public number
+
     def __init__(self,number):
         self.number = number
         self._op = Operator.const
 
+    def __neg__(self):
+        return Constant(-self.number)
+
     def __repr__(self):
         return str(self.number)
 

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: ...

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 Constant, Expr, ExprCons, GenExpr, ProdExpr, SumExpr, Term
 
 
 @pytest.fixture(scope="module")
@@ -218,3 +218,33 @@ def test_getVal_with_GenExpr():
 
     with pytest.raises(ZeroDivisionError):
         m.getVal(1 / z)
+
+
+def test_neg():
+    m = Model()
+    x = m.addVar(name="x")
+
+    expr = (x + 1) ** 3
+    neg_expr = -expr
+    assert isinstance(expr, Expr)
+    assert isinstance(neg_expr, Expr)
+    assert (
+        str(neg_expr)
+        == "Expr({Term(x, x, x): -1.0, Term(x, x): -3.0, Term(x): -3.0, Term(): -1.0})"
+    )
+
+    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]
+
+    assert str(-Constant(3.0)) == "-3.0"