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alxv

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Python 3.4 Beta 1 Released

python.org

89 pointsby alxv13 yıl önce28 comments

Twitter reschedules downtime in response to Iran situation

blog.twitter.com

2 pointsby alxv17 yıl önce0 comments

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8 yıl öncediscuss

The 35mm format is rather amazing balance of design trade-offs. No wonder it is so enduring.

It's large enough for the double-Gauss lens (a.k.a. normal prime lens) to have a nice shallow deep of field wide open. f/1.2 is close to the limit of a typical SLR mount. So a normal 50mm f/1.2 lens gets us 42mm of aperture. This means we can get the same depth of field and angle of view as a 6x7 medium format with a 110mm f/2.8 lens or a 4x5 large format with a 180mm f/4.5 (but with a much smaller system!) And we get a faster lens as a bonus.

Smaller formats lose some of that versatility of composition. The focal length of the normal lens on APS-C is 32mm. We would need f/0.8 lens to the same DOF. That's not possible on an SLR mount. Mirrorless systems with their shorter flange distances could get us there. But even then there are limits to how short the flange can be because image sensors become much less efficient as the angle of incidence of the light hitting them increases.

9 yıl öncediscuss

You only need 2 processors, since each cores gives you 2 vCPUs. "For the n1 series of machine types, a virtual CPU is implemented as a single hardware hyper-thread" --https://cloud.google.com/compute/docs/machine-types

9 yıl öncediscuss

You are missing a crucial piece here to have consistent hashing: you also need hash the names of the servers. With consistent hashing you hash both the names of the requests and of the servers, then you assign the request to the server with closest hash (under the modulus). With this scheme, you only need to remap 1/n of the keys (where n is the number of servers).

9 yıl öncediscuss

There is a proof shown in this handout: https://people.eecs.berkeley.edu/~sinclair/cs271/n15.pdf

It's hard to understand why this technique works so well without digging deep in the math. Roughly speaking, if you throw n balls in n bins at random, the maximum of number balls in any bins will grow surprisingly quickly (because of the birthday paradox). However, if we allow ourselves to choose between two random bins instead of one, and put the ball in the one with the fewest balls in it, the maximum number of balls in any bins grow much more slowly (i.e., O(ln ln n)). Hence, having that one extra random choice allows us to get surprisingly close to the optimal approach of comparing all bins (which would give us O(1)), without doing all that work.

9 yıl öncediscuss

The method is called "Power of Two Random Choices" (http://www.eecs.harvard.edu/~michaelm/postscripts/handbook20...). And the two-choices paradigm is widely applicable beyond load balancing. In particular, it applies to hash table design (e.g. cuckoo hashing) and cache eviction schemes (https://danluu.com/2choices-eviction/).

9 yıl öncediscuss

What happens when the number of servers changes? The cache hit rate would likely drop to zero until it warms up again, which is a good way to accidentally overload your systems.

Load balancing based on consistent hashing is the better way to implement this.

10 yıl öncediscuss

If your employer 401k plan allows it, you can roll over after-tax 401k contributions to a Roth IRA (a.k.a. mega-backdoor Roth IRA).

10 yıl öncediscuss

Sorry, it turns that was misunderstanding from my part. It turns out we cannot solve a board row by row without revisiting the previous rows. The board below is a counterexample:

  101
  010
  100

The first and second rows are solved. However we cannot solve the last row without re-doing the first and second rows. The two solutions of this board shows this:

  solution #1:
  110
  100
  000

  solution #2:
  110
  110
  000

Actually, seeing my mistake made me challenge my assumption that a singular matrix over the reals might not be over integers modulo 2. This is likely wrong too. I don't know much about abstract algebra (and I am not a mathematician). Wikipedia (https://en.wikipedia.org/wiki/Determinant#Square_matrices_ov...) states "the reduction modulo m of the determinant of such a matrix is equal to the determinant of the matrix reduced modulo m."

The move matrix M for all boards of size 3n + 2 appears to be singular. This means these boards may have no solution or a large number of solutions.

