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- import numpy as np
- from numpy.testing import assert_allclose, assert_array_equal
- from pytest import raises as assert_raises
- from numpy.fft import fft, ifft
- from scipy.signal import max_len_seq
- class TestMLS:
- def test_mls_inputs(self):
- # can't all be zero state
- assert_raises(ValueError, max_len_seq,
- 10, state=np.zeros(10))
- # wrong size state
- assert_raises(ValueError, max_len_seq, 10,
- state=np.ones(3))
- # wrong length
- assert_raises(ValueError, max_len_seq, 10, length=-1)
- assert_array_equal(max_len_seq(10, length=0)[0], [])
- # unknown taps
- assert_raises(ValueError, max_len_seq, 64)
- # bad taps
- assert_raises(ValueError, max_len_seq, 10, taps=[-1, 1])
- def test_mls_output(self):
- # define some alternate working taps
- alt_taps = {2: [1], 3: [2], 4: [3], 5: [4, 3, 2], 6: [5, 4, 1], 7: [4],
- 8: [7, 5, 3]}
- # assume the other bit levels work, too slow to test higher orders...
- for nbits in range(2, 8):
- for state in [None, np.round(np.random.rand(nbits))]:
- for taps in [None, alt_taps[nbits]]:
- if state is not None and np.all(state == 0):
- state[0] = 1 # they can't all be zero
- orig_m = max_len_seq(nbits, state=state,
- taps=taps)[0]
- m = 2. * orig_m - 1. # convert to +/- 1 representation
- # First, make sure we got all 1's or -1
- err_msg = "mls had non binary terms"
- assert_array_equal(np.abs(m), np.ones_like(m),
- err_msg=err_msg)
- # Test via circular cross-correlation, which is just mult.
- # in the frequency domain with one signal conjugated
- tester = np.real(ifft(fft(m) * np.conj(fft(m))))
- out_len = 2**nbits - 1
- # impulse amplitude == test_len
- err_msg = "mls impulse has incorrect value"
- assert_allclose(tester[0], out_len, err_msg=err_msg)
- # steady-state is -1
- err_msg = "mls steady-state has incorrect value"
- assert_allclose(tester[1:], np.full(out_len - 1, -1),
- err_msg=err_msg)
- # let's do the split thing using a couple options
- for n in (1, 2**(nbits - 1)):
- m1, s1 = max_len_seq(nbits, state=state, taps=taps,
- length=n)
- m2, s2 = max_len_seq(nbits, state=s1, taps=taps,
- length=1)
- m3, s3 = max_len_seq(nbits, state=s2, taps=taps,
- length=out_len - n - 1)
- new_m = np.concatenate((m1, m2, m3))
- assert_array_equal(orig_m, new_m)
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