def time_frequency_cc_difference(t, s1, s2, dt_new, width, threshold):
"""
Straight port of tfa_cc_new.m
:param t: discrete time
:param s1: discrete signal 1
:param s2: discrete signal 2
:param dt_new: time increment in the tf domain
:param width: width of the Gaussian window
:param threshold: fraction of the absolute signal below which the Fourier
transform is set to zero in order to reduce computation time
"""
# New time axis
ti = utils.matlab_range(t[0], t[-1], dt_new)
# Interpolate both signals to the new time axis
si1 = interp1d(t, s1, kind=1)(ti)
si2 = interp1d(t, s2, kind=1)(ti)
# Extend the time axis, required for the correlation
N = len(ti)
t_cc = utils.matlab_range(t[0], (2 * N - 2) * dt_new, dt_new)
# Rename some variables
s1 = si1
s2 = si2
t_min = t_cc[0]
# Initialize the meshgrid
N = len(t_cc)
dnu = 1.0 / (N * dt_new)
nu = utils.matlab_range(0, float(N - 1) / (N * dt_new), dnu)
tau = t_cc
TAU, NU = np.meshgrid(tau, nu)
# Compute the time frequency representation
tfs = np.zeros(NU.shape, dtype="complex128")
for k in xrange(len(tau)):
# Window the signals
w = utils.gaussian_window(ti - tau[k], width)
f1 = w * s1
f2 = w * s2
if np.abs(f1).max() > (threshold * np.abs(s1).max()):
cc = utils.cross_correlation(f2, f1)
tfs[k, :] = np.fft.fft(cc) / np.sqrt(2.0 * np.pi) * dt_new
tfs[k, :] = tfs[k, :] * np.exp(-2.0 * np.pi * 1j * t_min * nu)
else:
tfs[k, :] = 0.0
return TAU, NU, tfs
def time_frequency_cc_difference(t, s1, s2, dt_new, width, threshold):
"""
Straight port of tfa_cc_new.m
:param t: discrete time
:param s1: discrete signal 1
:param s2: discrete signal 2
:param dt_new: time increment in the tf domain
:param width: width of the Gaussian window
:param threshold: fraction of the absolute signal below which the Fourier
transform is set to zero in order to reduce computation time
"""
# New time axis
ti = utils.matlab_range(t[0], t[-1], dt_new)
# Interpolate both signals to the new time axis
si1 = interp1d(t, s1, kind=1)(ti)
si2 = interp1d(t, s2, kind=1)(ti)
# Extend the time axis, required for the correlation
N = len(ti)
t_cc = utils.matlab_range(t[0], (2 * N - 2) * dt_new, dt_new)
# Rename some variables
s1 = si1
s2 = si2
t_min = t_cc[0]
# Initialize the meshgrid
N = len(t_cc)
dnu = 1.0 / (N * dt_new)
nu = utils.matlab_range(0, float(N - 1) / (N * dt_new), dnu)
tau = t_cc
TAU, NU = np.meshgrid(tau, nu)
# Compute the time frequency representation
tfs = np.zeros(NU.shape, dtype="complex128")
for k in xrange(len(tau)):
# Window the signals
w = utils.gaussian_window(ti - tau[k], width)
f1 = w * s1
f2 = w * s2
if np.abs(f1).max() > (threshold * np.abs(s1).max()):
cc = utils.cross_correlation(f2, f1)
tfs[k, :] = np.fft.fft(cc) / np.sqrt(2.0 * np.pi) * dt_new
tfs[k, :] = tfs[k, :] * np.exp(-2.0 * np.pi * 1j * t_min * nu)
else:
tfs[k, :] = 0.0
return TAU, NU, tfs
def test_cross_correlation():
"""
Tests the cross correlation function and compares it to a reference
solution calculated in Matlab.
