Thursday, July 30, 2015

Pole Dancing

From the previous post "Clock Face And Life, Two Pies And Habits" dated 30 Jul 2015,

\(\int ^{\infty}_{-\infty}{ f(z)d(e^{- i\theta  }) }=-\int^{\infty}_{-\infty}{it.g(\omega t)e^{-i\omega t}}d\,\omega=-it.G(t)\)

if instead,

\(\int ^{\infty}_{-\infty}{ f(z)d(e^{- i\theta  }) }=-\int^{\infty}_{-\infty}{i\omega.g(\omega t)e^{-i\omega t}}d\,t=-i\omega.G(\omega)\)

which is exactly Fourier.  However,

since,  \(\theta=\omega t\),   \(\omega=2\pi.\cfrac{1}{T}\)

\(t=\cfrac{T}{2\pi}\theta\)

and

\(\int ^{\infty}_{-\infty}{ f(z)d(e^{- i\theta  }) }=-i\cfrac{T}{2\pi}\theta.G(\cfrac{T}{2\pi}\theta)\)

If I go fishing,

\(\int ^{\infty}_{-\infty}{\cfrac{h(z)}{(z-z_o)}d(e^{ -i\theta  }+z_o) }=-i\cfrac{T}{2\pi}\theta.G(\cfrac{T}{2\pi}\theta)\) --- (*)

where \(f(z)=\cfrac{h(z)}{(z-z_o)}\), \(z_o\) a complex constant.

from the post "What Holomorphic?" dated 30 Jul 2015.  When we consider \(-\infty\)  to  \(\infty\) as the biggest close loop possible.  From Cauchy's integral formula,

\(h(z_o)=\cfrac{1}{2\pi i}\oint_c{\cfrac{h(z)}{(z-z_o)}}dz\)

Unfortunately on the complex plane, \(z_o\) cannot just disappear; is (*) still valid?  If so,

\(\oint_c{\cfrac{h(z)}{(z-z_o)}}dz=\int ^{\infty}_{-\infty}{\cfrac{h(z)}{(z-z_o)}d(e^{ -i\theta  }+z_o) }\)

\(2\pi ih(z_o)=i\cfrac{T}{2\pi}\theta_{z_o}. g\left(\cfrac{T }{2\pi}\theta_{z_o} \right)\)

\(h(z_o)=\cfrac{T}{(2\pi)^2}\theta_{z_o}. g\left(\cfrac{T }{2\pi}\theta_{z_o} \right)\)

where \(z_o=R_{\theta_{zo}}e^{i\theta_{zo}}\)

\(h(z_o)\) depends on \(\theta_{z_o}\) only.  Which is very odd, I loop around a pole with \(e^{-i\theta}\) but it does not matter how long my reach is.

This must be wrong.  Previously, the dependence on \(R_\theta\) disappeared because I am always on a unit circle.  If we change \(e^{-i\theta}\to R_{zo}e^{-i\theta}\) such that we loop around \(z_o\),

\(\int ^{\infty}_{-\infty}{\cfrac{h(z)}{(z-z_o)}d(R_{zo}e^{- i\theta  }) }=R_{zo}.i\cfrac{T}{2\pi}\theta. g\left(\cfrac{T }{2\pi}\theta \right)\)

then,

\(h(z_o)=R_{zo}.\cfrac{T}{(2\pi)^2}\theta_{z_o}. g\left(\cfrac{T }{2\pi}\theta_{z_o} \right)\)

provided \(z_o\) is the only pole within the circle \(R_{zo}e^{-i\theta}\).  Still,

\(\oint_c{\cfrac{h(z)}{(z-z_o)}}dz\ne \int ^{\infty}_{-\infty}{\cfrac{h(z)}{(z-z_o)}d(R_{zo}e^{- i\theta  }) }\)

And this is all wrong.  Unless \(\oint_c{...}dz\) allows us to go around in circle specifically.

\(\oint_c{\cfrac{h(z)}{(z-z_o)}}dz=\oint_{cR}{\cfrac{h(z)}{(z-z_o)}}d(R_{zo}e^{- i\theta  })=R_{zo} \int ^{\infty}_{-\infty}{\cfrac{h(z)}{(z-z_o)}d(e^{ -i\theta  }) }\)

which is unfortunately valid for any \(R\gt R_{zo}\).  Which leads us to strict \(R_{zo}\lt R\lt R_{zo}-\Delta R\).
...

All these suggest that with,

\(\int ^{\infty}_{-\infty}{ f(z)d(e^{- i\theta  }) }=F(\omega)\)

where \(\theta=\omega t\),

we have just extracted the argument part of the function \(f(z)\).

\(\cfrac{d F(w)}{d(e^{-i\theta})}=f(z)\)

put back the argument part of the function.