Hacker News: harshavr

New comment by harshavr in "NASA finds water reservoir equivalent to 140 trillion times the world's oceans"

harshavr — Sun, 24 Jul 2011 07:10:20 +0000

I am no expert on this, but if you assume the cosmological principle which states that our universe is roughly isotropic, there is a natural set of observers called comoving observers who are at rest with respect to the expansion of the universe. One can define a universal time using the clocks of these observers. Presumably, this is what gives meaning to statements like the universe is 14 billion years old.

New comment by harshavr in "Economist's View: "The Mathematics Generation Gap""

harshavr — Tue, 31 May 2011 22:07:14 +0000

Not to minimize the importance of teaching, but the content is important too. Instead of the content consisting of memorizing and performing algorithms, hoping for students to discover meaningful patterns/concepts/insights or rely on teachers to provide them, maybe the content should be doing this explicitly. One topic in the high school syllabus which actually does this is Euclidean geometry, where everything is coherently derived from basic principles as opposed to a grabbag of techniques. Maybe, one could present arithmetic in the same way, not focussing on the how to do calculations but the patterns in these calculations and a few basic principles too discover/prove them. Alternatively, one could focus on applications of mathematical techniques in toy versions of real world problems.

Arithmetic algorithms still have value - for the insight they give on arithmetic and because following a complex algorithm is itself a skill with value.

But there is no need, as we do now, to insist on performing them so many times, or to do them very quickly in exams.

The main problem with this new approach, I feel, is that it makes learning mathematics harder. Building richer conceptual models which is necessary for both applications or theory is more interesting and meaningful, but also more difficult than following prescribed algorithms. It is harder to test in an exam, and where testable the problems are much harder.

This issue of algorithms vs conceptual understanding, is important at the undergrad level too. Eric Mazur has a nice video about this where he also talks about his way of testing conceptual understanding by asking very simple but illuminating questions - http://www.youtube.com/watch?v=WwslBPj8GgI

New comment by harshavr in "Levels of Infinity"

harshavr — Fri, 22 Apr 2011 22:46:32 +0000

Nice explanation, though I dont see how this leads you into becoming a formalist at the end. That countable models exist for the set theoretic universe, seems like part of the phenonmena of infinite structures having perfect reflections in subsets. This is, of course, much more breathtaking than the more usual facts like the natural numbers having the same cardinality as even numbers since cardinality is transcended and the whole universe collapses into a countable set.

New comment by harshavr in "Dynamic languages are static languages"

harshavr — Sun, 20 Mar 2011 20:34:39 +0000

Isn't this a property of the implementation rather than the language, though? Couldn't you have a compiler option to keep the type tags attached to the bits, sacrificing some of the speed benefits of static typing but keeping the primary advantage of proofs/testing?

New comment by harshavr in "The Truly Scary Part About Facebook Open Graph"

harshavr — Tue, 27 Apr 2010 21:28:48 +0000

If there is a real need, wont scraping toools with easy interfaces be developed by competitors to allow a user to get personal data out while migrating? Its the user's data after all. Lock-in due to the usefulness of friend info might still be significant, though.

New comment by harshavr in "This link says it's from YouTube but it's not"

harshavr — Mon, 12 Apr 2010 23:02:42 +0000

Some banks display a customer preselected image after the user name & before entering a password. This seems to be a good solution to phishing if one keeps the username private. Otherwise a site could give you the option of using two part passwords.

New comment by harshavr in "Ask HN: Is functional programming really worth it?"

harshavr — Sun, 14 Mar 2010 21:21:25 +0000

Before you arrive at a judgement of the paradigm itself be sure that you know some of the standard ways to solve problems in the field.

Some basic things which i didn't knew in the begining :

Fast persistent data structures - Coming from imperative langs, one might be hesitant to write functions which take a million elt vector, modify it and return a new vector. It is important to know that any good implementation of functional data structures will allow you to do this in constant time & speed. (independent of the size of the data structure).

Editor combinators : If you arent aware of this & are modifying a data structure with several levels of nesting, imperative assignment will seem much more convenient, ie dont translate foo.bar[8]=3, into something of this pattern barNew = editVector(foo.bar, 8, 3), fooNew=editMap(foo, "bar", barNew). It gets worse with more levels. Instead, use an editor-combinator library which will allow to you specify the path within the data-structure and a new value just as in the imperative case.

Things to know which are not strictly FP related, but nevertheless very useful - pattern matching simplifies definitions a lot, typeclasses are usually more convenient than class hierarchies.

Someone has already pointed out advice on libraries, (Clojure or any using any popular language in a functional way).

The main thing which motivates all of this - composability. It is hard to combine procedures with side effects into compound procedures because one needs to keep track of whether the component procedures are interfering with each other. FP eliminates this friction in composition.

New comment by harshavr in "Reflections on leaving Haskell"

harshavr — Sat, 13 Mar 2010 19:22:39 +0000

Can you clarify? I thought that keeping separate streams of side effects is not possible when one stream influences the other. The logging process depends on what actions happen in the IO sequence though not the other way around. Are you talking about keeping the normal IO actions in one monad, logging actions in another & then composing the two into an outer IO monad?

