What type of world or geography that makes aviation combat more important and superior than ground or naval combat

Question: So I wanted to write an Ace Combat type story but I'm having trouble what type of world that would explain the importance and mass production of aircraft. I tried to look at the map of Strangereal but I couldn't find any type of inspiration. The world I want to make is like an alternate modern world. It's also a multi-polar world which means that most nations and countries are equal in power, resources, and military strength. Most countries could own fighters jets and naval ships that they don't need to trade with others (just an idea but I thought that because of the ease of production of military vehicles that even mercenaries could grab themselves a fighter jet to join wars).
Comment: Why is this an issue? In our world, air combat has proven superior to ground and naval combat. So much so that even the navy employs planes. Why is Earth and its history not sufficient to answer your question? What's causing you to hesitate or care that the planet somehow influences this choice? Why is the fact that airplanes have the flexibility of traveling from anywhere to anywhere limited only by fuel not solve your problem?
Comment: People have, since the 1940s, regularly promoted the idea that air power makes naval and ground forces obsolete. These people have repeatedly been proven totally wrong.
Comment: You will have to elaborate what you mean by "important" to you?. Like JBH said. air power is the goto when projecting strength. But no matter how much you bomb a strip of land, you don't hold it until there are "boots on the ground"
Comment: @IseeDeadPeopleNot While I understand you want to have a more detailed answer, in order to accurately answer your needs it would be much easier if you provide details about your world's other constraints : Technology, magical lands allowed, etc. Otherwise we can only either make broad swipes at it or try our luck guessing some of them in your stead :).
Comment: @JBH actually most of our history shows that Airplanes are a great support tool, but in virtually no circumstance useful as primary means of attack. I know of only Desert Storm that did not end up a waste of resources using aircraft so much, and they had an absolutely overwhelming airpower advantage, first strike advantage and still needed the ground troops to also push up. Almost all other campaigns that relied primarily on air power failed in their goals and often were more a drain on the resources of the user than the opponent.
Comment: @Tortliena yeah sorry Im a bit new to using this website when asking questions.
Comment: @IseedeadpeopleNOT No worries, if next time it'll allow you to use less points for the bounty ^^.
Comment: @Demigan Except every naval engagement since WWI wherein an aircraft carrier was involved... It's curious how many people have concluded that the Q is asking whether or not airplanes could supplant the navy and army. That's not what it asked at all.
Comment: China is working in a supersonic anti-ship missile that promises to make ships virtually worthless in combat: https://asiatimes.com/2022/09/china-unveils-supersonic-missile-torpedo-anti-ship-weapon/
Comment: @CauêMoraes, which is great so long as they are also content to not to be able to use naval power either, say, to threaten Taiwan or to keep and maintain those artificial islands they've been building. Unless they assume that they'd somehow be immune to an equivalent system being pointed back at them.
Answer: Instead of making the terrain flat, make it extremely rugged and broken: very mountainous, sharp, cliffs, crevices. The Alps, The Rocky Mountains. Make all the available water large lakes, a few miles across at most, but frequent. Rivers can run, but are windy with steep 10-20 foot drops every 5 or 10 miles; often ending in waterfalls. These are not great for ships.
By doing that, you have disabled most land vehicles and ships. Marching armies move slowly. Only an aircraft can navigate rugged terrain quickly and easily.
We can find enough land we can clear for a township, or even a mile long airstrip. But aircraft, even gliders or Wright Brother era aircraft, are the superweapon in this terrain. Air battles would evolve naturally.
Below is a photo of Peru near Machu Picchu, the ancient mountainside village made of fitted stones. If your culture evolves here, gliders and machine powered flight would have enormous impacts, both militarily and culturally.
They learn to glide first, taking advantage of currents, gliding alone is 10 times faster than foot travel and saves huge amounts of energy. Climb one mountain, glide to the next, even if you lose 100' of altitude and have to climb again, that's better than climbing down a 1000' and back up 1000'.
People will develop fold-up lightweight gliders, and use them like we use bicycles. Heck in this terrain, they'd probably invent wheels, but may never invent bicycles; what's the point?
Eventually huge gliders will be devised for carrying heavy cargo.
Eventually the invention of engines to power the gliders will come along; regular aircraft and powered flight will evolve.
The knowledge of how to fly, over generations with migrations, diffuses into all cultures worldwide, until the primary mode of transportation anywhere is by air.
And thus the primary mode of warfare between nations is air battles.
Comment: Aviation would definitely be the best way to travel in such a world, but I think the biggest change this would cause would that war would just slow down all together. Mountains provide significant benefits to the defender (cover, ambush spots, etc), which aviation cannot completely negate.
Comment: I did wonder about this, but it occurred to me that there are a _lot_ of short lines of sight there, and it would be a bad place to fly a plane if there were some peeps down there with hand-portable SAMs. You'll also get some _really_ nasty weather conditions over terrain like that from time to time. Read up on [rotor winds](https://en.wikipedia.org/wiki/Lee_wave), for example (and various other kinds of [orographic effects on weather](https://en.wikipedia.org/wiki/Orographic_lift)).
Comment: @StarfishPrime Fly higher. I fail to see how this is any worse than a military helicopter, and we still use those despite ground artillery. And, of course, there are evasions; A good helicopter pilot can use the hills and mountains for cover, to hide, and for surprise attacks.
Comment: @Tortliena You develop quick take off and landing facilities. Aircraft can take off and land on an aircraft carrier with a runway about 300 feet long. The Wright Brothers first "runway" was 60 feet long. If you develop your flight capabilities from gliders, the runway is: jump off a cliff, catch updrafts, and land on your feet. Basically their aircraft will be invented and evolve with their landscape in mind. We could make long stretches of flat runway, so that did not constrain our aircraft development.Their aircraft development would always retain the quick take-off and landing ability.
Comment: @Tortliena Sure. Or, in a mountain, a short runway off a cliff, counting on the fall to generate lift. Or, like the aircraft carrier, the jet slows as much as possible, and has a hook to catch a cable and that stops it quick; if a pilot misses the cable they hit the gas, take flight and circles around to try again.
Comment: @OsiriumWrites You are attempting to answer the question in comments. You should just scroll to the bottom of the page, and put these comments in an answer. And delete them from the comments here. These comments are for questions or clarifications about **my** answer, not a place to write your own answer.
Comment: With such accidented landscape, how do you put landing areas ^^? A focus on air warfare means you need much more places to land and take off than what currently exists.
Comment: @Amadeus Adapting like making heavier use of helicopters and VTOL planes. I see :)
Comment: @jb6330 True. But aviation can deliver troops to the top of a mountain, and high ground is still an advantage in battle. And the question is about "aviation combat" being more important and superior to ground or naval; I think an aviation dominated society, perhaps with few or no motorized ground vehicles, would certainly do most of their fighting from the air. Reconnaissance, bombing, strafing, etc, including aircraft defending against enemy aircraft.
Comment: @StarfishPrime The MANPAD threat is countered by using the terrain to deny the missileer time to track you and launch their missile.  The very rugged terrain gives plenty of terrain to hide behind if you have an autopilot that can fly you around the terrain without flying you into it.  Bombing your target without being killed by your own bombs becomes problematic, though.
Comment: @Amadeus, should it happen again, please flag for moderator attention.
Answer: Large flat treeless islands or continents in large quantity, I'd say. Vast grasslands and shrublands (eg. prarie, steppe, veldt, pampas), nice for farming. Giant flat deserts, like quite a lot of Australia. Easy to put in an airstrip wherever.
First for the wet navy:

Aircraft have been bad news for surface wet navies since Pearl Harbor, and antiship missiles have only made this worse.
Carriers are only needed when there's no handy airbase.
If there's more land and less Pacific, there can always be a handy airbase.
Shore-launched antiship missiles are increasingly dangerous when there's more shore and less open ocean.

