Tuesday, June 13, 2017

Chinese Remainder Theorem

I saw this example and i think i have understood how Chinese Remainder Theorem Works. First lets take three numbers which are relative prime $2,3$ and $5$. Lets try to find a number which gives the remainder $1,2$ and $3$ when divided by those 3 relative primes we chose. Lets write the original number are $x = 15x_1+10x_2+6x_3$ now the nice thing about this $x$ is when we divide by $\frac{x}{2} = \frac{15x_1}{2}=1$ and the smallest value which satisfies this equation is when $x_1 = 1$, Similarly $\frac{x}{3}=\frac{10x_2}{3}\Rightarrow x_2=2$ and $\frac{x}{5}=\frac{6x_3}{5} \Rightarrow x_3 =3$. Thus our number $x = 15x_1+10x_2+6x_3 = 15(1)+10(2)+6(3)=53$. Is this correct ? well this does satisfy the original condition of the remainders, however this is not the smallest number. If we multiply the original numbers we get $2*3*5=30$, now this divisible by all $2,3$ and $5$. So if we subtract the multiples of this number from any number the remainders will not change and hence we can obtain a smaller number which is $53-30=23$

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Saturday, May 20, 2017

Chinese restaurant in zone G bogota

I went there in March 2017and tried this vegetarian chopsuey

Zone G in Bogota

Zone G is near Calle 74 and next to 7. There are lots of good restaurants are there and one can savour different cuisines. On March 19 2017 I went to this artisan restaurant and tried this cheese macaroni and it was lovely.

Funza, Sai Baba School.

I been volunteering at this school for a while. Teaching kids Mathematics and it's a very fulfilling work. Today they celebrated teacher's day in a unique way. By tying strings.

Vegetarian tacos in Bogota

For about 20 mil pesos. That was a very full lunch.

Saturday, April 22, 2017

Kofta gheye ke

Amazing Kofta, rice, dal, mango chutney, gaurd subzi and parallel ki subzi. 

Zero water bill, Thanks Arvind Kejriwal

What a surprise to again receive zero water bill. AAP under Arvind Kejriwal is doing amazing job by getting rid of corruption a deal focusing on the core issue s of water, electricity, education, health and infrastructure. God bless them. 


I don't know when this was taken. But I think its right after Holi festival. Look at the big collars on that shirt. Epic!

Friday, April 21, 2017

Bhojpuri lakokti

My grandfather Rameshwar Prasad used to say this

Kose kose gor dhoye
Teen kos par khaye
Jahan jahan man karei
Tahan tahan jaye

The essence is if you wash your feet every mile and eat at every 3 miles then you can go anywhere you feel like. Because washing your feet refreshes you and eating reinvigorate you.
I always feel this is well said. 

Mohalla clinic in Kamla Nagar, Delhi

Arvind Kejriwal's mohalla clinic is a game changer.  I visited the clinic last week and talked to the people there and they seemed very satisfied with the work. The clinic is air conditioned and it was week stock. It has been opened for a month. It's impressive how much if a state government is willing can do for its citizen. I didn't take the camera that time. So today I went to get the picture.

Wednesday, April 19, 2017

Sperners Lemma

There are basically two lemmas in Topology which allow us to prove Sperner's Lemma.
Lemma:1 If a close interval [0,1] has finite number of points that divide it into smaller intervals by points either 0 and 1. Then there are odd number of intervals whose end points are different.
Proof: Think of the left most 1 out of all the one. This will form the very first interval of the type (0,1). The next interval if is present will be of type (1,0) and this forces the presence of another interval of type (0,1). So we see that the intervals of type (0,1) occurs at odd positions and since the last interval has to be of type (0,1). It means we will have odd number of intervals.

