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# Author: Travis Oliphant
# 2003
#
# Feb. 2010: Updated by Warren Weckesser:
# Rewrote much of chirp()
# Added sweep_poly()
from __future__ import division, print_function, absolute_import
from numpy import asarray, zeros, place, nan, mod, pi, extract, log, sqrt, \
exp, cos, sin, polyval, polyint
__all__ = ['sawtooth', 'square', 'gausspulse', 'chirp', 'sweep_poly']
def sawtooth(t, width=1):
"""
Return a periodic sawtooth or triangle waveform.
The sawtooth waveform has a period ``2*pi``, rises from -1 to 1 on the
interval 0 to ``width*2*pi``, then drops from 1 to -1 on the interval
``width*2*pi`` to ``2*pi``. `width` must be in the interval [0, 1].
Note that this is not band-limited. It produces an infinite number
of harmonics, which are aliased back and forth across the frequency
spectrum.
Parameters
----------
t : array_like
Time.
width : array_like, optional
Width of the rising ramp as a proportion of the total cycle.
Default is 1, producing a rising ramp, while 0 produces a falling
ramp. `t` = 0.5 produces a triangle wave.
If an array, must be the same length as t, causes wave shape to change
over time.
Returns
-------
y : ndarray
Output array containing the sawtooth waveform.
Examples
--------
A 5 Hz waveform sampled at 500 Hz for 1 second:
>>> from scipy import signal
>>> import matplotlib.pyplot as plt
>>> t = np.linspace(0, 1, 500)
>>> plt.plot(t, signal.sawtooth(2 * np.pi * 5 * t))
"""
t, w = asarray(t), asarray(width)
w = asarray(w + (t - t))
t = asarray(t + (w - w))
if t.dtype.char in ['fFdD']:
ytype = t.dtype.char
else:
ytype = 'd'
y = zeros(t.shape, ytype)
# width must be between 0 and 1 inclusive
mask1 = (w > 1) | (w < 0)
place(y, mask1, nan)
# take t modulo 2*pi
tmod = mod(t, 2 * pi)
# on the interval 0 to width*2*pi function is
# tmod / (pi*w) - 1
mask2 = (1 - mask1) & (tmod < w * 2 * pi)
tsub = extract(mask2, tmod)
wsub = extract(mask2, w)
place(y, mask2, tsub / (pi * wsub) - 1)
# on the interval width*2*pi to 2*pi function is
# (pi*(w+1)-tmod) / (pi*(1-w))
mask3 = (1 - mask1) & (1 - mask2)
tsub = extract(mask3, tmod)
wsub = extract(mask3, w)
place(y, mask3, (pi * (wsub + 1) - tsub) / (pi * (1 - wsub)))
return y
def square(t, duty=0.5):
"""
Return a periodic square-wave waveform.
The square wave has a period ``2*pi``, has value +1 from 0 to
``2*pi*duty`` and -1 from ``2*pi*duty`` to ``2*pi``. `duty` must be in
the interval [0,1].
Note that this is not band-limited. It produces an infinite number
of harmonics, which are aliased back and forth across the frequency
spectrum.
Parameters
----------
t : array_like
The input time array.
duty : array_like, optional
Duty cycle. Default is 0.5 (50% duty cycle).
If an array, must be the same length as t, causes wave shape to change
over time.
Returns
-------
y : ndarray
Output array containing the square waveform.
Examples
--------
A 5 Hz waveform sampled at 500 Hz for 1 second:
>>> from scipy import signal
>>> import matplotlib.pyplot as plt
>>> t = np.linspace(0, 1, 500, endpoint=False)
>>> plt.plot(t, signal.square(2 * np.pi * 5 * t))
>>> plt.ylim(-2, 2)
A pulse-width modulated sine wave:
>>> sig = np.sin(2 * np.pi * t)
>>> pwm = signal.square(2 * np.pi * 30 * t, duty=(sig + 1)/2)
>>> plt.subplot(2, 1, 1)
>>> plt.plot(t, sig)
>>> plt.subplot(2, 1, 2)
>>> plt.plot(t, pwm)
>>> plt.ylim(-1.5, 1.5)
"""
t, w = asarray(t), asarray(duty)
w = asarray(w + (t - t))
t = asarray(t + (w - w))
if t.dtype.char in ['fFdD']:
ytype = t.dtype.char
else:
ytype = 'd'
y = zeros(t.shape, ytype)
# width must be between 0 and 1 inclusive
mask1 = (w > 1) | (w < 0)
place(y, mask1, nan)
# on the interval 0 to duty*2*pi function is 1
tmod = mod(t, 2 * pi)
mask2 = (1 - mask1) & (tmod < w * 2 * pi)
place(y, mask2, 1)
# on the interval duty*2*pi to 2*pi function is
# (pi*(w+1)-tmod) / (pi*(1-w))
mask3 = (1 - mask1) & (1 - mask2)
place(y, mask3, -1)
return y
def gausspulse(t, fc=1000, bw=0.5, bwr=-6, tpr=-60, retquad=False,
retenv=False):
"""
Return a Gaussian modulated sinusoid:
``exp(-a t^2) exp(1j*2*pi*fc*t).``
If `retquad` is True, then return the real and imaginary parts
(in-phase and quadrature).