10 yıl öncediscuss

For every boards are two chessboard patterns we can solve for. For example, for a 3x3 board we can have:

  101        010
  010   or   101
  101        010

where 1 is a white square and 0 is a black square.

We can represent any N×N board as a N² vector. So, we can represent one of the chessboard pattern as:

  010
  101 = 010101010 = y
  010

At the beginning of the game, the board is at some random initial pattern.

  110
  111 = 110111010 = y0
  010

The goal of the game is to find the necessary moves to form the chessboard pattern. Hence, we want to solve the equation

  (y - y0) = Mx

where M is a N²×N² matrix representing the effect of every possible moves. Pressing on a tile is equation to addition by 1 modulo 2.

  1 + 1 = 0 (mod 2)
  0 + 1 = 1 (mod 2)

For example, pressing the top left tile is the same as adding this effect vector to the board vector:

110110000

If we do this for all 9 tiles of the 3x3 board, we find the matrix M to be:

  110110000
  111111000
  011011000
  110110110
  111111111 = M
  011011011
  000110110
  000111111
  000011011

where the i-th row is the effect of pressing the i-th tile. Now, we can just solve for x (assuming M is not singular). Re-using our above example, we find

  (y - y0) = Mx
  (010101010 - 110111010) = Mx
  100010000 = Mx
  111100100 = x   (by Gaussian elimination)

This means we can press the following tiles (in any order) on the board to solve it:

  111
  100
  100

If you are interested, I wrote some quick demo code that shows how this could be implemented in Python: https://gist.github.com/avassalotti/7452318c9e9b8dec637bc7c0...

10 yıl öncediscuss

Like Lights Out, this game can be solved using Gaussian elimination over Z/2 (integers modulo 2). This means the order of the tiles you press do not matter, and that you can solve the board by forming the desired pattern row by row.

10 yıl öncediscuss

During the winter, most fresh vegetables in Canada are imported from Mexico and the US. These are mostly breed for shelf life and usually bland. In the summer, local fruit and vegetable can be quite tasty if you know where to shop. The public markets of Montreal are very good (http://www.marchespublics-mtl.com/). You can also subscribe to get weekly organic baskets from local farms during the harvest season (http://www.paniersbio.org/en/).

10 yıl öncediscuss

On the other hand, the bland stuff doesn't poison you as much with lead.

http://www.environmentalhealthnews.org/ehs/news/lead-in-vine...

10 yıl öncediscuss

In the U.S., Californian olive oils are your best bet. Otherwise, Costco Kirkland Signature olive oil (which is now Greek oil [1]) is another good choice.

Outside of Italy, it's difficult to find Italian olive oils that are not blended. The 2014 and 2015 harvest seasons have been terrible due a bacterial blight [2] that crippled many olive farms in Southern Italy.

[1] http://www.seattletimes.com/business/retail/costco-embraces-...

[2] https://en.wikipedia.org/wiki/Xylella_fastidiosa

11 yıl öncediscuss

Previous discussion: https://news.ycombinator.com/item?id=10330280

11 yıl öncediscuss

"Don't be evil" is still included in Google's code of conduct.

https://investor.google.com/corporate/google-code-of-conduct...

11 yıl öncediscuss

There is a very succinct implementation of Algorithm X in Python that uses a variation of the Dancing Links approach.

http://www.cs.mcgill.ca/~aassaf9/python/algorithm_x.html

http://www.cs.mcgill.ca/~aassaf9/python/sudoku.txt

11 yıl öncediscuss

Google runs a company-wide disaster recovery testing event every year. Earthquakes are among the numerous scenarios simulated.

https://queue.acm.org/detail.cfm?id=2371516

11 yıl öncediscuss

That's with resources cached. HTTP Status 304 means the resource was not modified, and thus can be retrieved from the local cache.

11 yıl öncediscuss

A/A tests (also known as Null tests) are useful to validate that users are assigned to the control and experiment groups without bias.

Offline resampling methods, like bootstrapping, are better if you're looking to robustly estimate the variance of the experiment.

12 yıl öncediscuss

You can read the article if you come from a Google search.

http://www.google.com/url?q=http%3A%2F%2Fwww.medscape.com%2F...