Lemma:2 Suppose any room of a house has 0,1 and 2 doors. Then the number of dead ends and the outer door have the same parity.
Proof: First thing to notice is that there is a unique path from any given door to another door. Second, there are only 3 such path exist.
1. Outer door to Outer door (let there be m such paths. For each path we have two doors, therefore we have 2m such outer doors).
2. Outer door to Dead end door (let there be n such paths. For each path we have one outer and one dead end door, therefore we have n outer and n dead end doors)
3. Dead end door to Another Dead end door. (let there be p such paths. For each path we have 2 dead end doors. Therefore we have 2p dead end doorss)
Number of outer doors = 2m+n
Number of dead end doorss = 2p+n
Thus both have same parity.

Sperners Lemma: It gaurantees the existence of a dead end triangle in any triangulation of a triangle obtained by the following method. The vertices are labelled 1,2 and 3. Then the side containing (1,2) vertex has only 1 and 2 intermediate point and so on. The vertices of triangle inside could be labeled by any of these three numbers.
Proof: Suppose (1,2) and (2,1) are the doors. Then by lemma 2 we have only doors on one side of the triangle and there will be odd number of these. So if we enter through any of the doors either we exit from another door then pairs are taken. So we will always be left by door which is not matched and that mean it will end up going into a triangle with all three different vertices.
Remark: There are only 2 types of triangle which allow a path (1,1,2), (2,2,1) and (1,2,3). All other triangles are inaccessible.

Following two videos explain sperners lemma and using fair division.

This gives a little more explanation to the above. Both complement each other.

Tuesday, April 18, 2017

Dal pakori

One of the best place to eat dal pakori is Kainchi dham near bhavali on the way to Ranikhet. Uttrakhand is my favorite travel destination in India. Amazing food and equally amazing people. The mountains and river in this state are of unparalleled beauty.

Breakfast in Delhi

A healthy start! 

Meeting Roopesh

Just came back after meeting Roopesh. Discussed lots of things ranging from participating in a company to starting a business. Its always good to catch up with good friends.

Selfie with Mummy

Here is a selfie with my mom

Shaking hands with Arvind Kejriwal

I am a big fan of Arvind Kejriwal.  He is the rare politician who does what he says.  To me he is bigger than Gandhi. He has brought tangible changes to the lives of the people and has shown what good intentions can do. So when I heard that he was coming to Kayla  Nagar.  I reached there and had the fortune of seeing him in person. Here are some photographs.

Childhood friends

It was great to see some of my childhood friends. Rajat,  Prateek and Rinkoo. I wish they could also see the amazing work being done by Arvind Kejriwal,  Manish Sisodia, Satyender Jain and Kapil Mishra.  Along with many selfless volunteers. Really proud of these people. 


Tuesday, March 07, 2017

Harmonic series without number 9 is convergent

There are tons of proofs that harmonic series diverges. What if we have a harmonic series where we get rid of all the numbers which contains $9$, will it still converge. For single digit there are $8$ numbers which do not contain number $9$. Single digit numbers $8$ Two digit numbers $8 \times 9 $ Three digit numbers $8 \times 9 \times 9 = 8\cdot 9^2$ 4 digit numbers $latex 8\cdot 9^3$ ... Also notice that largest fraction in harmonic series Two digits $\frac{1}{10}$ Three digits $\frac{1}{100}$ Four digits $\frac{1}{1000}$ So if we replace the terms of harmonic with these fractions we will get an upper bound on the harmonic series devoid of number $9$ It is $\frac{1}{1}\cdot 8+\frac{1}{10}\cdot 8 \cdot 9+\frac{1}{100}\cdot 8 \cdot 9^2+\cdots+..$ and $\Rightarrow 8\cdot \frac{1}{1}+8\cdot \frac{9}{10}+8\cdot \frac{9^2}{10^2}+8\cdot \frac{9^3}{10^3}+\cdots$ This is a geometric series and the sum is $\frac{8}{1-\frac{9}{10}} = 80$. Thus the geometric series with common ratio of $\frac{9}{10}$ is convergent.

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