Do you know of any research about the accuracy of forecasts as a function of sensor data input? I.e. what kind of an improvement will we see if some number of Android users install PressureNet?

Here is a recently published paper by Cliff Mass that is the first attempt at forecast experiments with smartphone pressure data: http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-13-00188...

The early results are good. There will be an improvement [1]. How much of an improvement? We don't know yet. Cliff thinks it could be a revolution for some types of forecasts, but we don't have the density of sensors yet to know for sure.

For some comparisons, we sent cliff about 20,000 measurements per hour for his experiment in that paper. We're now delivering about 200,000 per hour to researchers, and that's not nearly enough. Our aim is for 2M per hour and I hope to reach that in the next 2-3 months. Around 1-2M per hour is probably sufficient to provide the "revolution" in accuracy that Cliff predicting.

I should also note that 1-2M per hour is small. We should be able to get closer to 1B per hour, but it'll take a while to ramp up to that kind of scale (that'll be like, every smartphone + watch + car that has a barometer).

The improvements will be slow and steady until we get massive scale and are able to run our models in real time. Until then, it's tough to guess how good the improvements will be.

[1] In the linked paper above, I believe the results were a reduction in root mean square error of about 1deg C for a 3-hour temperature forecast in the Pacific Northwest.

Note that your code still forces python to read the entire file! If all you want is the last line of a file, use the UNIX tail:

  tail -n 1 $f

Tail seeks backwards so it will only read the one line. Of course, this won't give you a line count.

EDIT: I haven't tested it but you might be interested in this implementation of tail in python: http://stackoverflow.com/a/136368

I've done timing tests and it is typically on par with tail & wc. The bulk of the time is wasted reading your file into ram, the time it takes to count the lines is essentially 0.

Edit: Of course I misspoke, yes tail is much faster for getting the last line of the file! I meant for getting the line count the loop methods is typically just ~5% slower than wc on sufficiently large files.

> There may be a market opportunity for an economist to write a big Piketty-style book on climate change.

Yale economist Bill Nordhaus' Climate Casino is that book. And his research with integrated assessment models concluded:

> The consequences of [climate change] will be costly for human societies and grave for many unmanaged earth systems; the balance of risks indicates that immediate action should be taken to slow and eventually halt emissions of CO2 and other greenhouse gases.

And, by the way, this analysis doesn't even take into account tipping points!

Until we as a society face the fact that doing something about climate change required compensating the owners of fossil fuels for not letting them extract them then we are going to get nowhere.

Why would we need to compensate them (Saudi Arabia, Venezuela and other owners) when it's our demand that gives them the ability to sell their product. Since the value of their oil reserves is tens (if not a hundred+) trillion dollars.. it would be cheaper to simply give everyone in the US and Europe a free electric car.

Edit: 100 trillion is so much money.. that we could literally replace every car in the entire world (1 billion cars) with a free tesla and still have money left over.

Yes the money involved is massive, but the way politics works is those with something to lose have far more power than those that will gain from any change. This is why tax reform is so difficult. The owners of all the fossil fuels are effectively able to veto all change unless we pay them off. If this is the case lets get on with buying them off.

I'm willing to face any fact that is true, but which owners in particular must be compensated, and why?

What is your specific critique of the carbon tax that the book proposes?

The reason why we need to compensate the owners of the fossil fuels is that otherwise they will block any attempt to do anything about climate change. Just considering oil there is around $100 trillion worth still to be pumped out of the ground in the next 30 years. All of this oil is owned by someone and all these someone's are not going to sit back and let their oil be made worthless (this is what would happen if we were to actually do something serious about climate change). Unless we pay off the fossil fuel owners they will continue to block any effective progress.

I disagree. There is no reason to think that just because oil owners stand to lose a lot of money, they will be able to block changes. After all, if they were able to effect arbitrary changes, they could simply force the government to give them another $100 trillion dollars.

The reason countries resist a carbon tax is not the value of oil per se, but the total economic impact, which is primarily from the reduced consumption of fossil fuels etc. (note all existing carbon taxes are on the burning of fossil fuels, not their extraction). The economic impact comes from people being forced to pay for more expensive alternatives. High oil prices don't actually benefit a nation, unless that oil is exported, in which case a national carbon tax won't effect it.

So the real barrier to carbon taxes is international cooperation. But the book argues that the easiest way to create international cooperation is with a global carbon tax (rather than global cap and trade).

Have the governments of Saudi Arabia, Venezuela etc. actually been blocking progress? If so, how? As far as I can see, the primary blockers of progress on carbon dioxide reduction have been:

1. Environmentalists, interfering with nuclear energy which is the only full substitute available now. (I'm optimistic about solar and wind, but there is much work to be done before they will be more than partial substitutes.)

2. Zoning laws, particularly in the US, encouraging people to drive far more than should be necessary.

3. The US government blocking (for what reason, I don't know) the introduction of a tax on aviation fuel that would cause the price of airline tickets to accurately reflect the real cost.

