Import pywt first
>>> import pywt
>>> def format_array(a):
... """Consistent array representation across different systems"""
... import numpy
... a = numpy.where(numpy.abs(a) < 1e-5, 0, a)
... return numpy.array2string(a, precision=5, separator=' ', suppress_small=True)
List of availble signal extension modes:
>>> print pywt.MODES.modes
['zpd', 'cpd', 'sym', 'ppd', 'sp1', 'per']
Test that dwt() and idwt() can be performed using every mode:
>>> x = [1,2,1,5,-1,8,4,6]
>>> for mode in pywt.MODES.modes:
... cA, cD = pywt.dwt(x, 'db2', mode)
... print "Mode:", mode
... print "cA:", format_array(cA)
... print "cD:", format_array(cD)
... print "Reconstruction:", pywt.idwt(cA, cD, 'db2', mode)
Mode: zpd
cA: [-0.03468 1.73309 3.40612 6.32929 6.95095]
cD: [-0.12941 -2.156 -5.95035 -1.21545 -1.8625 ]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: cpd
cA: [ 1.2848 1.73309 3.40612 6.32929 7.51936]
cD: [-0.48296 -2.156 -5.95035 -1.21545 0.25882]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: sym
cA: [ 1.76777 1.73309 3.40612 6.32929 7.77817]
cD: [-0.61237 -2.156 -5.95035 -1.21545 1.22474]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: ppd
cA: [ 6.91627 1.73309 3.40612 6.32929 6.91627]
cD: [-1.99191 -2.156 -5.95035 -1.21545 -1.99191]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: sp1
cA: [-0.51764 1.73309 3.40612 6.32929 7.45001]
cD: [ 0. -2.156 -5.95035 -1.21545 0. ]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: per
cA: [ 4.05317 3.05257 2.85381 8.42522]
cD: [ 0.18947 4.18258 4.33738 2.60428]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Invalid mode name should rise a ValueError:
>>> pywt.dwt([1,2,3,4], 'db2', 'invalid')
Traceback (most recent call last):
...
ValueError: Unknown mode name 'invalid'.
You can also refer to modes via MODES class attributes:
>>> for mode_name in ['zpd', 'cpd', 'sym', 'ppd', 'sp1', 'per']:
... mode = getattr(pywt.MODES, mode_name)
... cA, cD = pywt.dwt([1,2,1,5,-1,8,4,6], 'db2', mode)
... print "Mode:", mode, "(%s)" % mode_name
... print "cA:", format_array(cA)
... print "cD:", format_array(cD)
... print "Reconstruction:", pywt.idwt(cA, cD, 'db2', mode)
Mode: 0 (zpd)
cA: [-0.03468 1.73309 3.40612 6.32929 6.95095]
cD: [-0.12941 -2.156 -5.95035 -1.21545 -1.8625 ]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: 2 (cpd)
cA: [ 1.2848 1.73309 3.40612 6.32929 7.51936]
cD: [-0.48296 -2.156 -5.95035 -1.21545 0.25882]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: 1 (sym)
cA: [ 1.76777 1.73309 3.40612 6.32929 7.77817]
cD: [-0.61237 -2.156 -5.95035 -1.21545 1.22474]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: 4 (ppd)
cA: [ 6.91627 1.73309 3.40612 6.32929 6.91627]
cD: [-1.99191 -2.156 -5.95035 -1.21545 -1.99191]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: 3 (sp1)
cA: [-0.51764 1.73309 3.40612 6.32929 7.45001]
cD: [ 0. -2.156 -5.95035 -1.21545 0. ]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Mode: 5 (per)
cA: [ 4.05317 3.05257 2.85381 8.42522]
cD: [ 0.18947 4.18258 4.33738 2.60428]
Reconstruction: [ 1. 2. 1. 5. -1. 8. 4. 6.]
Some invalid mode values:
>>> pywt.dwt(x, 'db2', -1)
Traceback (most recent call last):
...
ValueError: Invalid mode.
>>> pywt.dwt(x, 'db2', 7)
Traceback (most recent call last):
...
ValueError: Invalid mode.
>>> pywt.dwt(x, 'db2', None)
Traceback (most recent call last):
...
TypeError: expected string or Unicode object, NoneType found
The default mode is sym:
>>> cA, cD = pywt.dwt(x, 'db2')
>>> print cA
[ 1.76776695 1.73309178 3.40612438 6.32928585 7.77817459]
>>> print cD
[-0.61237244 -2.15599552 -5.95034847 -1.21545369 1.22474487]
>>> print pywt.idwt(cA, cD, 'db2')
[ 1. 2. 1. 5. -1. 8. 4. 6.]
And using a keyword argument:
>>> cA, cD = pywt.dwt(x, 'db2', mode='sym')
>>> print cA
[ 1.76776695 1.73309178 3.40612438 6.32928585 7.77817459]
>>> print cD
[-0.61237244 -2.15599552 -5.95034847 -1.21545369 1.22474487]
>>> print pywt.idwt(cA, cD, 'db2')
[ 1. 2. 1. 5. -1. 8. 4. 6.]