"""
# Load the matlab file.
matlab_file = os.path.join(data_dir, "matlab_cross_correlation_reference_solution.mat")
cc_matlab = loadmat(matlab_file)["cc"][0]
# Calculate two test signals.
_, u = utils.get_dispersed_wavetrain()
_, u0 = utils.get_dispersed_wavetrain(a=3.91, b=0.87, c=0.8, body_wave_factor=0.015, body_wave_freq_scale=1.0 / 2.2)
cc = utils.cross_correlation(u, u0)
np.testing.assert_allclose(cc, cc_matlab)
def time_frequency_cc_difference(t, s1, s2, width, threshold=1E-2):
"""
Straight port of tfa_cc_new.m
:param t: discrete time
:param s1: discrete signal 1
:param s2: discrete signal 2
:param width: width of the Gaussian window
:param threshold: fraction of the absolute signal below which the Fourier
transform is set to zero in order to reduce computation time
"""
dt = t[1] - t[0]
# Extend the time axis, required for the correlation
N = len(t)
t_cc = np.linspace(t[0], t[0] + (2 * N - 2) * dt, (2 * N - 1))
N = len(t_cc)
dnu = 1.0 / (N * dt)
nu = np.linspace(0, (N - 1) * dnu, N)
tau = t_cc
cc_freqs = scipy.fftpack.fftfreq(len(t_cc), d=dt)
freqs = scipy.fftpack.fftfreq(len(t), d=dt)
# Compute the time frequency representation
tfs = np.zeros((len(t), len(t)), dtype="complex128")
threshold = np.abs(s1).max() * threshold
for k in range(len(t)):
# Window the signals
w = utils.gaussian_window(t - tau[k], width)
f1 = w * s1
f2 = w * s2
if min(np.abs(f1).max(), np.abs(f2).max()) < threshold:
continue
cc = utils.cross_correlation(f2, f1)
tfs[k, :] = \
scipy.interpolate.interp1d(cc_freqs, scipy.fftpack.fft(cc))(freqs)
tfs *= dt / np.sqrt(2.0 * np.pi)
return tau, nu, tfs
def time_frequency_cc_difference(t, s1, s2, width, threshold=1E-2):
"""
Straight port of tfa_cc_new.m
:param t: discrete time
:param s1: discrete signal 1
:param s2: discrete signal 2
:param width: width of the Gaussian window
:param threshold: fraction of the absolute signal below which the Fourier
transform is set to zero in order to reduce computation time
"""
dt = t[1] - t[0]
# Extend the time axis, required for the correlation
N = len(t)
t_cc = np.linspace(t[0], t[0] + (2 * N - 2) * dt, (2 * N - 1))
N = len(t_cc)
dnu = 1.0 / (N * dt)
nu = np.linspace(0, (N - 1) * dnu, N)
tau = t_cc
cc_freqs = scipy.fftpack.fftfreq(len(t_cc), d=dt)
freqs = scipy.fftpack.fftfreq(len(t), d=dt)
# Compute the time frequency representation
tfs = np.zeros((len(t), len(t)), dtype="complex128")
threshold = np.abs(s1).max() * threshold
for k in xrange(len(t)):
# Window the signals
w = utils.gaussian_window(t - tau[k], width)
f1 = w * s1
f2 = w * s2
if min(np.abs(f1).max(), np.abs(f2).max()) < threshold:
continue
cc = utils.cross_correlation(f2, f1)
tfs[k, :] = \
scipy.interpolate.interp1d(cc_freqs, scipy.fftpack.fft(cc))(freqs)
tfs *= dt / np.sqrt(2.0 * np.pi)
return tau, nu, tfs
def test_cross_correlation(self):
"""
Tests the cross correlation function and compares it to a reference
solution calculated in Matlab.
"""
# Load the matlab file.
matlab_file = os.path.join(
self.data_dir, "matlab_cross_correlation_reference_solution.mat")
cc_matlab = loadmat(matlab_file)["cc"][0]
# Calculate two test signals.
_, u = utils.get_dispersed_wavetrain()
_, u0 = utils.get_dispersed_wavetrain(a=3.91,
b=0.87,
c=0.8,
body_wave_factor=0.015,
body_wave_freq_scale=1.0 / 2.2)
cc = utils.cross_correlation(u, u0)
np.testing.assert_allclose(cc, cc_matlab)