Zeros and Poles | Removable Singularity | Complex Analysis #7

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Everything you need to know about Zeros, Poles and Removable Singularity. The video also includes a lot of examples for each concept.

LINK TO COMPLEX ANALYSIS PLAYLIST

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Consider subscribing, liking or leaving a comment, if you enjoyed the video or if it helped you understand the subject. It really helps me a lot.

IMPORTANT LINKS

CONCEPTS FROM THE VIDEO
► Zeros
Also known as "roots" to an analytic function. A point z_0 in the complex plane is a zero of order n for some analytic function f(z) if:

f(z_0) = f'(z_0) = f''(z_0) = ... = f^(n-1) (z_0) = 0 and f^(n) (z_0) =\= 0.

An alternative definition is that f(z) has a zero of order n at z_0 only if it can be rewritten as

f(z) = (z-z_0)^n * g(z), where g(z_0) =\= 0

► Poles
A pole is a specific kind of singularity of a complex function, it behaves as the singularity of 1/z^n at z = 0. So the most intuitive definition is that poles are points z_0 in the complex plane so that f(z_0) = g(z_0)/0, where g(z_0) =\= 0.

But the more formal definition is that a point z_0 in the complex plane is a pole of order n for some analytic function f(z) if:

lim_(as z goes to z_0) of (z - z_0)^n * f(z) =\= 0

A pole of order one is called a simple pole and if we only observe the neighborhood around z_0 when the relation above take the following form

f(z) = g(z) / (z-z_0)^n, where g(z_0) =\= 0

► Removable Singularity
A removable singularity is a point at which the function is undefined, but it is possible to redefine the function at that point in such a way that the resulting function is regular in a neighborhood of that point.

EDITS:
The 2:nd derivative at 03:20 is wrong, it should be g''(z) = 2, however does not change the order of the zero since g''(-4) =/= 0.

Missed "-" at 04:00, since the derivative of cos(z) is -sin(z).

TIMESTAMPS
00:00 - 00:11 Intro
00:11 - 00:52 Definition Zeros
00:52 - 02:40 Definition Poles
Example Zeros:
1) z-1 02:40 - 03:09
2) (z+4)^2 03:09 - 03:51
3) cos(z*pi/2) 03:51 - 04:13
4) (z-1)cos(z*pi/2) 04:13 - 04:40
Example Poles:
1) 1/(z-1) 04:40 - 05:35
2) 2/(z+3)^2 05:35 - 06:39
Zero and Pole at the same point: 06:39 - 07:51
Definition Removable Singularity: 07:51 - 08:15
Example Removable Singularity:
1) ((z-1)(z+2))/((z-1)(z+3)^2(z+1)) 08:15 - 08:55
2) sin(z)/z^3 08:55 - 10:04

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Is 2nd derivative of g(z)= (z+4)^2 is correct ?

WildlifeAlive
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You have no idea how helpful your complex analysis playlist is for me. ❤❤❤

blzKrg
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Overall wonderful work here, I'am studying Complex analysis as my last year of bachelor and it's a really nice condensed playlist to study, the fact you add example and solutions is really a plus.

scampx
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PunmasterSTP
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MIND=BLOWN

diegonavia
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yongjoonkim
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4:53 I am over 18 years old and I am shitting my pans just thinking about it!

francribaj
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Thanks :) that's really helpful. PS: your voice is extremely soothing

PS
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Excellent video I came here in search for the pole and zero at same time case . I am not able to find about it at any place . Finally my search ended at this video . Thanks for explaining in such a beautiful manner . Really appreciated.

psiphizone
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Thanx sir really helpful . I pray that u may lead to the right paath so u may be successful hereafter

izyyzlkhan
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Cramming all of your videos of complex analysis for my final tomorrow wish me luck.

josecastro
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Your teaching skills are very good
Keep it up

govind
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You, my sir, are what would be generally known as a Legend.

athul
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Need permission to acces canvas on drive :( Thx for your amazing videos, its helps me a lot to understand this topics. You are amazing!!!

guidoperez
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this is so understandable compared to my textbook.Thanks a lot!

bjRiis
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9:07 Why is that z=-2 not a pole then?

Amani_Rose
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Thanks for your work! It's very helpful.
I have 2 simple questions and will be happy to get an answer :)

1) Why we don't investigate z=-2 in 1 example? It is a zero of order 1 then, right?
2) What is the other option possible except of rewriting sin z (in 9:40 you said it's not necessary)?

Best wishes,
Myro

myroslavaa_
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I love your lectures man. Keep posting more maths content <3

nopecharon
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would someone please help me. If for example in 2.) of determining pole and its order the second limit is still 0 or infinity, do we need to raise the denominator again, but this time to the power of 3?

lordyabo
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Nice explanation sir. Thank you so much. Keep going sir

Elaya_bharath_V_T