Network functions.vi

[celynn]

Hi, Any idea how can i use the Network function.vi to calculate the coherence between n number of  time-signals?

[ChrisJ]

Hi Celynn,

Can you give us a little more information on what you are trying to do?

Thanks!

Chris J

[celynn]

say i got 4 signals, w x y z . i want to calculate the coherence between the four signals.

ie coherence with wx wy wz etc.

[ChrisJ]

Celynn,

You will need to use a separate instance of the function for every set of values that you want to check the coherence between. You will need to pass in a 2D array for both the Stimulus Signal and Response signal for the function to work properly. In the Stimulus input each row will correspond to a frame of the network stimulus. In the Response input each row will correspond to a frame of the network response. You can find more information on this function by right clicking on the VI and selecting 'Help'.

Regards,

Chris J

[celynn]

Hi, please advise me why the coherence values are all 1?i am not expecting this result as both the signals are not the same

and how do i plot my cross power spectrum(avg) in dB?

[ChrisJ]

Hi Celynn,

Well it is difficult to tell from the picture, but it looks like you are just passing two data sets into the network functions VI. To use this function you must have multiple samples of both the stimuli and the response. If you only pass one sample of each it will return a very high (~1) coherence. The reason is that is has no way to tell if the response is correct or not. If your stimulus is a sine wave and your response is a square wave, there is no way for the function to know if that is the expected outcome or not. Perhaps your system always returns a square wave in response to a sine wave stimulus. The only way to tell is to get multiple samples of data. If the stimuli is always the same and the response is random then the coherence will go down. However, if the stimuli is always the same and the response is always the same then the coherence will be 1. If you only have one sample of each then the coherence is by default 1.

Regards,
Chris J