New comment by harshavr in "Why the Windows Registry sucks … technically"

harshavr — Fri, 19 Feb 2010 04:09:18 +0000

Since you can use gconftool shell command to get & set key values, it seems consistent with the unix philosophy. It is actually easier to use in a script than to parse a text file. For tree level operations, one can use the standard directory commmands like mv, cp inside the ~/.gconf directory. gconf-edit is a tool you use only if you want to. One could actually write a simple emacs mode for doing the same thing.

New comment by harshavr in ""Welcome to the Machine": State monads in Clojure"

harshavr — Wed, 10 Feb 2010 03:32:52 +0000

If I remember correctly, there was a more tricky problem in implementing monads without the type system - sometimes which monad is chosen for an expression, depends not just on the arguments, but the expected type of the result. Ex : "return 3" might be [3] or an IO action with result 3. The compiler decides this based on the surrounding context. In dynamical languages one would have to manually specify which kind of 'return' you mean.

This surrounding context inference feature, which is useful for type classes other than monads, has the unusual consequence that you need to specify more typeinfo in a dynamic language.

New comment by harshavr in "When work doesn't pay for the middle class"

harshavr — Wed, 20 Jan 2010 05:12:16 +0000

B) should be disincentive to save using money, not a general disincentive to save itself. One could make investments in any other commodity whose value relative to other commodities stays constant or increases.

It is a somewhat unusual tax, in that your tax rate is based on what proportion of your assets are in dollars. Does someone know what the rate per year on dollar assets is and how to calculate it? You would need to know how much money the Fed prints in a year. Do they publish it or was that what auditing the fed was about?

Also for A), banks probably factor in inflation while setting the interest rate for a loan. So, the relevant variable, i guess, is unexpected inflation rather than the value of inflation itself. The debtor benefits only when the loan market makes low estimates.

New comment by harshavr in "Portrait of a Noob"

harshavr — Wed, 23 Dec 2009 00:54:42 +0000

The first part seems to be motivating something like a macro system for comments. What if one abbreviated compound situations using a single word or a phrase along with a separate file with expansions of the abbreviations into more detail. So, one can comment at a more abstract level and still be understandable (using say, a tool which displays the expansion when hovering over the abbreviation, or a separate window with expansions of all the abbrevs used nearby). Ideally, of course, the abstraction would be captured in the code itself, and the expansion would be the comment before the function or the macro defining the abstraction. So this system will be useful only when there are abstractions in comments which are not reflected in the code.

Tyler Cowen on problems with story based understanding

harshavr — Fri, 20 Nov 2009 05:19:44 +0000

Article URL: http://tedxmidatlantic.com/live/#TylerCowen

Comments URL: https://news.ycombinator.com/item?id=951942

Points: 1

# Comments: 0

New comment by harshavr in "Global warming: Moral vs Economic solutions"

harshavr — Sun, 25 Oct 2009 19:56:17 +0000

I wonder if there is a special advantage for geoenginnering solutions like carbon sequestration where instead of perturbing a complex system and using technology to individually manage all the negative consequences, we use technology directly on the variable we are influencing. It frees us from calculating all the consequences.

New comment by harshavr in "The Anatomy of Determination"

harshavr — Sun, 06 Sep 2009 06:51:51 +0000

well, best of you luck! hope any possible bad phases dont get to you.

New comment by harshavr in "Burn Baby Burn"

harshavr — Sun, 06 Sep 2009 02:28:00 +0000

1 is a real issue right now. But, this will change. Once there are enough users, students/philantropists/governments might pool up money to pay good universites/professors to put up videos & other material for free online. There is scope for a website which would keep track of requests & payments for a particular course.

New comment by harshavr in "The Anatomy of Determination"

harshavr — Sat, 05 Sep 2009 23:24:05 +0000

As a grad student in math, i would say that determination still plays a important role. For me, there have often been periods where you lose motivation and dont see why you are doing what you are doing, and then sometimes there are moments of clarity. (someone aptly compared this to mountain climbing). I imagine this happens in lots of other fields,(music, to pick a random example) where there is a prequisite of learning lots of arbitary things before understanding/creativity happens. Determination, is what you might need to to go through these phases.

New comment by harshavr in "Ask HN: SICP says "Program == Language Evaluator" What does this mean?"

harshavr — Sun, 09 Aug 2009 13:15:26 +0000

The user of the web app has a model and a desired result in mind and somehow needs to communicate this intention to the system. Viewed this way, it is clear that there must be a language in which this communication happens. Of course, we call this the interface. A user interface can be thought of as very high-level, very domain-specific language.

New comment by harshavr in "Nissan unveils world's first mass-market electric car, the Leaf"

harshavr — Mon, 03 Aug 2009 04:44:11 +0000

"gas tank is equivalent to ~0.5megawatts", just to be more clear, could you say how many hours of driving are you assuming the gas fill will last, since your measurement is in terms of power?

New comment by harshavr in "Bird Navigation Breaks Entanglement Record"

harshavr — Fri, 03 Jul 2009 19:39:30 +0000

Here's an attempt at distinguishing a truly quantum effect: can the same thing happen in a universe with classical physical laws and also keeping the other relevant variables fixed?(the latter part is important because the classical universe is, of course, turing complete).

Also, there is a similar programming qn. Suppose you have a program P running on a machine Q, and the api for a machine C is implemented on Q, so that programs for C can be run on Q. How do we actually figure out if P is really a C program running on Q?