Complex Analysis: Jordan's Lemma

  Рет қаралды 21,104

qncubed3

qncubed3

4 жыл бұрын

Today, I present a proof for Jordan's lemma, a very useful result in complex analysis especially when calculating contour integrals. We use various estimations and inequalities to show that the value of the integral over a semicircular arc does indeed go to zero under certain conditions.

Пікірлер: 17
@academicstuff548
@academicstuff548 8 ай бұрын
Thanks for such brilliant videos.
@ravitejassu
@ravitejassu 4 жыл бұрын
Excellent explanation
@prabalbaishya6179
@prabalbaishya6179 3 жыл бұрын
Nice! Also I think we could have used the fact that the exponential decay function converges extremely rapidly and when it is with some arbitrary function (which doesn't diverge very badly for example like e^z²) the limit as the independent variable approaches ∞ is 0. Here in our proof we have f(z) which we have restricted to as a rational function and I think there is a theorem which states that we can apply the limit, even before evaluating the integral. So we see that whatever divergence the linear term 'R' and |f(z)| produces is killed by the strong convergence of the e^-(aRsint) and as t lies between 0 and π so sint is always >0. So we can conclude that as R gets bigger and bigger the integral goes to 0. I might have done some mistakes while explaining as I have just started out complex analysis. Also your videos are just awesome for me!
@jackmoffatt2499
@jackmoffatt2499 4 жыл бұрын
Really good and clear explanation. Much appreciated :)
@qncubed3
@qncubed3 4 жыл бұрын
Thanks! Glad you found it useful.
@jonahlehner3855
@jonahlehner3855 3 жыл бұрын
Amazing explanation
@user-wu8yq1rb9t
@user-wu8yq1rb9t 2 жыл бұрын
*Long time no see!!* *I'm waiting for your next video*
@lucasfranco1758
@lucasfranco1758 2 ай бұрын
Could you move the limit as R goes to infinity inside of the integral instead of using an inequality?
@shameer339
@shameer339 3 жыл бұрын
Channel Subscribed 😍😍😍
@jieunboy
@jieunboy Жыл бұрын
Amazing thx
@juniorcyans2988
@juniorcyans2988 7 ай бұрын
I wish you could have do some examples to show how to apply the theorem. That would be more helpful. Anyways, thank you very much!
@stringsam
@stringsam 4 жыл бұрын
good stuff :)
@qncubed3
@qncubed3 4 жыл бұрын
Thanks!
@abcdef2069
@abcdef2069 7 ай бұрын
at 18:35 what if a =0 then aR = undetermined, ....whenever you are integrating a big semi circle R....but most com integrals dont have exp(iaz)
@user-wu8yq1rb9t
@user-wu8yq1rb9t 2 жыл бұрын
Hello Dear *QN3* . I Have a request, please speak about *Bessel functions* too. Thank you
@fordtimelord8673
@fordtimelord8673 2 жыл бұрын
Subscribed
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