- #1
jpreed
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I have been reading papers for my research and I came across this equation twice:
[tex]\lim_{\eta\to 0+}\frac{1}{x+i \eta} = P\left(\frac{1}{x}\right) - i \pi \delta(x)[/tex]
Where P is the pricipal part.
It has been quite a while since I have had complex variables, but might it come from the residue theorem? If anyone knows the origin of this identity and how it is derived, I would love to see it.
Thanks!
Edit: added images
Here are clips from the two papers below. In the second clip, the sum over eta is implied.
[tex]\lim_{\eta\to 0+}\frac{1}{x+i \eta} = P\left(\frac{1}{x}\right) - i \pi \delta(x)[/tex]
Where P is the pricipal part.
It has been quite a while since I have had complex variables, but might it come from the residue theorem? If anyone knows the origin of this identity and how it is derived, I would love to see it.
Thanks!
Edit: added images
Here are clips from the two papers below. In the second clip, the sum over eta is implied.
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