matplotlib.axes.Axes.csd¶

Axes.
csd
(self, x, y, NFFT=None, Fs=None, Fc=None, detrend=None, window=None, noverlap=None, pad_to=None, sides=None, scale_by_freq=None, return_line=None, \*, data=None, \*\*kwargs)[source]¶ Plot the crossspectral density.
The cross spectral density \(P_{xy}\) by Welch's average periodogram method. The vectors x and y are divided into NFFT length segments. Each segment is detrended by function detrend and windowed by function window. noverlap gives the length of the overlap between segments. The product of the direct FFTs of x and y are averaged over each segment to compute \(P_{xy}\), with a scaling to correct for power loss due to windowing.
If len(x) < NFFT or len(y) < NFFT, they will be zero padded to NFFT.
Parameters:  x, y1D arrays or sequences
Arrays or sequences containing the data.
 Fsscalar
The sampling frequency (samples per time unit). It is used to calculate the Fourier frequencies, freqs, in cycles per time unit. The default value is 2.
 windowcallable or ndarray
A function or a vector of length NFFT. To create window vectors see
window_hanning
,window_none
,numpy.blackman
,numpy.hamming
,numpy.bartlett
,scipy.signal
,scipy.signal.get_window
, etc. The default iswindow_hanning
. If a function is passed as the argument, it must take a data segment as an argument and return the windowed version of the segment. sides{'default', 'onesided', 'twosided'}
Specifies which sides of the spectrum to return. Default gives the default behavior, which returns onesided for real data and both for complex data. 'onesided' forces the return of a onesided spectrum, while 'twosided' forces twosided.
 pad_toint
The number of points to which the data segment is padded when performing the FFT. This can be different from NFFT, which specifies the number of data points used. While not increasing the actual resolution of the spectrum (the minimum distance between resolvable peaks), this can give more points in the plot, allowing for more detail. This corresponds to the n parameter in the call to fft(). The default is None, which sets pad_to equal to NFFT
 NFFTint
The number of data points used in each block for the FFT. A power 2 is most efficient. The default value is 256. This should NOT be used to get zero padding, or the scaling of the result will be incorrect. Use pad_to for this instead.
 detrend{'none', 'mean', 'linear'} or callable, default 'none'
The function applied to each segment before ffting, designed to remove the mean or linear trend. Unlike in MATLAB, where the detrend parameter is a vector, in Matplotlib is it a function. The
mlab
module definesdetrend_none
,detrend_mean
, anddetrend_linear
, but you can use a custom function as well. You can also use a string to choose one of the functions: 'none' callsdetrend_none
. 'mean' callsdetrend_mean
. 'linear' callsdetrend_linear
. scale_by_freqbool, optional
Specifies whether the resulting density values should be scaled by the scaling frequency, which gives density in units of Hz^1. This allows for integration over the returned frequency values. The default is True for MATLAB compatibility.
 noverlapint
The number of points of overlap between segments. The default value is 0 (no overlap).
 Fcint
The center frequency of x (defaults to 0), which offsets the x extents of the plot to reflect the frequency range used when a signal is acquired and then filtered and downsampled to baseband.
 return_linebool
Whether to include the line object plotted in the returned values. Default is False.
Returns:  Pxy1D array
The values for the cross spectrum
P_{xy}
before scaling (complex valued). freqs1D array
The frequencies corresponding to the elements in Pxy.
 line
Line2D
The line created by this function. Only returned if return_line is True.
Other Parameters:  **kwargs
Keyword arguments control the
Line2D
properties:Property Description agg_filter
a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array alpha
float or None animated
bool antialiased
or aabool clip_box
Bbox
clip_on
bool clip_path
Patch or (Path, Transform) or None color
or ccolor contains
callable dash_capstyle
{'butt', 'round', 'projecting'} dash_joinstyle
{'miter', 'round', 'bevel'} dashes
sequence of floats (on/off ink in points) or (None, None) data
(2, N) array or two 1D arrays drawstyle
or ds{'default', 'steps', 'stepspre', 'stepsmid', 'stepspost'}, default: 'default' figure
Figure
fillstyle
{'full', 'left', 'right', 'bottom', 'top', 'none'} gid
str in_layout
bool label
object linestyle
or ls{'', '', '.', ':', '', (offset, onoffseq), ...} linewidth
or lwfloat marker
marker style markeredgecolor
or meccolor markeredgewidth
or mewfloat markerfacecolor
or mfccolor markerfacecoloralt
or mfcaltcolor markersize
or msfloat markevery
None or int or (int, int) or slice or List[int] or float or (float, float) path_effects
AbstractPathEffect
picker
float or callable[[Artist, Event], Tuple[bool, dict]] pickradius
float rasterized
bool or None sketch_params
(scale: float, length: float, randomness: float) snap
bool or None solid_capstyle
{'butt', 'round', 'projecting'} solid_joinstyle
{'miter', 'round', 'bevel'} transform
matplotlib.transforms.Transform
url
str visible
bool xdata
1D array ydata
1D array zorder
float
Notes
For plotting, the power is plotted as \(10 \log_{10}(P_{xy})\) for decibels, though
P_{xy}
itself is returned.References
Bendat & Piersol  Random Data: Analysis and Measurement Procedures, John Wiley & Sons (1986)
Note
In addition to the above described arguments, this function can take a data keyword argument. If such a data argument is given, the following arguments are replaced by data[<arg>]:
 All arguments with the following names: 'x', 'y'.
Objects passed as data must support item access (
data[<arg>]
) and membership test (<arg> in data
).