And for the dry army:

Long lines of sight with little cover are bad news for everyone on the ground. With no mountains and no trees, everyone on the ground is badly exposed, and no-one is going to dig trenches across a thousand miles of plain or desert.
Modern antitank missiles are pretty bad news for tanks already.
Specialist ground attack aircraft are extremely effective in the right sort of terrain.

The only thing you hand to handwave away is antiaircraft missiles, and that's a bit more of a challenge. Any countermeasures to SAMs also work against regular AAMs, and potentially against air-to-surface weaponry too. This needn't be a bad thing if what you want is WWII-style gun dogfights and A10s with ridiculous cannons.

Remember this doesn't have to be the whole world (which might be a bit too unrealistic), but just enough of it to provide an interesting setting. Maybe tanks and soldiers and carriers are the best things everywhere else in the world, but no-one cares because your flyover continent has all the resources that everyone else wants and needs, and so that's where all the plotworthy fighting happens.
Comment: You could argue that large extremely open terrain is ideal for land armies (islands too)... as defender. You WANT open sightlines that enemies have to cross, its why defenders tend to remove all cover near their defenses and why attacking an island across the coverless beaches is so difficult. And trenches are perfect in open terrain to provide protection even from airstrikes, just make sure you have various lines. Having flat terrain is ideal for aircraft to detect their opponent though, just not very good at trenches usually (or rather, trenches that you know are filled)
Answer: To make aerial combat more prominent, here are my choices ranked by incentive to develop air warfare. Most are inter-compatible between each-other :
1) Sky islands
Laputa, Dragon hunters, Sunless skies, trapped in a Dating Sim: The World of Otome Games Is Tough for Mobs (this title is so long o_x)... It's simply a set of islands or other objects floating in the sky. Alternatively it can be floating asteroids, but reacting for people like they're on Earth. This is your best choice over anything else. Having a sky world is a very high-incentive to make air-warfare, as any other warfare isn't just viable at all. This is shown in all 4 references I gave
Why?

There can't be any naval warfare at all, because... Well, there's no sea x).
Bridges between islands is expensive. And they get destroyed very easily. Land warfare is therefore very unreliable beyond the islands they're set on. Land troops will need air transport to conquer territory.
You don't want to fight enemies on your land, especially with key infrastructures, that's the last resort defense. Because there are always empty spaces where no flak land cannons can reach, you can't have a buffer zone to prevent this. Therefore you have to send fighter planes to intercept invasions instead.
Any commercial caravan will be in the air, therefore almost every pirate or corsair attacks will be in the air, too.
People necessarily have to invent efficient planes, helicopters and blimps to travel between islands, and therefore would have focused their research on it.

Why not?

For a sky island world to exist you generally have to admit there is some magic or physical singularity involved.

2) Lava/acid oceans worlds
This is a slightly less magic-prone alternative to sky islands. Take a world, replace the seas with either lava, acid, or something else which prevents boats from floating. Or its crew from living.
Why ?

There's little to no naval warfare at all. It's one less concurrent to care about.
Like with sky islands, land warfare is contained within the land it is lying on. To provide land troops from another continent/island, you have to use air.
Infantry are removed from the game or would require very heavy support from tanks and planes to get protected from rains (acid or pyroclastic clouds).
If people do manage to bypass some of the lava/acid damage, they get access to a new cheap and effective against any unprotected or damaged land troops/structure, yet working at its most potential from altitude : lava/acid bombers. Bonus for lava since it solidify against any resilient structure left.

Why not?

Living conditions are likely to be extremely hard there. Technology or/and magic requirements to just survive there is likely to be high.
Meteorological conditions are likely to be harsh, too. You can't rely very much on visual identification and do need the instruments and specialized technology to navigate an aircraft in it.

3) Lower gravity, 3b) higher air density
This is the main element which prevents air from being used to its full potential. Make your planet less heavy, or increase its air density to make the cost of rising things up in the air much lower.
Why ?

Drastically improves air vehicles max carry weight, which means increased armor, weaponry, troop transport or autonomy (fuel). You can have actual air tanks with more stable air frontline now.
Maneuvering with planes is easier : You can have a lower speed and you'll have an easier time dealing with stalling. Your tactical playground is also bigger (you can reach higher-places).
Take-off areas will be much shorter due to higher-lift/lower gravity : You can have more airfields with more planes taking-off with less cost.
It's much less expensive (economically and technologically) to produce aircrafts. You can have "cannon fodder" aircrafts and replacing/repairing any aircraft will be easier, much more than other troops would gain from these world changes.

Why not ?

Higher air density can decrease airship top speeds, one of its main strength.
Lower gravity means ground and naval forces can carry more weight, too. However, they'll never get the same speed as air, and the profits of much higher weight capacity suffer from diminishing returns.
Tanks will get more armor... But at the same time they will have to use it to protect against aircraft which'll hold heavier weaponry and be more numerous.
This doesn't make airships a true necessity, rather a much stronger card to play.

4) Archipelagos or plain oceans
If you can't remove naval warfare, think the opposite, remove land warfare instead. The principles are about the same as sky islands, just you have moving boats around now.
Why ?

Planes work very well with ships because they cover each-other weaknesses : autonomy and raw fire power for air, speed and coverage for sea.
Planes excel at destroying key objectives. Islands and any other targets like offshore platforms are very easy to determine as "key objectives".
Because there are always empty spaces where no flak land cannons can reach, it's much harder to have a buffer-zone to prevent air invasions. You could use ships to make up for that, but they can be outmaneuvered (slow...) and are already split protecting against 2 other battle planes (sea surface and underwater), so...
You need only one plane with one well-placed torpedo to sink a whole ship and its crew. You need several bombers to kill all infantry and tanks in an area.
Difficult to land shorelines could make sea transport much trickier to do. Land assaults are likely to need the support of air.

Why not?

