[Scipysvn] r6975  in trunk/scipy/signal: . tests
scipysvn@scip...
scipysvn@scip...
Sun Nov 28 18:40:49 CST 2010
Author: warren.weckesser
Date: 20101128 18:40:49 0600 (Sun, 28 Nov 2010)
New Revision: 6975
Modified:
trunk/scipy/signal/fir_filter_design.py
trunk/scipy/signal/tests/test_fir_filter_design.py
Log:
ENH: signal: add the 'nyq' keyword argument to firwin(), to be consistent with the API of firwin2().
Modified: trunk/scipy/signal/fir_filter_design.py
===================================================================
 trunk/scipy/signal/fir_filter_design.py 20101128 23:43:20 UTC (rev 6974)
+++ trunk/scipy/signal/fir_filter_design.py 20101129 00:40:49 UTC (rev 6975)
@@ 129,7 +129,8 @@
return int(ceil(numtaps)), beta
def firwin(numtaps, cutoff, width=None, window='hamming', pass_zero=True, scale=True):
+def firwin(numtaps, cutoff, width=None, window='hamming', pass_zero=True,
+ scale=True, nyq=1.0):
"""
FIR filter design using the window method.
@@ 145,25 +146,25 @@

numtaps : int
Length of the filter (number of coefficients, i.e. the filter
 order + 1). `numtaps` must be even if a passband includes the Nyquist
 frequency.
+ order + 1). `numtaps` must be even if a passband includes the
+ Nyquist frequency.
cutoff : float or 1D array_like
 Cutoff frequency of filter (normalized so that 1 corresponds to
 Nyquist or pi radians / sample) OR an array of cutoff frequencies
 (that is, band edges). In the latter case, the frequencies in
 `cutoff` should be positive and monotonically increasing between
 0 and 1. The values 0 and 1 must not be included in `cutoff`.
+ Cutoff frequency of filter (expressed in the same units as `nyq`)
+ OR an array of cutoff frequencies (that is, band edges). In the
+ latter case, the frequencies in `cutoff` should be positive and
+ monotonically increasing between 0 and `nyq`. The values 0 and
+ `nyq` must not be included in `cutoff`.
width : float or None
 If `width` is not None, then assume it is the approximate width of
 the transition region (normalized so that 1 corresponds to pi)
+ If `width` is not None, then assume it is the approximate width
+ of the transition region (expressed in the same units as `nyq`)
for use in Kaiser FIR filter design. In this case, the `window`
argument is ignored.
window : string or tuple of string and parameter values
 Desired window to use. See `scipy.signal.get_window` for a list of
 windows and required parameters.
+ Desired window to use. See `scipy.signal.get_window` for a list
+ of windows and required parameters.
pass_zero : bool
If True, the gain at the frequency 0 (i.e. the "DC gain") is 1.
@@ 175,10 +176,14 @@
That frequency is either:
0 (DC) if the first passband starts at 0 (i.e. pass_zero
is True);
 1 (Nyquist) if the first passband ends at 1 (i.e the
 filter is a single band highpass filter);
+ `nyq` (the Nyquist rate) if the first passband ends at
+ `nyq` (i.e the filter is a single band highpass filter);
center of first passband otherwise.
+ nyq : float
+ Nyquist frequency. Each frequency in `cutoff` must be between 0
+ and `nyq`.
+
Returns

h : 1D ndarray
@@ 187,8 +192,8 @@
Raises

ValueError
 If any value in cutoff is less than or equal to 0 or greater
 than or equal to 1, if the values in cutoff are not strictly
+ If any value in `cutoff` is less than or equal to 0 or greater
+ than or equal to `nyq`, if the values in `cutoff` are not strictly
monotonically increasing, or if `numtaps` is even but a passband
includes the Nyquist frequency.
@@ 232,28 +237,24 @@
# The major enhancements to this function added in November 2010 were
# developed by Tom Krauss (see ticket #902).
 cutoff = np.atleast_1d(cutoff)

+ cutoff = np.atleast_1d(cutoff) / float(nyq)
+
# Check for invalid input.
if cutoff.ndim > 1:
raise ValueError("The cutoff argument must be at most onedimensional.")
if cutoff.size == 0:
raise ValueError("At least one cutoff frequency must be given.")
if cutoff.min() <= 0 or cutoff.max() >= 1:
 raise ValueError("Invalid cutoff frequency: frequencies must be greater than 0 and less than 1.")
+ raise ValueError("Invalid cutoff frequency: frequencies must be greater than 0 and less than nyq.")
if np.any(np.diff(cutoff) <= 0):
raise ValueError("Invalid cutoff frequencies: the frequencies must be strictly increasing.")
if width is not None:
 # A width was given. Verify that it is a float, find the beta parameter
 # of the Kaiser window, and set `window`. This overrides the value of
 # `window` passed in.
 if isinstance(width, float):
 atten = kaiser_atten(numtaps, width)
 beta = kaiser_beta(atten)
 window = ('kaiser', beta)
 else:
 raise ValueError("Invalid value for width: %s", width)
+ # A width was given. Find the beta parameter of the Kaiser window
+ # and set `window`. This overrides the value of `window` passed in.
+ atten = kaiser_atten(numtaps, float(width)/nyq)
+ beta = kaiser_beta(atten)
+ window = ('kaiser', beta)
pass_nyquist = bool(cutoff.size & 1) ^ pass_zero
if pass_nyquist and numtaps % 2 == 0:
Modified: trunk/scipy/signal/tests/test_fir_filter_design.py
===================================================================
 trunk/scipy/signal/tests/test_fir_filter_design.py 20101128 23:43:20 UTC (rev 6974)
+++ trunk/scipy/signal/tests/test_fir_filter_design.py 20101129 00:40:49 UTC (rev 6975)
@@ 165,6 +165,25 @@
[1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0],
decimal=5)
+ def test_nyq(self):
+ """Test the nyq keyword."""
+ nyquist = 1000
+ width = 40.0
+ relative_width = width/nyquist
+ ntaps, beta = kaiserord(120, relative_width)
+ taps = firwin(ntaps, cutoff=[300, 700], window=('kaiser', beta),
+ pass_zero=False, scale=False, nyq=nyquist)
+
+ # Check the symmetry of taps.
+ assert_array_almost_equal(taps[:ntaps/2], taps[ntaps:ntapsntaps/21:1])
+
+ # Check the gain at a few samples where we know it should be approximately 0 or 1.
+ freq_samples = np.array([0.0, 200, 300width/2, 300+width/2, 500,
+ 700width/2, 700+width/2, 800, 1000])
+ freqs, response = freqz(taps, worN=np.pi*freq_samples/nyquist)
+ assert_array_almost_equal(np.abs(response),
+ [0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0], decimal=5)
+
def test_bad_cutoff(self):
"""Test that invalid cutoff argument raises ValueError."""
# cutoff values must be greater than 0 and less than 1.
@@ 180,8 +199,10 @@
assert_raises(ValueError, firwin, 99, [])
# 2D array not allowed.
assert_raises(ValueError, firwin, 99, [[0.1, 0.2],[0.3, 0.4]])
+ # cutoff values must be less than nyq.
+ assert_raises(ValueError, firwin, 99, 50.0, nyq=40)
+ assert_raises(ValueError, firwin, 99, [10, 20, 30], nyq=25)

def test_even_highpass_raises_value_error(self):
"""Test that attempt to create a highpass filter with an even number
of taps raises a ValueError exception."""
@@ 190,6 +211,7 @@
+
class TestFirwin2(TestCase):
def test_invalid_args(self):
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