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from sympy import S, I, ask, Q, Abs, simplify, exp, sqrt
from sympy.core.symbol import symbols
from sympy.matrices.expressions.fourier import DFT, IDFT
from sympy.matrices import det, Matrix, Identity
from sympy.testing.pytest import raises


def test_dft_creation():
    assert DFT(2)
    assert DFT(0)
    raises(ValueError, lambda: DFT(-1))
    raises(ValueError, lambda: DFT(2.0))
    raises(ValueError, lambda: DFT(2 + 1j))

    n = symbols('n')
    assert DFT(n)
    n = symbols('n', integer=False)
    raises(ValueError, lambda: DFT(n))
    n = symbols('n', negative=True)
    raises(ValueError, lambda: DFT(n))


def test_dft():
    n, i, j = symbols('n i j')
    assert DFT(4).shape == (4, 4)
    assert ask(Q.unitary(DFT(4)))
    assert Abs(simplify(det(Matrix(DFT(4))))) == 1
    assert DFT(n)*IDFT(n) == Identity(n)
    assert DFT(n)[i, j] == exp(-2*S.Pi*I/n)**(i*j) / sqrt(n)