You're very dependent on naval warfare, especially regarding aircraft carriers. At the very most you're split between 50% air / 50% sea warfare, if not less.
You don't have much ground to land and take-off. This severely limits the total number of planes available at one time.
This doesn't make airships a true necessity, rather a stronger card to play.
Comment: For rocky planets, bigger definitely means more gravity, with only a small adjustment for density. On the other hand, higher gravity isn't correlated with a thicker atmosphere. You can pile a lot of atmosphere onto an earth-sized planet. Venus, for instance, has an atmosphere 95x that of Earth, while being only 81% as massive.
Comment: I like the idea of 3 and a bit for 4. But I wonder if gravity decreases depending on the size of the planet. If for example the world is like the size or half of a super earth (10 times the sizes of our earth), would gravity be a problem there?
Comment: @IseedeadpeopleNOT That's not the main point of your question (it's worth its own question), but... According to [Newton laws](https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation), surface gravity is both a factor of distance and weight. Increasing size helps "squarely" as much as reducing weight, but at the same time you add a lot more weight (no exact number, but I guess it's more cubic). This is why bigger planets tend to have higher gravity, like displayed on this [list of planets ordered by size](https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size) :).
Answer: You got two examples from existing works.
A world with floating islands like the Japanese game Grand Blue Fantasy. Since you definitely need to fly to get to another human settlement, most of the transport in that world is going to be aircraft or airships.
Or, just like the anime The Magnificent Kotobuki, where there is very little ocean--which makes transporting goods by land possible, but very time-consuming. The existence of aircraft and airships makes transportation time shorter.
Answer: In other answers, scenarios are suggested where enemy is difficult to reach by land or sea therefore you attack by air force. Well! you bomb the enemy land or dog fight with the enemy air force, then what?
Navy, army, air force, all have different uses.
Navy is used when

enemy can be reached by sea.
enemy is also fighting with navy and you want to destroy it.
enemy's strategic places are close to the coast and can be attacked
by ships.

Army is used when

enemy can be reached easily by land.

you want to capture and control the enemy's land.

Air force is used when

enemy's strategic places are away from the coast.

enemy cannot be reached easily by land because of large distance,
mountain, sea, thick forests, marshy land, rivers etc.

you only want to destroy enemy's places but you don't want to capture
or control enemy's land initially until the enemy becomes very weak
and unable to fight when army reaches.

REMEMBER

Many people think that army and navy are becoming obsolete. But you
cannot capture and control the land without army (unless you throw
enough nuclear weapons so that there are no people left and the land
becomes useless). You need navy to save your coastal cities, sea trade routs and
ports.
If your borders are common with or close to the enemy, you will need
army at some stage. Only air force may not be enough.
If the enemy's land is flat or desert, air force and later on army is
effective e.g. Iraq.
If the enemy's land is full of mountain, sea, thick forests, marshy
land, rivers etc., then air force can destroy enemy's places and kill
many people but capturing and controlling the land is very difficult
e.g. Vietnam, Afghanistan.
Comment: So there isn't any kind of situation where aviation military would be prioritized than ground forces.
Comment: Every force has its own uses and purposes but occupation is done only by the army. On or about April 26, 711, the army of Ṭāriq Bin Ziyad, debarked at the foothills of Gibraltar (Jabal Tariq), burned the ships and Ṭāriq said to his companions: "fight or die".
Answer: The Problem
You want air force to be the main solution to warfare in your world, and want a realistic, believable reason for it to be that solution. You want army and navy to exist, but be severely overshadowed by the aviation forces of the major factions in your world.
The Desires
The Navy
These forces generally want

Easy access to vital targets via waterways.
Clear line of sight on enemy vessels.
Waters relatively free of aquatic enemies (more important the earlier in history you go) (Giant squids, Krakens, etc.)
Large areas of water to traverse to get to a location
Natural propellant (Wind, Tides, etc.) for early ships

The Army
These forces generally want

Easily forage-able land, and should that not be the case
Easily defend-able supply lines.
Flat expanses of ground that can be covered easily
Clear line of sight on enemy forces (flat ground good)
Cover from line of sight of enemy forces (flat ground bad) (funny how that works)
Safety from hit-and-run tactics (boats, air, etc) (away from coasts, under trees)
Land route to target

The Aviation Force
These forces generally want

Easily traverse-able airways (low turbulence, few obstacles)
Cover from anti-air technology (could be as simple as clouds, depending on tech level)
Clear targets
Large distance / difficult terrain to cover

Taking What They Hold Dear
The Navy

Perhaps your world was once an ocean world, but some event led to the sea level on your world suddenly dropping by a large margin.

If your oceans dropped by ~1,000 meters, you'd be looking at 800 meter tall cliffs on most continents, and that is terribly sub-optimal for navy forces.
Foggy waters. If your world's oceans and rivers are constantly shrouded in fog, navy would become great for small stealth operations, but would rarely be used for large-scale war operations. This, of course, inhibits your ability to have aircraft carriers, as well, as it's much harder to land on things you can't see, but it allows for secret refueling stations left out in the sea, perhaps broadcasting on a certain frequency to alert allied planes to its presence.
Squids, Krakens, and Monsters Galore! The simple addition of terrors of the deep are certain to keep early tech levels off the seas, or at the very least extremely cautious and afraid for their journeys through the waters.
Oops! No water! No water? No Navy. Simple as that. Although this option is bland in my opinion, it is a possible option.
The gods hate us. The natural forces that be are always forcing ships back in towards land. This is hard to pull off in a way that feels natural, but something you could keep in mind is that early ships relied on wind to go far. If the wind was constantly pushing you into land, you'd have to wait until a new invention (engines) was made in order to go anywhere close to as far with ships. Or row.

The Army

Deserts. They suck to attack, unless you're already used to them. Unrelentingly hot, deserts require you to drink way more water, and are flat open ground that is great for defenders to see you in. Supply lines are made difficult by soft sand, and weapons and vehicles can easily be gunked up by that same sand.
Mountains. They're hard to traverse for ground units. Unless you travel the peaks of mountains, someone can always attack you from above, and travelling at the peaks takes more time and energy. Even a mountain range between territories is a huge deterrent to land forces.
Oceans. Most people can't walk on them. Put them between territories, and voila! A huge deterrence against land invasion is born.

Strengthen Your Air Power

It's okay to have paratroops.
Armies are vital in taking and holding cities, and large planes with great defense and fuel capacity to support carrying many troops is a necessity if your world is mainly based around planes.
Bombers.
This step is usually done before sending in the ground forces, but after defeating any fighter aircraft in the area. These guys are slow and powerful. They have high fuel capacity and an even higher weight capacity. They drop bombs on your target location, 'softening' the target, so that when your troops arrive, they meet minimal resistance. If everyone lives underground on your world, these planes become near-useless, as causing damage to empty ground doesn't do much to the enemy.
Fighters.
These planes will be small, light, and fast with air-to-air combat in mind. These will be your fastest planes, and your planes most likely to go down. With that in mind, the pilots flying these planes will be the most skilled, and they will have the best protections in place for escaping the plane alive should the plane lose function. They do, however, have low fuel capacity, so they won't be going very far without help. These kinds of planes love cover. Especially once you start getting into laser-guided and heat-seeking missiles, having a mountain to dodge behind can mean life or death for the pilots of these guys.
Mid-flight Refueling.
The smaller and faster the plane, the lower the fuel capacity. If you have small fighter planes, they will need somewhere to refuel. This could be on the ground for defenders, or on aircraft carriers or mid-air refueling for attackers. If you choose to go the mid-flight refueling route, you'll need aircraft specialized for the task, and they'll need to stay away from the air-to-air fighting.
Carriers.
If it's possible to land on them, carriers are essential to attacking overseas. Even the most gassy of planes can be on fumes after crossing the Pacific. It's unwise to attack a target from the air if you lack the ability to stay there. So you'll want some way to get your planes across the expanse or refuel them once there, and a carrier fills both of these roles. If your planet has oceans, these are a great idea.
Reconnaissance.
These will be your most stealthy planes. The ones with cutting-edge tech to keep them quiet and unseen. These will go out long before your attack commences to set up likely targets, and mark down enemy defenses. If your planet doesn't have clouds of some kind, these planes will be virtually non-existent in earlier tech levels, and very difficult to pull off in later ones.
Comment: As far as I am aware in modern air power its the fighters that are fastest. A bomber's best defense is getting in and out while trying to outrun any response. Fighters instead rely on their maneuverability, detection ability, stealth/electronic warfare ability and the amount/capability of their missiles. modern fighters are often slower than their predecessors as a result.
Comment: @Demigan I'll look further into it. However, you seem to contradict yourself in your critique?
Comment: sorry meant "bombers are the fastest", didnt get much sleep last week.
Comment: @Demigan After looking into it, I found that the fastest military planes still in service (apart from the boeing X-37, though that hardly counts) are all fighter jets. Not to discount your assertion, as bombers are certainly much faster than they once were.
Answer: Storm Hawks

