Pwelch only returns a single value?

1 次查看（过去 30 天）
Shayma Al Ali
Shayma Al Ali 2022-2-25
回答： Shushant 2023-9-25
I am trying to use the pwelch method in order to calculate the coherence magnitude squared between two signals with confidence intervals. However, the pwelch function only returns a single value. What am I doing wrong?
I also attached the variables I use in my code.
My code:
%calculate pwelch
fs=1/i_ph1.spacing_l;
[pwelch_1,f1,pxx1]=pwelch(i_ph1.l,hanning(length(i_ph1.l)),(length(i_ph1.l))/2,fs,'ConfidenceLevel',0.95);
[pwelch_2,f2,pxx2]=pwelch(i_ph2.l,hanning(length(i_ph2.l)),(length(i_ph2.l))/2,fs,'ConfidenceLevel',0.95);
[pwelch_3,f3,pxx3]=pwelch(i_ph3.l,hanning(length(i_ph3.l)),(length(i_ph3.l))/2,fs,'ConfidenceLevel',0.95);
[pwelch_12,f12,pxx12]=pwelch(xcorr(i_ph1.l,i_ph2.l),hanning(length(i_ph1.l)),(length(i_ph1.l))/2,fs,'ConfidenceLevel',0.95);
[pwelch_23,f23,pxx23]=pwelch(xcorr(i_ph2.l,i_ph3.l),hanning(length(i_ph2.l)),(length(i_ph2.l))/2,fs,'ConfidenceLevel',0.95);
[pwelch_31,f13,pxx13]=pwelch(xcorr(i_ph3.l,i_ph1.l),hanning(length(i_ph3.l)),(length(i_ph3.l))/2,fs,'ConfidenceLevel',0.95);
%calculate CMS
%Pxy^2/Pxx*Pyy
CMS12=(pwelch_12).^2./(pwelch_1.*pwelch_2);
CMS23=(pwelch_23).^2./(pwelch_2.*pwelch_3);
CMS13=(pwelch_31).^2./(pwelch_3.*pwelch_1);
%calculate CMS of conf intervals
CMS_c13=(pxx12).^2./(pxx1.*pxx2);
CMS_c23=(pxx23).^2./(pxx2.*pxx3);
CMS_c13=(pxx13).^2./(pxx1.*pxx3);
  1 个评论
Mathieu NOE
Mathieu NOE 2022-3-8
hello
have you tried mscohere ?
help mscohere
mscohere Magnitude Squared Coherence Estimate.
Cxy = mscohere(X,Y) estimates the magnitude squared coherence estimate
of the system with input X and output Y using Welch's averaged,
modified periodogram method. Coherence is a function of frequency with
values between 0 and 1 that indicate how well the input X corresponds
to the output Y at each frequency. The magnitude squared coherence,
Cxy, is given by Cxy = (abs(Pxy).^2)./(Pxx.*Pyy) where Pxx and Pyy are
the power spectral density (PSD) estimate of X and Y, respectively; and
Pxy is the Cross-PSD (CPSD) estimate of X and Y. See "help pwelch" and
"help cpsd" for complete details.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Shushant
Shushant 2023-9-25
Hi Shayma Al Ali,
I understand that you are using the "pwelch" function to calculate the coherence magnitude squared between two signals with confidence intervals. But the function is only returning a single value. This is because the "pwelch" function is expecting "fs" to be the fifth argument.
To solve this issue, specify the fourth argument as empty "[]". Refer to the following code snippet for the modified function call:
[pwelch_1,f1,pxx1]=pwelch(i_ph1.l,hanning(length(i_ph1.l)),(length(i_ph1.l))/2,[],fs,'ConfidenceLevel',0.95);
Refer to the following documentation for information on why the fourth argument should be empty-
https://in.mathworks.com/help/signal/ref/pwelch.html
I hope this helped in solving the issue you were facing.
Thank you,
Shushant

类别

在 Help Center 和 File Exchange 中查找有关 Spectral Estimation 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by