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Use 0-indexing for variables removed via block_elimination #91

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Use 0-indexing for variables removed via block_elimination #91

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a62a0c7
allow variables for block_elimination to be 0-indexed
stevenan5 Mar 11, 2026
5c34833
change block_elimination signature
stevenan5 Mar 11, 2026
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13 changes: 7 additions & 6 deletions cython/pycddlib.pxi
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Original file line number Diff line number Diff line change
Expand Up @@ -89,14 +89,15 @@ cdef _get_set(set_type set_):
elem for elem in range(set_[0]) if set_member(elem + 1, set_)
}

cdef _set_set(set_type set_, elems):
cdef _set_set(set_type set_, elems, bool is_var_ind=False):
# set elements of set_type by elements from a Python Container
cdef unsigned long elem
offset = 2 if is_var_ind else 1
for elem in range(set_[0]):
if elem in elems:
set_addelem(set_, elem + 1)
set_addelem(set_, elem + offset)
else:
set_delelem(set_, elem + 1)
set_delelem(set_, elem + offset)

cdef setfam_from_ptr(dd_SetFamilyPtr dd_setfam):
# create Python Sequence[Set] from dd_SetFamilyPtr, and
Expand Down Expand Up @@ -1171,8 +1172,8 @@ def fourier_elimination(mat: Matrix) -> Matrix:
return matrix_from_ptr_with_error(dd_mat, error)


def block_elimination(mat: Matrix, col_set: Container[int]) -> Matrix:
"""Eliminate the variables *col_set* from the system of linear inequalities *mat*.
def block_elimination(mat: Matrix, var_set: Container[int]) -> Matrix:
"""Eliminate the variables *var_set* from the system of linear inequalities *mat*.
It does this by using the generators of the dual linear system,
where the generators are calculated using the double description algorithm.

Expand All @@ -1191,7 +1192,7 @@ def block_elimination(mat: Matrix, col_set: Container[int]) -> Matrix:
cdef dd_ErrorType error = dd_NoError
set_initialize(&dd_colset, mat.dd_mat.colsize)
try:
_set_set(dd_colset, col_set)
_set_set(dd_colset, var_set, True)
dd_mat = dd_BlockElimination(mat.dd_mat, dd_colset, &error)
return matrix_from_ptr_with_error(dd_mat, error)
finally:
Expand Down
6 changes: 3 additions & 3 deletions test/test_block_elimination.py
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ def test_block_elimination_1() -> None:
# 0 <= 1 + a + b + c + d, 0 <= 1 + 2a - b - c - d
array = [[1, 1, 1, 1, 1], [1, 2, -1, -1, -1]]
mat1 = cdd.matrix_from_array(array, rep_type=cdd.RepType.INEQUALITY)
mat2 = cdd.block_elimination(mat1, {2, 3, 4})
mat2 = cdd.block_elimination(mat1, {1, 2, 3})
# 0 <= 2 + 3a
assert_matrix_almost_equal(mat2.array, [[2, 3]])
assert mat2.lin_set == set()
Expand All @@ -23,7 +23,7 @@ def test_block_elimination_2() -> None:
]
mat1 = cdd.matrix_from_array(array, rep_type=cdd.RepType.INEQUALITY)
# eliminate last variable, same as fourier
mat2 = cdd.block_elimination(mat1, {3})
mat2 = cdd.block_elimination(mat1, {2})
assert_matrix_almost_equal(
mat2.array,
[
Expand All @@ -39,7 +39,7 @@ def test_block_elimination_3() -> None:
# 0 = -2 + x + y, 0 <= y
array = [[-2, 1, 1], [0, 0, 1]]
mat1 = cdd.matrix_from_array(array, rep_type=cdd.RepType.INEQUALITY, lin_set=[0])
mat2 = cdd.block_elimination(mat1, {2})
mat2 = cdd.block_elimination(mat1, {1})
# 0 <= 2 - x
assert_matrix_almost_equal(mat2.array, [[2, -1]])
assert mat2.lin_set == set()
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