If `retenv` is True, then return the envelope (unmodulated signal).
Otherwise, return the real part of the modulated sinusoid.
Parameters
----------
t : ndarray or the string 'cutoff'
Input array.
fc : int, optional
Center frequency (Hz). Default is 1000.
bw : float, optional
Fractional bandwidth in frequency domain of pulse (Hz).
Default is 0.5.
bwr : float, optional
Reference level at which fractional bandwidth is calculated (dB).
Default is -6.
tpr : float, optional
If `t` is 'cutoff', then the function returns the cutoff
time for when the pulse amplitude falls below `tpr` (in dB).
Default is -60.
retquad : bool, optional
If True, return the quadrature (imaginary) as well as the real part
of the signal. Default is False.
retenv : bool, optional
If True, return the envelope of the signal. Default is False.
Returns
-------
yI : ndarray
Real part of signal. Always returned.
yQ : ndarray
Imaginary part of signal. Only returned if `retquad` is True.
yenv : ndarray
Envelope of signal. Only returned if `retenv` is True.
See Also
--------
scipy.signal.morlet
Examples
--------
Plot real component, imaginary component, and envelope for a 5 Hz pulse,
sampled at 100 Hz for 2 seconds:
>>> from scipy import signal
>>> import matplotlib.pyplot as plt
>>> t = np.linspace(-1, 1, 2 * 100, endpoint=False)
>>> i, q, e = signal.gausspulse(t, fc=5, retquad=True, retenv=True)
>>> plt.plot(t, i, t, q, t, e, '--')
"""
if fc < 0:
raise ValueError("Center frequency (fc=%.2f) must be >=0." % fc)
if bw <= 0:
raise ValueError("Fractional bandwidth (bw=%.2f) must be > 0." % bw)
if bwr >= 0:
raise ValueError("Reference level for bandwidth (bwr=%.2f) must "
"be < 0 dB" % bwr)
# exp(-a t^2) <-> sqrt(pi/a) exp(-pi^2/a * f^2) = g(f)
ref = pow(10.0, bwr / 20.0)
# fdel = fc*bw/2: g(fdel) = ref --- solve this for a
#
# pi^2/a * fc^2 * bw^2 /4=-log(ref)
a = -(pi * fc * bw) ** 2 / (4.0 * log(ref))
if t == 'cutoff': # compute cut_off point
# Solve exp(-a tc**2) = tref for tc
# tc = sqrt(-log(tref) / a) where tref = 10^(tpr/20)
if tpr >= 0:
raise ValueError("Reference level for time cutoff must be < 0 dB")
tref = pow(10.0, tpr / 20.0)
return sqrt(-log(tref) / a)
yenv = exp(-a * t * t)
yI = yenv * cos(2 * pi * fc * t)
yQ = yenv * sin(2 * pi * fc * t)
if not retquad and not retenv:
return yI
if not retquad and retenv:
return yI, yenv
if retquad and not retenv:
return yI, yQ
if retquad and retenv:
return yI, yQ, yenv
def chirp(t, f0, t1, f1, method='linear', phi=0, vertex_zero=True):
"""Frequency-swept cosine generator.
In the following, 'Hz' should be interpreted as 'cycles per time unit';
there is no assumption here that the time unit is one second. The
important distinction is that the units of rotation are cycles, not
radians.
Parameters
----------
t : ndarray
Times at which to evaluate the waveform.
f0 : float
Frequency (in Hz) at time t=0.
t1 : float
Time at which `f1` is specified.
f1 : float
Frequency (in Hz) of the waveform at time `t1`.
method : {'linear', 'quadratic', 'logarithmic', 'hyperbolic'}, optional
Kind of frequency sweep. If not given, `linear` is assumed. See
Notes below for more details.
phi : float, optional
Phase offset, in degrees. Default is 0.
vertex_zero : bool, optional
This parameter is only used when `method` is 'quadratic'.
It determines whether the vertex of the parabola that is the graph
of the frequency is at t=0 or t=t1.
Returns
-------
y : ndarray
A numpy array containing the signal evaluated at `t` with the
requested time-varying frequency. More precisely, the function
returns ``cos(phase + (pi/180)*phi)`` where `phase` is the integral
(from 0 to `t`) of ``2*pi*f(t)``. ``f(t)`` is defined below.
See Also
--------
sweep_poly
Notes
-----
There are four options for the `method`. The following formulas give
the instantaneous frequency (in Hz) of the signal generated by
`chirp()`. For convenience, the shorter names shown below may also be
used.
linear, lin, li:
``f(t) = f0 + (f1 - f0) * t / t1``
quadratic, quad, q:
The graph of the frequency f(t) is a parabola through (0, f0) and
(t1, f1). By default, the vertex of the parabola is at (0, f0).
