# mne.time_frequency.CrossSpectralDensity¶

class mne.time_frequency.CrossSpectralDensity(data, ch_names, frequencies, n_fft, tmin=None, tmax=None, projs=None)[source]

Cross-spectral density.

Given a list of time series, the CSD matrix denotes for each pair of time series, the cross-spectral density. This matrix is symmetric and internally stored as a vector.

This object can store multiple CSD matrices: one for each frequency. Use .get_data(freq) to obtain an CSD matrix as an ndarray.

Parameters
datandarray, shape ((n_channels**2 + n_channels) / 2, n_frequencies)

For each frequency, the cross-spectral density matrix in vector format.

ch_names

List of string names for each channel.

frequencies

Frequency or frequencies for which the CSD matrix was calculated. When averaging across frequencies (see the CrossSpectralDensity.mean() function), this will be a list of lists that contains for each frequency bin, the frequencies that were averaged. Frequencies should always be sorted.

n_fftint

The number of FFT points or samples that have been used in the computation of this CSD.

tmin

Start of the time window for which CSD was calculated in seconds. Can be None (the default) to indicate no timing information is available.

tmax

End of the time window for which CSD was calculated in seconds. Can be None (the default) to indicate no timing information is available.

projs

List of projectors to apply to timeseries data when using this CSD object to compute a DICS beamformer. Defaults to None, which means no projectors will be applied.

Attributes
n_channels

Number of time series defined in this CSD object.

Methods

 __getitem__(self, sel) Subselect frequencies. __hash__(self, /) Return hash(self). __len__(self) Return number of frequencies. copy(self) Return copy of the CrossSpectralDensity object. get_data(self[, frequency, index]) Get the CSD matrix for a given frequency as NumPy array. mean(self[, fmin, fmax]) Calculate the mean CSD in the given frequency range(s). pick_frequency(self[, freq, index]) Get a CrossSpectralDensity object with only the given frequency. plot(self[, info, mode, colorbar, cmap, …]) Plot CSD matrices. save(self, fname) Save the CSD to an HDF5 file. sum(self[, fmin, fmax]) Calculate the sum CSD in the given frequency range(s).
__getitem__(self, sel)[source]

Subselect frequencies.

Parameters
selndarray

Array of frequency indices to subselect.

Returns
csdinstance of CrossSpectralDensity

A new CSD instance with the subset of frequencies.

__hash__(self, /)

Return hash(self).

__len__(self)[source]

Return number of frequencies.

Returns
n_freqsint

The number of frequencies.

copy(self)[source]

Return copy of the CrossSpectralDensity object.

get_data(self, frequency=None, index=None)[source]

Get the CSD matrix for a given frequency as NumPy array.

If there is only one matrix defined in the CSD object, calling this method without any parameters will return it. If multiple matrices are defined, use either the frequency or index parameter to select one.

Parameters
frequency

Return the CSD matrix for a specific frequency. Only available when no averaging across frequencies has been done.

index

Return the CSD matrix for the frequency or frequency-bin with the given index.

Returns
csdndarray, shape (n_channels, n_channels)

The CSD matrix corresponding to the requested frequency.

mean(self, fmin=None, fmax=None)[source]

Calculate the mean CSD in the given frequency range(s).

Parameters
fmin

Lower bound of the frequency range in Hertz. Defaults to the lowest frequency available. When a list of frequencies is given, these are used as the lower bounds (inclusive) of frequency bins and the mean is taken for each bin.

fmax

Upper bound of the frequency range in Hertz. Defaults to the highest frequency available. When a list of frequencies is given, these are used as the upper bounds (inclusive) of frequency bins and the mean is taken for each bin.

Returns
csdinstance of CrossSpectralDensity

The CSD matrix, averaged across the given frequency range(s).

Examples using mean:

property n_channels

Number of time series defined in this CSD object.

pick_frequency(self, freq=None, index=None)[source]

Get a CrossSpectralDensity object with only the given frequency.

Parameters
freq

Return the CSD matrix for a specific frequency. Only available when no averaging across frequencies has been done.

index

Return the CSD matrix for the frequency or frequency-bin with the given index.

Returns
csdinstance of CrossSpectralDensity

A CSD object containing a single CSD matrix that corresponds to the requested frequency or frequency-bin.

plot(self, info=None, mode='csd', colorbar=True, cmap='viridis', n_cols=None, show=True)[source]

Plot CSD matrices.

A sub-plot is created for each frequency. If an info object is passed to the function, different channel types are plotted in different figures.

Parameters
info: instance of Info | None

To split the figure by channel-type, provide the measurement info. By default, the CSD matrix is plotted as a whole.

mode‘csd’ | ‘coh’

Whether to plot the cross-spectral density (‘csd’, the default), or the coherence (‘coh’) between the channels.

colorbarbool

Whether to show a colorbar. Defaults to True.

cmap

The matplotlib colormap to use. Defaults to None, which means the colormap will default to matplotlib’s default.

n_cols

CSD matrices are plotted in a grid. This parameter controls how many matrix to plot side by side before starting a new row. By default, a number will be chosen to make the grid as square as possible.

showbool

Whether to show the figure. Defaults to True.

Returns
fig

The figures created by this function.

save(self, fname)[source]

Save the CSD to an HDF5 file.

Parameters
fnamestr

The name of the file to save the CSD to. The extension ‘.h5’ will be appended if the given filename doesn’t have it already.

read_csd

For reading CSD objects from a file.

sum(self, fmin=None, fmax=None)[source]

Calculate the sum CSD in the given frequency range(s).

If the exact given frequencies are not available, the nearest frequencies will be chosen.

Parameters
fmin

Lower bound of the frequency range in Hertz. Defaults to the lowest frequency available. When a list of frequencies is given, these are used as the lower bounds (inclusive) of frequency bins and the sum is taken for each bin.

fmax

Upper bound of the frequency range in Hertz. Defaults to the highest frequency available. When a list of frequencies is given, these are used as the upper bounds (inclusive) of frequency bins and the sum is taken for each bin.

Returns
csdinstance of CrossSpectralDensity

The CSD matrix, summed across the given frequency range(s).

Examples using sum: