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4:43 AM
@ManeeshNarayanan :)
$1749$
sorry , 1759
 
 
1 hour later…
6:13 AM
yesterday it was 1729
I multiplied $B(\lambda)$ with $A-\lambda I$
I got $(B_0 A+B_1 A\lambda +...+B_r A\lambda^r) -(\lambda B_0+B_1\lambda^2+...+B_r \lambda^{r+1})$
How this term is zero?
@PrithiviRaj
@BAYMAX
@vidyarthi
That term can be further simplified as $B_0 A+\lambda(B_1 A-B_0)+\lambda^2(B_2A-B_1)+...+\lambda^r(B_rA-B_{r-1})-B_r\lambda^{r+1}$
which can written as the form given in the picture.
 
6:35 AM
Let me think .
 
okay.
me too. at my free time.
 
First of all $ det(C)=0$
 
why?
here we need to prove $C=0$
 
$|A-\lambda I|=0$
 
not given
:(
 
6:39 AM
but the determinant for characteristic matrix is always zero.
 
but $\lambda$ is not characteristic value
 
oh , fine
 
okay
is there any hidden hint that $\lambda$ is eigen value?
 
I am finding that , It should be
can you upload the page no 340?
 
but nothing is useful in 340
 
6:49 AM
this is a corollary of Cayley-Hamilton Theorem , and there $(A-\lambda I)$ stands for characteristic polynomial.Right?
 
not corrollary. lemma
 
Ok , this is a theorem itself , we have to think something else.
 
this is the useful result for proving cayley hamilton theorem.
 
@ManeeshNarayanan the given sum $B(\lambda)(A-\lambdaI)$ when exapnded is clearly seen to be telescoping, thus summing to zero
 
not getting.
where is the mistake in my exapansion.
 
6:56 AM
 
@PrithiviRaj @vidyarthi just above it.
 
@ManeeshNarayanan what do you mean?
 
I expanded just above the conversation. but not getting zero.
is there any mistake in my expansion?
nothing is cancelling in my expansion.
 
@vidyarthi there , $\lambda $ is supposed to be an eigenvalue and$|\lambda I- A|$ is stated as the product of Eigen values of $(\lambda I -A)$.
 
@ManeeshNarayanan yes, the expansion is right. The sum telescopes when $\lambda$ is an eigenvalue, and not otherwise
 
7:07 AM
but here I need to prove for arbitrary $\lambda$
right?
 
@ManeeshNarayanan the expansion is valid for arbitrary $ lambda$. Substitute $A$ in the place of $\lambda$ to get the cayley hamilton theorem
 
this is the lemma. we need to prove cayley hamilton theorem from this lemma.
 
@ManeeshNarayanan , now I realized why you have said that . Taxi no. of GH Hardy , Ramanujan ?? Right? Sorry , for changing the topic.
 
the lemma is true only for $\lambda$ being an eigenvalue, otherwise, we can clearly see some terms remaining in theexpansion
@ManeeshNarayanan which book is that?
 
A survey of Modern Algebra.
Birkoff
 
7:15 AM
@ManeeshNarayanan what is the next page?
 
okay. I will upload.
 
I mean, just below this lemma. How have they proved the theorem
 
@ManeeshNarayanan the main part of lemma is that $C$ is a matrix of constants. There lies the hint to proof
 
what that means?there is no $\lambda$ terms there. Right?
 
7:25 AM
yes, exactly
 
so $C=B_0 A$ right?
some thing there. let me think.
 
no, since $C$, being a constant matrix, equals a sum of matrices with some powers of $\lambda$, we should have each of $B_r=O$
 
so $B_0=O$ ?
 
yes
 
@vidyarthi , since each B contains $\lambda$'s in itself ?
 
7:34 AM
@PrithiviRaj no, $B_0$ is a matrix of constants
 
$B_k A-B_{k-1}$, $1\leq k\leq r$ also $B_r=0$, inorder to become $C$ is a matrix of contants. right
?
 
yes
 
so $B(\lambda)=0$
 
yes
 
Hence $C=0$
 
7:37 AM
yes, that is what is given
 
This theorem is strange for me.
 
even to me. Though it seems obvious, its proof is not. The main problem why the theorem seems strange is because multiplication of matrices, in general, is not commutative
 
I've concluded that $C$ will be a matrix of constants i.e. $C=O$ , if $B (\lambda)=O$ .
Is it correct?
 
that is why, the theorem is proved by using such lemmas. For otherwise, consider this proof: since $p(\lambda)=|A-\lambdaI|$ is the characteristic polynomial, then, by substituting $A$ in place of $\lambda$, we obtain $p(A)=|A-AI| =0$. But, the proof is wrong, because the lack of commutativity of matrices
 
@vidyarthi. but they assume $B_r \neq O$.
 
7:43 AM
still struggling with that proof...
 
@PrithiviRaj yes, true
@ManeeshNarayanan yes, $B_r\neq O$ unless $B(\lambda)=O$, which is the case here.
 
what does that mean?
 
if $B(\lambda) \ne O$ , then $B_r \ne O$.
??
 
okay
i am weak in english. but like to read math language than english language :)
 
me too , but it doesn't matter .
feel the feelings , :)
 
7:53 AM
@vidyarthi we have given $C$ is a matrix of constants. we proved $B(\lambda)=0$ equating all coefficients of $\lambda$ equals 0
then why did they assume like that?
 
8:14 AM
@ManeeshNarayanan sorry, not all $B_i$ are necessarily zero by assumption, but $B_r=O$ definitely which in turn implies $B(\lambda)=O$, which implies $C=O$
 
@ManeeshNarayanan I couldn't get the doubt?
 
@PrithiviRaj hello, IITB has released the answer keys for JAM 2018. Have you checked your real marks now?
 
then why did they write the $B_r\ne O$ unless $B(\lambda)=0$.
?
@BAYMAX What happens if $B_r\ne O$?
how $C$ is zero?
in that case.
 
hm..can u please upload pg 342
@ManeeshNarayanan
 
@ManeeshNarayanan look, if $B_r\neq O$, then $C$ must contain powers of $\lamba$, that is, it should be not be constant matrix
 
8:23 AM
okay.
@vidyarthi @BAYMAX see just aboove this message
 
@ManeeshNarayanan the proof can be said to be like proof by contradiction
 
@vidyarthi , yes it is 31.03 .
 
okay
@PrithiviRaj according to previous statistics, you will get under 300 rank.
 
Really !
 
@PrithiviRaj so you see the changes in marks from dips academy result!
 
8:33 AM
yes ,
now , my 2 msq's are correct.
and 1 nat
(more)
 
@vidyarthi How it is a proof by contradiction? then it should start like this $C\ne O$
 
@PrithiviRaj but it all depends on rank. If all perform poorly, then rank may go up. I all perform well, then rank goes down. So, just wait for final result, when things will become clear.
 
@vidyarthi okay! let us wait till 20 march.
 
@vidyarthi u r right.
@vidyarthi Have u checked the gate score?
Hai @BAYMAX
 
@ManeeshNarayanan the proof starts with $B(\lamba)\neq O$ and then ends with $B(\lambda)= O$
yes checked the marks. I may get around 40
@ManeeshNarayanan made several silly mistakes
 
8:40 AM
@ManeeshNarayanan , because $B_r \ne O$ until or unless $B(\lambda)=O$ , it shows that it is a proof by contradiction.
 
okay. mine is only 36. me too.
 
@ManeeshNarayanan actually statistics questions are on the same level or easier than JAM Mathematical Statistics paper
 
i didn't try stati.
 
did you get all functional analysis questions?
 
nope. i didn't attempt.
 
8:44 AM
i tried but did not get in exam, but now i see those were actually easy
 
liner, real, vector calculus,complex
okay
 
consider this question: let $T$ be the linear functional from $L^2$ given by $\int_{1/4}^{3/4}3\sqrt{2}f d\mu$ where $\mu$ be lebesgue measure. Then, norm of $T$ is?
 
let me check.
 
@PrithiviRaj didnt you give Mathematical Statistics paper?
 
no ,
I couldn't because I've studied mathematics and physics as major subjects in my B.Sc.
:43091533
I've to go now , bye! all
 
8:55 AM
@PrithiviRaj then you could have given physics paper, anyways, bye
 
Sry@ManeeshNarayanan I will get to u vry soon
 
it's okay.
@vidyarthi $|T(f)|\leq 3\sqrt{2}\int_{1/4}^{3/4}|f|d\mu$
right?
but what is the norm of $f$?
 
9:13 AM
@ManeeshNarayanan right. Norm of $T$ is defined as $\sup\frac{\|Tf\|}{\|f\}$
 
how would you define ||f||?
 
$\|f\|$ is the usual $L^2$ norm, given by $(\int f^2 d \mu )^{1/2}$
 
9:52 AM
I have no idea.
then
can yu please ask in the main site with ur try?
please share the link here.
 
it is quite easy. We have $\|Tf\|\leq3\sqrt{2}(int_{1/4}^{3/4})^{1/2}d\mu\|f\|=3\|f\|$ from which $\|T\|=\sup\frac{\|Tf\|}{\|f\|}=3$ quite simple, isnt it?
@ManeeshNarayanan
 
yes :'(
missed it.
@vidyarthi
 
10:09 AM
and this was a 2-mark question in Numerical Answer type
@ManeeshNarayanan how about this:$x^4+4$ is reducible or irreducible in $\mathbb{Q}[x]$?
 
irreducible
that also, i haven't marked
 
again the same mistake that i comitted- it is reducible
 
how?
roots are complex.
@vidyarthi
 
10:25 AM
@ManeeshNarayanan roots are not required for reducibility
 
yeah.
i think root test is applicable till degree 3. you are right.
actually. I studies the 3 years ago. I am bad in algebra :(
@vidyarthi
 
$x^4+4=(x^2+2+2x)(x^2+2-2x)$ Use sophie-germain identity
 
you are good in algebra than me. can you suggest some books?I have gone through gallian and hernstein.
was not interesting.
theorem, theorem,...$\infty$ :)
I just want to learn motivations and concepts.
@vidyarthi
 
@ManeeshNarayanan I may not be good at algebra. Anyways, I can suggest books. Try Dummit-Foote, Artin, Lang, Chatterjee, Nagpal and Bhattacharya
 
okay.
UFD and related things. I understood the purpse recently.
 
10:33 AM
yes, these books are good and classic. For guides, try beachy-blair, robert ash
 
okay. thank you very much.
 
and also hoffmann-kunze for linear algebra
 
i am fine at linear algebra
bad at abstract.
@vidyarthi
see you later.
 
@ManeeshNarayanan ok bye
 
 
4 hours later…
2:09 PM
@vidyarthi , haha I don't have interest in Physics. Or I can say I'm not good at Physics.
 
¯_(ツ)_/¯
nice symbol.
copied from maths chat group.
 
2:29 PM
@BAYMAX
Our group has frozen :'(
RIP
Who can give better advices?
How to make this kind of questions as routine type questions?
give references.
can I ask this kind of questions in main site?
 
2:44 PM
@ManeeshNarayanan beyond my thinking
 
in Mathematics, 9 mins ago, by Maneesh Narayanan
can you help me? not solving questions. How to improve myself to solve this kind of problems.https://www.isical.ac.in/~admission/IsiAdmission2017/PreviousQuestion/J‌​RF-Math-MTA-2017.pdf @BalarkaSen
 
3:28 PM
Sorry@ManeeshNarayanan
I see this is a nice group, sorry i could not practice
with u all
 
it's okay.
 
some times
I will
do it from now
 
yes. I got that.
by diagonalizing.
right?
 
3:30 PM
hmm
so which1 we should discuss
when is this exam?
 
actually, put this QP here. inorder to know which textbook shall I follow.
May
first week
 
I see
QP?
 
Question Paper.
 
you pasted the link?
here no?
 
3:35 PM
@ManeeshNarayanan i did not get this?
$v_{n+1} = A^n v_{1}$
so what can we say next?
 
I wish to prepare for the test.
 
so in order for $\lim_{n \rightarrow \infty}$ to exist
$\lim_{n \rightarrow \infty} A^n$ must exist?
first row of $A^n$ has $(2/3)^n + (1/3)^n$ , $2 . (2)/3^n$
 
okay.sorry
diagonalize A
so what will we get
A=X^tDX
okay
sorry
I forgot the formula.
 
$A =XdX^-1$
 
this will reduce the calculation of powers.
am I right?
 
3:43 PM
I think yes
so we get $A^n = X D^n X^-1$
 
Are the eigenvalues of $A$ distinct>
 
yes
am I right?
 
