test and changelog

Author: Joao-Dionisio

CHANGELOG.md

@@ -3,7 +3,7 @@
 ## Unreleased
 ### Added
 ### Fixed
-- all fundamental callbacks now raise an error if not implemented
+- getTermsQuadratic() now correctly returns all linear terms
 ### Changed
 ### Removed
 

src/pyscipopt/scip.pxi

@@ -8090,18 +8090,6 @@ cdef class Model:
         """
         Retrieve bilinear, quadratic, and linear terms of a quadratic constraint.
 
-        According to SCIP's quadratic expression interface, a quadratic
-        expression is represented as
-
-            $x^T Q x + b^T x + c^T y + d$,
-
-        where variables in $x$ appear in the quadratic part (matrix $Q$) and
-        variables in $y$ appear only linearly.  The coefficients for $c^T y$
-        (purely linear part) are returned as ``linterms``.  For variables that
-        appear in the quadratic part (the $x$ variables), their associated
-        linear coefficients $b$ are stored together with the quadratic term
-        and are returned as part of ``quadterms``.
-
         Parameters
         ----------
         cons : Constraint
@@ -8117,9 +8105,8 @@ cdef class Model:
             coefficient ``lincoef`` associated with the same variable when it
             also appears linearly in the quadratic part.
         linterms : list of tuple
-            Pairs ``(var, coef)`` for variables that appear only in the pure
-            linear part (the ``c^T y`` term above), i.e., variables that do
-            not participate in any quadratic or bilinear term.
+            Pairs ``(var, coef)`` for variables that appear only in the pure, i.e.,
+            variables that do not participate in any quadratic or bilinear term.
 
         """
         cdef SCIP_EXPR* expr

tests/test_nonlinear.py

@@ -288,6 +288,56 @@ def test_quad_coeffs():
     assert linterms[0][0].name == z.name
     assert linterms[0][1] == 4
 
+
+def test_quad_coeffs_mixed_linear_and_quadratic():
+    """ensure getTermsQuadratic exposes all linear coefficients
+
+    ``linterms`` contains purely linear variables (those that do not appear
+    in the quadratic part).  For variables that also appear quadratically,
+    their linear coefficients are stored in the ``lincoef`` component of
+    ``quadterms``.
+    """
+    scip = Model()
+
+    var1 = scip.addVar(name="var1", vtype='C', lb=None)
+    var2 = scip.addVar(name="var2", vtype='C')
+    var3 = scip.addVar(name="var3", vtype='B')
+    var4 = scip.addVar(name="var4", vtype='B')
+
+    cons = scip.addCons(
+        8 * var4
+        + 4 * var3
+        - 5 * var2
+        + 6 * var3 ** 2
+        - 3 * var1 ** 2
+        + 2 * var2 * var1
+        + 7 * var1 * var3
+        == -2
+    )
+
+    bilinterms, quadterms, linterms = scip.getTermsQuadratic(cons)
+
+    # Linear part: getTermsQuadratic must report all linear coefficients,
+    # including those of variables that also appear quadratically or
+    # bilinearly.
+    lin_only = {v.name: c for (v, c) in linterms}
+    assert lin_only["var4"] == 8
+    assert lin_only["var3"] == 4
+    assert lin_only["var2"] == -5
+
+    # For completeness, checking if the coefficients from reconstructing the full linear
+    # coefficients from both linterms and quadterms match
+    full_lin = {}
+    for v, c in linterms:
+        full_lin[v.name] = full_lin.get(v.name, 0.0) + c
+    for v, _, lincoef in quadterms:
+        if lincoef != 0.0:
+            full_lin[v.name] = full_lin.get(v.name, 0.0) + lincoef
+
+    assert full_lin["var4"] == 8
+    assert full_lin["var3"] == 4
+    assert full_lin["var2"] == -5
+
 def test_addExprNonLinear():
     m = Model()
     x = m.addVar("x", lb=0, ub=1, obj=10)