Storm Hawks is a cartoon about crystals and dogfights and maybe friendship and believing in yourself too. The real Storm was the one inside us the whole time.
They have their world set up to explain why there is so much zipping around in little airplanes and also lazer-swordfights to keep things PG.

Storm Hawks is set on a fictional world called Atmos, a largely mountainous world consisting of scattered, towering, plateau-like land masses known as terras.

Directly below the terras lie the Wastelands, the most dangerous area of Atmos, with infernal fires and wicked creatures. Because of the geography, travel is mostly dependent on flight.
Comment: Is it possible to remove the poster and put a link to a wikipedia page or equivalent instead? Knowing there's a red-haired guy and a crazy-looking rabbit in this show doesn't detail much about your answer's core point :p.
Comment: @Tortliena Fair point. There is now a link AND an airplane.
Answer: What about a world with almost no land and the ocean is a very dangerous place.
Maybe the depths are inhabited by terrible and indestructible leviathans or a savage race of deep ones that love the taste of human flesh, creatures so vicious that humans have to build floating cities sustained by zeppelins in order to survive.
Maybe the atmosphere is so dense that any child can be a aeronautical engineer (because flying will be pretty easy) and some crazy airplane designs are completely possible.
Well, if more ideias come to mind, I will be back here editing it.
EDIT: apparently, denser atmospheres make the air in lower regions toxic for some reason, so I think it makes any terrain dangerous enough.
Comment: Sounds like a good idea but the world I'm trying to make is a modern AU idk how civilization can grow if there's little no land
Answer: An increased importance of aircraft could become likely on a world with limited metal deposits. Naval vessels are among the heaviest vehicles on the planet. The lightest tanks are as heavy as a fighter jet. If there was a limited supply of iron, aluminum, titanium, and other metals, their use for war machines would likely be restricted to those which give the biggest bang for their buck. As fighter/bomber planes can sink a naval ship, there is the risk of losing a significant metal investment should planes attack a naval ship.
Tanks are also at risk of destruction from aircraft. The term "tank plinking" came into being during the Gulf War for pilots using precision munitions to destroy enemy tanks and armored personnel carriers. The best way to increase the survivability of a tank is to add more armor. That is not really an option on a planet with limited metal reserves. They should be able to make 4-5 jets for the metal cost of a single large tank. It makes more sense to make hundreds of planes at the same cost of a few dozen tanks.
Other side effects of such a world would be the use of extensive public transportation in leu of private transportation. Vehicle metal would be limited to the engines and supporting components, while the frames would be fiberglass and other lighter non-metallic materials. Cities would be built close together to prevent urban sprawl and decrease infrastructure costs. It costs significantly less metal to build an apartment building which can house 100 people than to build houses capable of housing that same number. There would be greater reliance on plastics, wood, and other alternatives. Even things like sign posts would be made from wood instead of steel.
Alternatively, you could have an advancement of automation (3d-printing) which enables the rapid production of things such as aircraft, but struggles with heavier vehicles such as tanks. If your nations can produce 100 fighter planes in the time it takes to make a single tank, there would be little reason not to use planes over tanks. Just say that your automation cannot produce metals over a certain thickness, as planes use thin sheet metal it is not an issue. Over time, this use of aircraft could become a cultural preference.
Of course, this type of efficient production would have a ripple effect throughout your world. Production of most goods would become easy enough to reduce the bottleneck of supply and demand. Perhaps this is how your nations gained equal status. Once a nation adopts the widespread use of this automation, they quickly attain status on par with the rest of the nations. As a nation starts to expect rapid production of goods, the idea of waiting significantly longer for something like a tank becomes less workable. If replacement times are measured in months as opposed to days, it becomes harder to argue for that option.
Alternatively, you could have an Einstein type character who designs a "perfect" aircraft and releases it to the world in the hope of preventing wars (or whatever other motivation fits your narrative). This is what the Expanse novels did for their Epstein drive. The use of these super aircraft turns the tide of battle so drastically that all nations prioritize their use. This does not have to be a specific aircraft, but could be an AI control system or something else which makes planes significantly better on a battlefield. As the battlefield losses against these aircraft increase, the only option is to copy that design. Continuing to field tanks which are nearly instantly destroyed would cause public backlash. This happened during the Iraq/Afghanistan wars when unarmored Humvees and other vehicles were easily destroyed by the local forces. It resulted in several completely new lines of vehicles to combat the threat. Eventually, your nations would adopt the new aircraft out of necessity. A super airplane would have the least impact on the other aspects of your world.
Answer: You want to give as much advantage to aircraft and as little to the ground/navy forces. That means:

large flat terrain with little to hide in for easy spotting and detecting.
large pieces of cover that hide aircraft approaches and make it easy to pinpoint potential radar sites and reach them. This means that many singular mountains or hills are present with only a few kilometers of flat terrain distance.
no easy supply routes for ground armies. That means many bridges or roads that can only be constructed in specific area's making it easy to cut off. Swamp lands for example.
little deep enough water with enough connections to other bodies of water. If the navy is stuck at say Vietnam types of water area's then the navy can only use small boats.