Yo
evalues are 1 , 1/3
And since distinct they are diagonalizable
 
3:48 PM
If i am correct, what is $X$
 
$v_{n+1} = A^n v_{1}$
 
I think column containing the eigenvalues?
 
eigen vectors
not values
 
Sorry
 
$Ax_1=x_1$
$Ax_2=1/3 x_2$
then $X=[x_1 x_2]$
 
3:49 PM
sorry
$x_{1} = [1,1]^T$
 
x_2??
I have done 6 months ago.
let me find.
 
$[1,-1]^T$
I guess?
 
So $D = diag(2/3 , 2/3)$
 
$v_{n+1} = XD^nX^T v_{1}$
nope
main diagonal must be containing eigen values
$D=diag(1, 1/3)$
check
 
3:53 PM
Sorry
yUP
so $lim_{n \rightarrow \infty}$
 
Y sorry???please don't say like that
 
only the first element of $D$ will survive?
 
I am also a student.
 
ok
 
let me check
I got limit as (a+b,a+b)
some thing went wrong.
 
3:58 PM
$D^n$ as $n \rightarrow \infty?$
$X ^ -1?$
 
take limit after multiplying X and X^-
 
Why after multiplying why not before multiplying?
I am poor in writing matrices
darn
 
for that we need to know about continuity
 
not just continuity
uniform continuity
:)
 
i for got all the theory
 
4:03 PM
Its apotential question
we should dig a bit more?
 
Yes. I will be back after dinner.
I will be back.
 
Sure
 
think!I will also think.
 
ok
 
4:24 PM
back.
 
Me too :)
Do u get $a+b$?
Hint - the factor $1/2$ comes from the inverse part
 
okay.
then my answer is correct.
yeah
 
nice
 
:)
Let's try Q4
 
rank 1?
speciality?
 
4:33 PM
Let $X$ be an $ n×n$ complex matrix of rank $1$ and $I $the $n×n$ identity
matrix. Show that
$det(I + X) = 1 + tr(X)$,
where tr(X) denotes the trace of X and det(X) denotes the determinant
of X.
yes
then eigen values TrX,0,0,...,0 right?
Enough to prove this. Right?
Rank 1 matrix is similar to $E_{11}$ right?
no no. sorry.
 
Hmm
But we have to think whats special in rank1 amtrix
i remember that rank1 matrices are special
they have some nice properties
if we know that then we can break the problem to much simple1
 
okay.
I was lying on the floor :).
very hot climate.
 
4:49 PM
nice, I also wnt sm sleep, sleep is contagious :)
 
thinking about the properties.
 
i had read some months backk about rank1 matrix
ASearch them
They are important
 
can you give the materials?
reference.
 
2
Q: What properties does a rank one matrix have?

MatthewMy question is what properties does a rank one matrix have? I saw a lot of papers mentioning that the matrix is rank one and so on. I know rank one of a matrix means that there are no independent columns or rows in that matrix.

 
thank you. How does this solve the problem here?
 
4:53 PM
u think i think
 
I have small doubts regarding the teaching. I know my lectures are utter boring. my students ask short cuts to pass the exam. I am sincerely doing my work. they are complaining me. I told them that I was ready to help to clear their doubts.
 
hmm
 
still they are asking shortcuts to pass the exam.
I really fed up with lecturing.
 
hm
 
I explain the geometric nature of gradients etc.
they are not listening.
they want only previous year paper analysis.
Am I doing wrong?
 
4:57 PM
try questioning them
like dnt just say the answer
extract it from them
this will make thm think about the concept
and hence brings concentration
like "lets take x>0"
rather ask then "can i take x<0"
yes thn why
no thn why
and tell tht questions will be hard in exam
ths will make them serious
 
I conduct exam every week. based on kreyzig excercise. they fail. they are not asking single doubts :'(
 
and give thm as assignments from different books they cant predict
u should find a way to motivate\
 
I gave assignments 60 questions to do . they were not submitting.
I advise them daily to ask doubts. they are not asking.
few are asking.
one or two girls.
I motivate them by narrating the biographies of scientists.
leave that. let's back to rank 1 matrix.
@BAYMAX
sorry for sharing my sad story.
come to Q4 @BAYMAX
let's try again.
bye. I am going to sleep. let's try tommorow.
 
5:18 PM
would mathematicians feel the usual society is like a wasteland?
It's like it's rare to find a person in a usual social setting who is conversed with math.
 
5:37 PM
what is gauge theory moduli space?
 

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