"""Compute the determinant of an polynomial array."""
from __future__ import annotations
import numpy
import numpoly
from ..baseclass import ndpoly, PolyLike
from ..dispatch import implements
[docs]@implements(numpy.linalg.det)
def det(a: PolyLike) -> ndpoly:
"""
Compute the determinant of an polynomial array.
Args:
a:
Input array to compute determinants for.
Shape on form `(..., M, M)`.
Return:
Determinant of `a`. Shape `(...)`.
Note:
Broadcasting rules apply, see the `numpy.linalg` documentation for
details.
Example:
>>> q0, q1 = numpoly.variable(2)
>>> a = numpoly.polynomial([[[1, 2], [3, 4]], [[1, q0], [q1, 1]]])
>>> numpoly.det(a)
polynomial([-2, -q0*q1+1])
"""
a = numpoly.aspolynomial(a)
assert a.ndim >= 2, a
assert a.shape[-2] == a.shape[-1], a.shape
dims = a.shape[-1]
index = (slice(None),) * (a.ndim - 2)
if dims == 2:
return (
a[index + (0, 0)] * a[index + (1, 1)]
- a[index + (1, 0)] * a[index + (0, 1)]
)
out = numpoly.zeros_like(a, shape=a.shape[:-2])
r = numpy.arange(1, dims, dtype=int)
for idx in range(dims):
idx0 = index + (0, idx)
idx1 = index + (slice(1, None), (r + idx) % dims)
out = out + a[idx0] * det(a[idx1])
return out