How to calculate Σ p(x) dx?

Σp(x)dx

[James Tursa]

Looks like you are asking how to integrate a function. Can you show us the function you are working with and the range over which you want to integrate?

[Walter Roberson]

Σ is for summation, but dx represents infinitesimal, so you would get zero as the result unless it was the infinite summation.

If you were talking about using a summation to approximate an integral in the limiting case, then the notation that would be used for that would be

[James Tursa]

@Walter: I think you meant just

[meenu v]

i want to calculate S= 4* √ Σ psd(f) df

[Walter Roberson]

d notation is used for infinitesimals, which have to be integrated rather than summed. For finite quantities delta notation is used and indication of the summation limits would be given.

Anyhow see

https://www.mathworks.com/help/signal/ref/dspdata.psd.html

https://www.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html