This would mean that the best methods of attack would be scouts that radio in enemy ground/navy forces or supply lines which then see strikes from helicopters and aircraft that use the few large (and devoid of meaningful vegetation) pieces if cover to approach their target. The defender's best option is to use MANPAD's for the lowest flying units and station vehicular missile systems behind or on the sides of the mountains and hills. The second most used unit would be artillery due to its range, but its also a very supply hungry unit*. Aircraft are hungry too but land far behind their own lines where supply lines are easier to maintain.
Something else to consider: airships. While some highly public crashes made airships look like they were slow and made of explodium, the truth is that they are the toughest aircraft to have ever existed. In fact jet engine aircraft were in the same spot at some point where people thought they were more expensive, more fuel consuming and more dangerous alternatives to prop aircraft that just kept randomly crashing despite being young planes. They found out that it was the lack of rounded edges on windows that caused the planes to crash due to stress failures.
Airships, properly build and with the same decades of design as modern aircraft behind it, would be a magnitude tougher than the toughest modern military aircraft. Multiple lifting gas bladders, not using highly flammable materials for the outer skin, superior construction materials, modern weather and electronics for safety and detection of leaks, heavier-than-air airship designs and higher redundancy than planes would all help make these excellent additions to modern air power.
A simple example: airships would be far superior to modern early warning aircraft like ELINT or AWACS due to the larger and more powerful versions an airship could install and the ability to be on-station for LITERAL DAYS compared to several hours (and even in WWII airships could fly across the atlantic and back in one go without in-air refueling). Additionally the ability to use offset armor plates to detonate incoming missiles prematurely and catch shrapnel with spaced armor designs would help protect vital area's (on top of again redundancies). Having another airship as a missile barge would also supplement your airpower ability, as missiles fired from it dont have to climb as high to intercept their targets, meaning more fuel for speed and chasing for a larger effective range.
*I think Russia's current supply lines are for 50% dedicated at feeding their artillery in some way (ammunition, fuel, food, maintenance along with the consequences of all the maintenance and fuel required to maintain a supply line to the constantly moving artillery pieces).
Answer: Increase air pressure
If the air would be more dense, nature would grow stuff that floats, and with stronger winds there would be stronger skin and stuff (to a degree) that would allow even early craftsmen to attempt floating, or making deltaplanes or similar contraptions to quickly cover ground while descending. The atmosphere contents as well as biology could be slightly altered to avoid broken physics or biochemistry, say humans could develop protection from decompression issues raising from them travelling heights, without actually changing appearance of lifeforms, except those that specifically take advantage of dense air and are impossible on Earth. The very same alteration could as well harden sea travel, because sail-based ships might not cope with more harsh weather in deep sea, and with advent of fossil fuels and combustion, using hot air to lift up zeppelins might even be energetically cheaper than making a sturdy ship capable of sustaining high winds and propel it with diesel.
Use Pangaea
Employ a scenario where the sea is too far for involved parties to ever take part in the story, except maybe as a place to refuge or seek death. Everything else should be either land or air, and air travel is by definition faster than land.
Answer: Post Apocalyptic wastes:
Your terrain was once verdant farmland, forests and lush countryside. No more. Once great natIons are now limited to bunkers, isolated valleys and islands. Vast regions are filled with radiation, deserts, mutants, and lingering super anthrax.
The seas are poison are filled with mutant monsters. Drone AI nuclear submarines operate autonomously attacking ships like a cross between Moby Dick and the Nautilus, still fighting a long-lost war.
Many nations prepared for the apocalypse, building up aviation industries around aIr bases. Their best and brightest were saved to rebuild civilization. Advanced automated factories churn out advanced equipment as fast as resources can be found. But  the remaining bases are isolated and far apart. They scavenge the wastes with blimps and dirigibles, retrieving supplies and equipment to rebuild.
The new distribution of resources and power looks quite different  than it did. Battered superpowers scrabble to hold on to vast territorial claims. New powers that came through the war less damaged refuse to  recognize outdated maps.
The table is set for a world where air power rules, fighting at vast distances in a world where armies dare not travel and every port has been destroyed.
Answer: Who cares about ships... Just build a plane!
Alternative option here: Earth like planet with different gasses and main element compunds. In this world, lets say there are easy to make mixtures creating "lighter than air" liquids and/or gasses.
Add some certain metals with less weight, extreme flexibility and they are easy to manufacture.
Aerial combat is effective in our world as it is.
One of the problems with air attacks is, well, building a good plane or airship is hard. Engineering when it comes to planes, needs to be deadly precise. And even then there are accidents. But what if... There are easily accessable good materials to build planes cheaper, more efficient. If hindenburg accident didn't happen, or if people had access to large amounts of safe light gasses for airships, they wouldn't be so rare as they are now.
If building and maintaining a plane or air ships would be this easy, I wouldn't spend most of the budget on land or sea based weaponary. Mostly aircraft carriers, land based portable aircraft launchers for faster take-off, and enough fuels. This way, most of the combat would continue on air, and other units would mostly support air units. Because, why spend money on building a good ship when you can build 30 nice planes. With half the price and material.
War is a battle of information, resources, morale and economics. If one method offers significant advantage on even one of these, then people would naturally choose that more frequently.


Taking apart wood bed frame with no screws

Question: This bedframe seems to have a slot joint system but I can't seem to understand how to take it apart. There are two pegs I think will allow me to slide the side out but I'm not sure how to get the pegs out.
Comment: ...also...  were you the person who cut the slots into the pegs? Telling us these things without making us guess is helpful in getting to an answer that works faster...
Comment: I removed the staples holding the pegs in. I tried lifting before I posted but after everyone here suggested just lifting, I tried the other side and it worked! It looks like the side I was working on it stuck so I'll have to try to take a mallet to it or something.
Comment: Have you tried just lifting? Or depending how much it's been painted, hitting in a direction opposed to gravity? The extended slot below indicates a likely "no need to remove bolts" disassembly by lifting the rail and then moving the head/foot away from the rail.
Comment: Looks to me that staples were being used to hold in those metal (?) plugs when the bed was painted and then the staples were removed at some point.
Answer: That looks like the board just slides upward.  See the slot underneath the board?  Lift up on the board with the pegs, and gently tap the board with the slot downward using a hammer or something.  The board with the pegs probably has some J hooks that slide into the slot and hook over a peg, dowel, or whatever that crosses through the slot.
Edit:  Here's a picture likely resembling what you have that goes into that slot.
Comment: I just noticed... see the round circles in the post?  Those are the pegs that the J hooks "lock" onto after being inserted into the slots and then lowered down.
Comment: I couldn't remove the pegs, but I tried the other side and it did lift up!! SO the side I was working on was stuck. I guess I'll have to take a mallet to it.
Answer: My expensive wooden bed frame has what looks like the same things. If so, they are plugs that have to be removed to access the screws behind those plugs holding the bed together. Just take a very small screw driver and try to remove those plugs.