What are the other major ones? I'm letting the Chinese off the hook for the amount of coal they're burning because they have actually been making a lot of progress; I don't know of any gratuitous blockers there.

Yes the governments of OPEC along with the other owners of large oil deposits have been actively blocking progress. Where do think the whole climate change "skeptical" message comes from? The playbook being used is identical to what the tobacco companies used to block effective action on smoking for decades. As a society we would have been far better off buying the tabacco companies out and winding the industry up over time. If we had done this millions of people would still be alive.

Offtopic: It's funny that an article about polyglottism has a grammatical error in the title and a misspelling in the first sentence.

"Sceptical" is actually the British spelling of the word "skeptical."

Interesting. Thanks!

Why not? Unless I'm missing something, constructive interference is still additive and power loss is still inverse square.

Of course batteries also have power transmission inefficiencies. My intuition though is that wireless power has potential to be more efficient than batteries for two reasons:

- While building out the infrastructue is an enormous proposition, I'd guess that it is much more sustainable to maintain than batteries.

- When the application is propulsion, not having to carry a fuel source (e.g. battery) is huge. On a Tesla Model S, the battery is more than a third of the weight (450kg of 1235kg, according to Wikipedia).

How hard would it be to solve this deterministically?

Can someone comment on the game's physics? I am assuming:

  - constant horizontal velocity
  - gravity
  - flapping implemented via impulse
  - collisions are handled with bounding boxes

Maybe someone who knows something about optimal control (ODE) say whether this is analytically solvable? Of course there's still the practical stuff (numerical integration, I/O lag) to deal with but I'm optimistic.

If you play the game, it's actually quite trivial to program deterministically. :-) Flapping is not implemented as an impulse. It's more like jumping in Mario - it instantaneously fires a canned "flap" movement that is always the same.

Set flap_height = bottom of next pipe + constant.

If bird height < flap_height, flap.

Done!

It also looks like you'd want to avoid flapping into the top of the pipe.

Perhaps I should have said "threshold_height".

    threshold_height = bottom_of_pipe_height + 10 pixels; // or something

    if (current_height < threshold_height)
      flap
    else
      don't flap

If you never flap when above the threshold, you will not hit the top.

In another Flappy Bird thread (the MMO one), somebody posted this formula:

    Let distance between ground and top of screen=100. 
    Bird position after a flap at y=y0, time=t0:
    y(t) = y0 + 13.8 - 147 * (t - t0 - 0.288)^2

(https://news.ycombinator.com/item?id=7229018 -- note the original comment had "+ 0.288", but if you plot the graph this was obviously a mistake)

I tried it out in my own HTML5/JS Flappy clone (mine's not at all interesting or even done, but I felt I had to give it a try), and the movement seems really accurate.

I have no idea how they got to those numbers, however.

Interesting, I'd never thought about this before. In case you (or anyone else) are still wondering...

If an A3 sheet is X units by Y units (with X the long side) and A4 is 2Y units by X units then their ratios are X/Y and 2Y/X, respectively. If these are equal we have

2Y/X = X/Y

cross multiplying gives

2Y^2 = X^2

rearranging and taking a square root (X and Y are positive) gives

X/Y = sqrt(2).

Of course! ssh -X. Obviously requires conky (and a minimal X server) on the server.

no offense, I think that's effectively 'no'. :)

no one is running an X server on their production servers, perhaps unless somehow related to their actual purpose (screenshots, ui testing, etc.)

P.S. I agree this is pointless. The best solution in my opinion is simply ssh and [h]top or glances.

Eh, I was hoping to do it without running x on the remote server.

Great site design. A couple ideas off the top of my head:

- Let hikes to include GPS route(s) to display on the map.

- Link to the USGS topo map that covers a given hike: http://store.usgs.gov/b2c_usgs/usgs/maplocator/(xcm=r3standa...

- Add a bibliography to each hike.

- Scrape some websites to create "stubs" for new hikes and encourage users to develop these.

- Speaking of stubs, if you are going to have collaboratively edited content why not just build on MediaWiki or similar?

- Use OpenStreetMaps instead of GMaps and encourage users to add trails to OSM.

Great feedback.

-GPX support is top of my list of TODOs.

-I like the USGS topo / OSM idea. I'll have to do some investigation to see how it compares with Google Maps.

- I agree that a bibliography is a must. This is also something I would have gotten for free with MediaWiki. The reason I didn't build on top of that was, basically because I wanted to have complete control over the end result. Writing the code was the fun part for me. That being said, I wouldn't completely write it off.

- And I did write one scraper already for wta.org, but was unsure about whether that was ok to do or not...

Cool. Not a lawyer but I think that if you are not copying the main content (just the metadata) AND putting the source in your bibliography you should be okay.

Also one simple way to try to raise money for the site is to use affiliate links to Amazon for any [e]books in the bibliography.