If `vertex_zero` is False, then the vertex is at (t1, f1). The
formula is:
if vertex_zero is True:
``f(t) = f0 + (f1 - f0) * t**2 / t1**2``
else:
``f(t) = f1 - (f1 - f0) * (t1 - t)**2 / t1**2``
To use a more general quadratic function, or an arbitrary
polynomial, use the function `scipy.signal.waveforms.sweep_poly`.
logarithmic, log, lo:
``f(t) = f0 * (f1/f0)**(t/t1)``
f0 and f1 must be nonzero and have the same sign.
This signal is also known as a geometric or exponential chirp.
hyperbolic, hyp:
``f(t) = f0*f1*t1 / ((f0 - f1)*t + f1*t1)``
f1 must be positive, and f0 must be greater than f1.
"""
# 'phase' is computed in _chirp_phase, to make testing easier.
phase = _chirp_phase(t, f0, t1, f1, method, vertex_zero)
# Convert phi to radians.
phi *= pi / 180
return cos(phase + phi)
def _chirp_phase(t, f0, t1, f1, method='linear', vertex_zero=True):
"""
Calculate the phase used by chirp_phase to generate its output.
See `chirp_phase` for a description of the arguments.
"""
f0 = float(f0)
t1 = float(t1)
f1 = float(f1)
if method in ['linear', 'lin', 'li']:
beta = (f1 - f0) / t1
phase = 2 * pi * (f0 * t + 0.5 * beta * t * t)
elif method in ['quadratic', 'quad', 'q']:
beta = (f1 - f0) / (t1 ** 2)
if vertex_zero:
phase = 2 * pi * (f0 * t + beta * t ** 3 / 3)
else:
phase = 2 * pi * (f1 * t + beta * ((t1 - t) ** 3 - t1 ** 3) / 3)
elif method in ['logarithmic', 'log', 'lo']:
if f0 * f1 <= 0.0:
raise ValueError("For a geometric chirp, f0 and f1 must be "
"nonzero and have the same sign.")
if f0 == f1:
phase = 2 * pi * f0 * t
else:
beta = t1 / log(f1 / f0)
phase = 2 * pi * beta * f0 * (pow(f1 / f0, t / t1) - 1.0)
elif method in ['hyperbolic', 'hyp']:
if f1 <= 0.0 or f0 <= f1:
raise ValueError("hyperbolic chirp requires f0 > f1 > 0.0.")
c = f1 * t1
df = f0 - f1
phase = 2 * pi * (f0 * c / df) * log((df * t + c) / c)
else:
raise ValueError("method must be 'linear', 'quadratic', 'logarithmic',"
" or 'hyperbolic', but a value of %r was given." % method)
return phase
def sweep_poly(t, poly, phi=0):
"""
Frequency-swept cosine generator, with a time-dependent frequency.
This function generates a sinusoidal function whose instantaneous
frequency varies with time. The frequency at time `t` is given by
the polynomial `poly`.
Parameters
----------
t : ndarray
Times at which to evaluate the waveform.
poly : 1-D array-like or instance of numpy.poly1d
The desired frequency expressed as a polynomial. If `poly` is
a list or ndarray of length n, then the elements of `poly` are
the coefficients of the polynomial, and the instantaneous
frequency is
``f(t) = poly[0]*t**(n-1) + poly[1]*t**(n-2) + ... + poly[n-1]``
If `poly` is an instance of numpy.poly1d, then the
instantaneous frequency is
``f(t) = poly(t)``
phi : float, optional
Phase offset, in degrees, Default: 0.
Returns
-------
sweep_poly : ndarray
A numpy array containing the signal evaluated at `t` with the
requested time-varying frequency. More precisely, the function
returns ``cos(phase + (pi/180)*phi)``, where `phase` is the integral
(from 0 to t) of ``2 * pi * f(t)``; ``f(t)`` is defined above.
See Also
--------
chirp
Notes
-----
.. versionadded:: 0.8.0
If `poly` is a list or ndarray of length `n`, then the elements of
`poly` are the coefficients of the polynomial, and the instantaneous
frequency is:
``f(t) = poly[0]*t**(n-1) + poly[1]*t**(n-2) + ... + poly[n-1]``
If `poly` is an instance of `numpy.poly1d`, then the instantaneous
frequency is:
``f(t) = poly(t)``
Finally, the output `s` is:
``cos(phase + (pi/180)*phi)``
where `phase` is the integral from 0 to `t` of ``2 * pi * f(t)``,
``f(t)`` as defined above.
"""
# 'phase' is computed in _sweep_poly_phase, to make testing easier.
phase = _sweep_poly_phase(t, poly)
# Convert to radians.
phi *= pi / 180
return cos(phase + phi)
def _sweep_poly_phase(t, poly):
"""
Calculate the phase used by sweep_poly to generate its output.
See `sweep_poly` for a description of the arguments.
"""
# polyint handles lists, ndarrays and instances of poly1d automatically.
intpoly = polyint(poly)
phase = 2 * pi * polyval(intpoly, t)
return phase
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