Fatal error: Class 'Altima_Lookbook_Helper_Data' not found in /home/offerbea/public_html/app/Mage.php on line 547

Question: I have installed it from magento connect,  and now in my back-end it displayed as it.
Please somebody help me how to fix it.
I gues it causing by i was put the compliation mode in on.
Thank you
Comment: put the compilation mode 'off'. Then refresh the cache and logout and login back. Still the error is there, check whether the installed module contains a helper class as Data.php. If exists check the class name is correct.
Answer: Please Check in your Module like
If your module in Local folder then
app/code/local/Altima/Lookbook/Helper/Data.php file Available or not if not then please create the file as below code.
<code><?php
  class Altima_Lookbook_Helper_Data extends Mage_Core_Helper_Abstract
  {
  }
</code>
Now refresh your cache and test it


How to create a file even root user can't delete it

Question: How to create a file even root user can't delete it ?
Comment: While tante's answer should cover your question, one meta-comment to it: It would be much easier to answer if you added your rationale to your question. Maybe there is a work around to your problem not consisting of preventing deletion of the file(s)?
Answer: Simple answer: You can't, root can do everything.
You can set the "i" attribute with chattr (at least if you are on ext{2,3,4}) which makes a file unchangeable but root can just unset the attribute and delete the file anyways.
More complex (and ugly hackish workaround):
Put the directory you want unchangeable for root on remote server and mount it via NFS or SMB. If the server does not offer write permissions that locks out the local root account. Of course the local root account could just copy the files over locally, unmount the remote stuff, put the copy in place and change that.
You cannot lock out root from deleting your files. If you cannot trust your root to keep files intact, you are having a social problem, not a technical one.
Comment: someday you too will be an interviewer and be able to ask nonsensical questions of your own: "can root create a file so large that he can't `mv` it?" (which is a lame joke based on Christian theosophy, and a terrible joke if you you aren't familiar with field)
Comment: @msw: One could argue that it's a terrible joke even if you are familiar with the field.
Comment: This question is asked by an interviewer to me. I don't know the answer. I asked to him for answer. He said it possible and find solution by yourself.
Comment: @matthew crumley: guilty as charged :)
Comment: @msw: I just noticed that you even admitted it was a lame joke. And FWIW, I like (some) lame jokes so I actually liked it. This is getting pretty far off topic though :)
Answer: Put it on a CD-rom! ;)
(this should be a comment but I can't do comments...)
Comment: This and the answer by @mouviciel is the only correct solution. Even the almighty @root is still bound by the rules set by the hardware.
Comment: There is a sense behind the reputation limit for comments ;-) Just a small thought-provoking impulse. no flame intended ;-)
Comment: Well, you can now comment because you posted what you thought should be a comment, as an answer! So this actually helped you XD.
Answer: Put your file on a readonly filesystem. This may be a remote FS where root is no longer root, a CD-ROM or a removable device that can be write-protected, e.g., a SD card.
Answer: Long ago I wrote a kernel patch (to 2.2.ancient) where attempting to delete a file called SELFDESTRUCT killed the calling process. This guarded against accidental "rm -rf *".
Comment: long ago and far away.  How did you actually do it (commands) ?
Comment: Wow, I like that idea!
Answer: You can use chattr +i to make a file immutable.
Of course a savvy user with root access could still use chattr -i to remove the immutable attribute and then delete the file, but they could undo any of the other attempts to block access listed here as well.
I would argue that chattr is the correct Unix way to do this.


Deriving calculation formulas for torsion and curvature

Question: With much blood, sweat, and tears, I have managed to derive the formulas
$$k = \frac{||a' \times a''||}{||a'||^3}, \quad \tau = \frac{\langle a' \times a'', a''' \rangle}{||a' \times a''||^2}$$
for the curvature and torsion of a smooth regular space curve $a$. In general, is there any elegant way of proving such formulas, or is it inevitably a mindless differentiation bash and application of cross product identities? I suppose these are what you'd call calculation formulas, so there might not be any meaning to assign to the right-hand sides, and hence my hope might be in vain. Nonetheless, thanks for any advice. Even any suggestions on how to cull the working would be good -- I spent at least two pages on the former and around three on the latter.
Comment: The numerator of $\tau$ is a [scalar triple product](https://en.wikipedia.org/wiki/Triple_product#Scalar_triple_product). There are a number of identities about them. Other possibly useful facts include $\Vert v \Vert^2 = v \cdot v$ and $\Vert v \times w \Vert^2 = \Vert v \Vert^2 \Vert w \Vert^2 - (v \cdot w)^2$. There are also identities about cross products of cross products. Finally, remember that differentiation obeys the product rule for both dot products and cross products. At the very least, all of this should mean that you can avoid working in coordinates.
Comment: Could you add your detailed demonstration? I've looking through internet and I cant find something useful...
Answer: It shouldn't be "a mindless differentiation bash" if you write down the equation
$\alpha' = \upsilon T$, where $\upsilon=\|\alpha'\|$, use the Frenet equations and chain rule to differentiate twice. It helps to economize a bit by remembering that $w\times w=0$ for any vector $w$. In particular, $\alpha'\times\alpha''$ will point in the $T\times N= B$ direction, so you'll need only the $B$ component of $\alpha'''$. (P.S.@Jesse Madnick, I don't think the identity for  $\|v\times w\|$ is needed at all.)
Answer: Wolfram mathworld - http://mathworld.wolfram.com/Curvature.html
gives an easy proof of the first formula. The second one can be derived in a very similar way. The main idea is to write the derivatives of the curve in terms of the basis given by T, N and B. This should simplify the computations considerably.
Answer: The way I simplified the computations for myself at some point was by writing $\frac{d^2a}{ds^2}=\frac{d^2a}{dt^2}\left(\frac{dt}{ds}\right)^2+\frac{da}{dt}\frac{d^2t}{ds^2}$, figuring out the derivatives with respect to $s$ on the right hand side, and using the formula for orthogonal projection of $a''$ onto $a'.$ You can rewrite the curvature you wrote above similarly, using $\frac{dt}{ds}$, and writing it as the magnitude of the same projection.
(Note that $\|$orth$_{a'}(a'')\|=\frac{\|a'\times a''\|}{\|a'\|}.$)


How to change default view of library using javascript or programatically?

Question: I have a requirement where I have to change view based on users logged into the portal. If user belongs to guest view then view should be different and if he is logged in as admin a different view should be displayed. I want to do that by changing the default view to the view I have created. How can I do that?
Answer: This code change the view by taking the id of the new view by list. (you can use your own logic to change it)
<code><script type="text/javascript">
//declare a variable for the exisitng view
var existingview;

function loadViewAndChangeIfExists()
{
  //get the current client context
  clientContext = new SP.ClientContext.get_current();
  //if the client context exists - proceed
  if (clientContext != undefined && clientContext != null) {
    //get the current web
    var web = clientContext.get_web();
    //get all lists
    var listCollection = web.get_lists();
    //get te current list by name - alternative use getById(guid)
    var list = listCollection.getByTitle("COM");
    //get all current views of the list
    var viewcollection = list.get_views();
    //get the view that you will change
    this.existingview = viewcollection.getByTitle("MYVIEW");
    //load your existing view and execute async
    clientContext.load(existingview);
    //the asynchronous execution will try to load the existing view
    //if the view does not exist - it will call onQueryFailed - else it will call changeView
    clientContext.executeQueryAsync(Function.createDelegate(this, this.changeView), Function.createDelegate(this, this.onQueryFailed));
  }
}

function changeView() {
  //the varible existingview is now loaded with your view
  //get the current CAML query
  var existingquery = existingview.get_viewQuery();
  //do somnething with the exisitng query here
  //...
  //reset the query (as sample)
  existingquery = "<Where><In><FieldRef Name="ID" /><Values>";
  //add a CAML filter with the current selected items
  var selectedItems = SP.ListOperation.Selection.getSelectedItems();
  var i;
  for (i in selectedItems) {
    existingquery += "<Value Type="Counter">" + selectedItems[i].id + "</Value>"; //add
  }
  //close the CAML XML
  existingquery += "</Values></In></Where>";
  //assocciate the existing view with the changed query
  existingview.set_viewQuery(existingquery);
  //update the view!!!
  existingview.update();
  //execute the statements async - onQuerySucceeded for success - onQueryFailed for errors
  clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}

function onQueryFailed(sender, args) {
  //show error message ()stacktrace
  alert('Request failed. ' + args.get_message() + 'n' + args.get_stackTrace());
}

function onQuerySucceeded() {
//show successful message
alert('View successfully changed!');
}
</script>
</code>
Changing existing list views
Comment: I don't want to redirect the user. I just want to change the view even if it changes  for all users.  I have separate function to check for the user's group.
Comment: updated my answer


What is a word or phrase that describes an object whose importance depends on its recentness?

