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Member of the spectral analysis class.

Syntax

cohere(x, y)

cohere(x, y, nfft, fs, window)

cohere(x, y, nfft, fs, window, noverlap)

cohere(x, y, nfft, fs, window, noverlap, flag)

Rxy = cohere(x, y)

Rxy = cohere(x, y, nfft, fs, window)

Rxy = cohere(x, y, nfft, fs, window, noverlap)

Rxy = cohere(x, y, nfft, fs, window, noverlap, flag)

[Rxy, f] = cohere(x, y)

[Rxy, f] = cohere(x, y, nfft, fs, window)

[Rxy, f] = cohere(x, y, nfft, fs, window, noverlap)

[Rxy, f] = cohere(x, y, nfft, fs, window, noverlap, flag)

Description

Uses the Welch method to estimate the coherence of two signals. If you do not specify an output, this function plots the coherence in the current plot window.

Details

Examples

Inputs

Name	Description
x	Specifies the first input sequence.
y	Specifies the second input sequence. length(y) must equal length(x).
nfft	Specifies the length of the FFT to perform on each segment of data. The default is the minimum of 256 and the length of x.
fs	Specifies the sampling frequency. The default is 2.
window	Specifies the window to apply to x and y. The length of the window must be less than or equal to nfft. The default is a Hanning window with a length of nfft.
noverlap	Specifies the number of overlapping data elements between adjacent segments of data. noverlap must be less than the length of window. The default is 0.
flag	Specifies the method to use to preprocess x and y before applying the window. flag is a string that accepts the following values. 'linear' LabVIEW removes the best linear fit of each segment of data. 'mean' LabVIEW removes the mean of each segment of data. 'none' (default) LabVIEW does not preprocess x and y.

Outputs

Name	Description
Rxy	Returns the coherence of the input signals x and y. If x and y are real, the length of Rxy is nfft/2 + 1 for an even nfft and (nfft + 1) / 2 for an odd nfft. If x and y are complex, the length of Rxy is nfft.
f	Returns the frequencies that correspond to Rxy.

Details

This function uses the Welch method to compute the power spectrum of x, the power spectrum of y, and the cross power spectrum of x and y. LabVIEW uses the following equation to compute the coherence of x and y: R_xy(f) = |P_xy(f)|^2/(P_xx(f)*P_yy(f))

This function is supported in the LabVIEW Run-Time Engine only if you request an output from the function. This function can remain in your scripts when you build a stand-alone application or shared library, but if you do not request an output, the LabVIEW Run-Time Engine does not execute this function. If you request an output, the LabVIEW Run-Time Engine executes this function as normal.

Examples

fs = 1000;
T = 2;
t = 0:1 / fs:T - 1 / fs;
nfft = 256;
noverlap = nfft / 2;
window = hanning(nfft);
dflag = 'none';
xn = sin(2*pi*100*t) + randn(1, length(t));
h = fir1(5, 0.2, 'low', hanning(6));
yn = filter(h, 1, xn);
[Rxy, f] = cohere(xn, yn, nfft, fs, window, noverlap, dflag);

Related Topics

csd
filter
fir1
hanning
randn
sin
tfe