Question: For example, a newspaper. In general, last week's newspaper is much less relevant than today's. I want to use it in a sentence like: "Since newspapers are ____ in nature, it's important to be notified the moment a new issue comes out." Temporal is the only thing I can think of, but not really since I don't want to emphasize the object's impermanence.
Comment: _ephemeral_ is the word.
Comment: @Xann 'Ephemeral' is *a* word, but not a good fit here. I suppose you could say their *value* is ephemeral.. still doesn't seem quite right to me though.
Comment: Go to your local library and ask for the section *Ephemera* -- you'll find the newspapers there.  Vital today, lining the bottom of your budgie's cage tomorrow.
Answer: When English speakers can't think of a single word for something, they sometimes stick words together to make a phrase.  That's the case with time-sensitive, which the Cambridge Dictionary helpfully defines:

time-sensitive
  adjective UK  US

  used to describe a product that has to be delivered by a particular time, or information that is only useful for a particular period:
  We deliver high-value, time-sensitive goods like cars, computers and specialist chemicals.
  time-sensitive documents

The word ephemeral suggested by a commenter conveys the brevity of something's life span, but it fails to deliver an indication of value.
We can raise the stakes on time-sensitive (a newspaper, in the original post) to time-critical (in the case of a shipment of vaccine for an outbreak of gomps in a remote corner of Rumtifoo).
Answer: I see you did mention temporal, the first thing that came my mind was temporal relevance (of the news, I don't think that emphasises the object's impermanence).
You could also borrow the phrase time value from finance (i.e. the 'time value of money' - £1 in your hand today is worth more than the promise of £1 later).
You could riff on that idea without the jargon by talking about newspapers' waning/depreciating relevance.
Another phrase might be 'of the moment' or similar.


Battlefield 3 ''Race''  in ME3 Multiplayer

Question: In the ME3 multiplayer lobby, I've seen some people list Battlefield 3 instead as their race. How do you obtain this? Is there any other perks other than the name change?
Answer: You have to log in to Origin with an account that has an activated Battlefield 3 Online Pass, and the pack is only for the PC and Xbox 360 versions of ME3. From the Mass Effect Wiki:

Battlefield 3 Pack (Free, single-use) - Unlock your Battlefield 3 Limited Edition soldier! A kit containing items with an aesthetic inspired by Battlefield 3. Requires that the player signs in to Mass Effect 3 with an Origin account linked to a Battlefield 3 Online Pass. (PC and Xbox 360 only)

The Battlefield 3 "race" is mostly a Human Soldier with the power Carnage instead of Concussive Shot. Full list of Powers at the Wiki, aside from the obvious cosmetic differences.
Answer: I believe they must have changed or lifted those exclusives, because I have never played any Battlefield and I use a PS3, and I unlocked the Battlefield 3 soldier with a veteran pack yesterday.  I don't see what the big deal is -- it's kind of a mediocre class.


What is best one between JSF and angular for java hibernate,spring,strut application?

Question: I want to develop application using java frameworks(spring,hibernate,strut). This application has large complex operations.I want to know what is the best between JSF and angular? As well as i want reference for compare those  technology
Answer: This is a hugely broad question, but to quickly address a main difference:

JSF is framework for dynamically generating HTML on the server side. There you can dynamically generate HTML elements directly based on your Java objects.
Angular manipulates the HTML on client side. You can have HTML elements reflecting your model in Angular - but these will be javascript objects (JSON).

The two aren't mutually exclusive - for example look at AngularFaces.
It really depends on what you're wanting to do. If your application is fairly static 'load a page, submit a form' then JSF will probably be right for you. If there is lots of clientside interaction with different HTML elements constantly changing, then a framework like Angular or React will be better for you.
Answer: Reading the question, it sounds very loaded for the answer you are seeking. Not to be sarcastic, but to present a simile it sounds like you want to fit a square peg but happen to find only circular or spherical problems.
To read "want to develop application using java frameworks" -- one have to understand why these solutions exist and what they solve compared to competing technology which are better at solving some other niche problems.
To add to the notes presented by dwjohnston, JSF has a 6 stage lifecycle (refer the complete guide for better understanding) that ties the actions on the web UI to data that gets persisted or process that invokes a backend webservice. Compared to the solution that is provided by JavaScript frameworks like Angular, React, Backbone to name a few; serve a problem space where lots of interactions on the Web UI translate to fewer backend process and does not drag down the entire application. To stay concise for the sake of answering the question, you need to approach the problem with a view of  solving rather than looking for problems that can be solved by the solution that you want to be part of.


How do I create a graph that has a continuous axes with matplotlib?

Question: I'm trying to create an interactive graphs. I can't figure out how to plot a quadratic graph that is continuous - as in if you zoom out/move across the axes, the equation is plotted there, not just between 2 x points, so it's continuous.
I've got this so far.
import matplotlib.pyplot as plt

xcoord=[]
ycoord=[]

for x in range(0,10):
    y=(2*x)**2 + 2*x + 4
    xcoord.append(x)
    ycoord.append(y)

plt.plot(xcoord,ycoord)
plt.show()

Answer: Matplotlib is does not plot functions, but rather points. Of course any continuous function can be approximated by points if they are only dense enough.
The problem indeed occurs when zooming into the plot, in which case formerly dense points will spread out and a polygonial structure will be observable. Inversely when zooming out, it may happen that the function has not been evaluated outside a specific range and hence the plot will stay mostly empty.
A solution is to evaluate the function each time the axis limits change, notably on a grid which covers the complete axis range and has as many points as there are pixels. We can find out the number of pixels from the figure size and dpi.
To show the effect, I added a sinusodial function with a low amplitude here.
import numpy as np
import matplotlib.pyplot as plt

func = lambda x: (2*x)**2 + 2*x + -4 + 0.2*np.sin(x*20)

fig, ax = plt.subplots()
ax.axis([-8,8,-100,400])
line, = ax.plot([])

def update(evt=None):
    xmin,xmax = ax.get_xlim()
    npoints = fig.get_size_inches()[0]*fig.dpi
    x = np.linspace(xmin, xmax, npoints)
    y = func(x)
    line.set_data(x,y)
    fig.canvas.draw_idle()

ax.callbacks.connect('xlim_changed', update)
fig.canvas.mpl_connect("resize_event", update)
plt.show()

Answer: If I understand your question, you want to dynamically recalculate the content of the plot (the coordinates) based on the current axis pan / zoom. Doing so requires using event handling to detect a change in axis limits, then recalculate the coordinates with a predefined number of points between these limits, and finally updating the plot accordingly
import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np

def my_func(x):
    return (2 * x) ** 2 + 2 * x + 4

def on_lims_change(axes):
    xmin, xmax = axes.get_xlim()
    new_x = np.linspace(xmin, xmax, 1000)
    new_y = my_func(new_x)
    l.set_data(new_x, new_y)

fig, ax = plt.subplots()
xcoord = np.linspace(0, 10, 1000)
ycoord = my_func(xcoord)
l, = ax.plot(xcoord, ycoord, 'r-')

ax.callbacks.connect('xlim_changed', on_lims_change)
ax.callbacks.connect('ylim_changed', on_lims_change)

on_lims_change(ax)
plt.show()

Credits go to @ImportanceOfBeingErnest for showing how to connect an event handler on changes to the axes limits in this answer
Answer: continuity is hard to replicate, it sounds like what you need is to increase the plot density. Change your loop and use numpy
import numpy as np
numpy.linspace
import matplotlib.pyplot as plt

xcoord=[]
ycoord=[]

for x in np.linspace(0,10,1000):
    y=(2*x)**2 + 2*x + 4
    xcoord.append(x)
    ycoord.append(y)

plt.plot(xcoord,ycoord)
plt.show()

Comment: if using numpy, no need for a loop. `xcoord=np.linspace(0,10,1000)` and `ycoord=(2*xcoord)**2 + 2*xcoord + 4` is enough


Operating system-loader

Question: My question is how operating system loads
 User space application to RAM. I know how
  Bootloader works when we first turn computer on Bios simply reads 512 kb data till aa55 bootloader signature and loads bootloader to ram. Do regular userspace programms are handled in this way? If yes how? Because bootloader activated by bios and how user space program handled by operating system? More specifacally how execv()  load program to RAM and start execution point for user space ?
   Thanks in advance
Comment: Possible duplicate of [How does a loader in operating system work?](http://stackoverflow.com/questions/32688459/how-does-a-loader-in-operating-system-work)
Comment: The BIOS doesn't load 512 kilobytes, but only 512 bytes.
Answer: Userspace programs are not handled like the bios, the Kernel will be involved in running a userspace program.
In general:
When a program is executed in shell, the shell will invoke system calls to create a new task in a new address space, read in the executable binary, and begin executing it.
To understand the details, you need to understand:

The elf format. Of course there are also other formats which can be used in Linux, elf is just the most common one, and a good starting point. Understanding elf will help you understand how the kernel loads the executable binary into memory precisely.
Linux process management; this will help you to understand how a program starts to run.
Reading the related codes in the kernel. fs/exec.c will be of great help.
Answer: The procedure varies among operating systems. Some systems have a background command interpreter that exists through the life of a process and within the process itself. When a program is run, the command interpreter stays in the background (in protected from user mode access). When the program completes, the command interpreter comes to the foreground and can run another program in the same process.
In the Eunuchs-world, the command interpreter is just a user-mode program. Whenever it runs a program it kicks off another process.
Both of these types of systems use a loader to configure the process address space for running a program. The executable file is a set of instructions that define how to lay out the address space,
This is significantly different from a bootloader. A bootloader blindly loads a block of stored data into memory. A program loader contains complex instructions for laying out a process address space that include handling shared libraries and doing address fixups.
Comment: Can you give any example code piece? So i can see how programm inserted to ram ? Thanks

Operating system-loader


What is the difference between Kohana::message and Kohana::config?

Question: I Learning a framework Kohana.
What is difference between Kohana::message and Kohana::config?
They perform the same function.
 Maybe if there is a difference between the concept?
Answer: One is for configuration information. The other is for reusable text: Kohana::message('registration.error.email') could say something like "There is already an account using the email address you entered, an email with instruction on how to reset you password has been sent in case you forgot it.".
Answer: Kohana:message
These are generally used to store messages that will be displayed to the user. For example if you have a method that tries to create a user and it fails, you can get the relevant  you can you may have the following in a User Controller:
$create = $this->create_user($user);

if($create)
{
    // user created
    $message = Kohana::message('user', 'create_success');
}
else
{
    // failed to create user
    $message = Kohana::message('user', 'create_error');
}

Kohana:config
This is used for configuration information such as the hash_method used in auth module and you can access it using Kohana::$config->load('auth.hash_method')


How to partition a training-set when I have a big class imbalance?

Question: In my actual data class A has 90%, class B has 9% and class C has 1% (numbers are made up for sake of simplicity). Now I want to prepare a training set for my classifier (I plan to use Vowpal Wabbit). How should I distribute entries according to classes? Should I maintain the same ratio as in real data or I should distribute entries evenly?
Answer: Answering your second question first:

Should I maintain the same ratio as in real data or I should distribute entries evenly?

In my opnion, it makes sense to maintain the same proportion of classes as in the complete set of data. Typically, there is a reason why this distribution is skewed (e.g., it may be naturally observed in the event being studied) and hence learning in the presence of this skew would help to generalize better to the unseen samples. This would be my suggestion in the general case. Subjectively, things could be different. And, of course, you will then have to be careful about how you evaluate the performance of your classifier. There is literature on how to handle such skewed cases.
Now, to answer your first question:

How should I distribute entries according to classes?

You could use stratified folds to prepare your training sets. This will let you maintain the proportion of the classes in your training folds as in the complete data.
I am not sure if you work with Python, but to get you started, scikit-learn, a popular Python package for machine learning, has this provision for you in sklearn.cross_validation.StratifiedKFold.
Comment: The problem I see here that some classes have rather rare occurrence and I will need very big training set to give them good representation.
Comment: @Andrey, right. In cases where this may be difficult (to get a big training set) or  impossible, one will have to think of feasible ways/work-arounds to deal with it.
Answer: There are several ways to work around class-imbalance. As SPN pointed out , its probably best to maintain the class distribution in your training data as per your real data.
Also want to point another way to doing this: working with a class distribution of 90-9-1 could be a lot trickier than working with 90-10, ie. combining classes B and C and have your classifier work on the "A or not A" classification problem. Then, build a second classifier to classify between B and C, if required. The good thing about working with binary classifiers (2-class) is that there are alternative measures of accuracy (eg. F-measure, adjusted geometric mean (http://www.ncbi.nlm.nih.gov/pubmed/22809416)).


What happens if there was a short circuit fault BEFORE the main circuit breaker?

Question: I haven't studied power systems yet but i keep wondering about that.
What would happen if there was a short circuit fault BEFORE the main circuit breaker(on the grid itself)? what protction is supposed to stop that kind of faults?
Comment: common sense and care?  Home Breakers are rated for 10,000 A surges which can vaporize screwdriver material shorting across the line and return.  Grid current rises by integration very fast with line inductance, so I*t thresholds are for tripping distribution grids are very critical to prevent transformer explosions.
Answer: You can't stop the fault but you can limit the damage.
The distribution transformer will have fuses on the primary (high voltage side) and secondary (low voltage side) to prevent the wires running to your house from vaporizing and to prevent damage to the transformer and disruption to the grid.
Everywhere through the distribution system there will be similar protective devices, they just have to handle more kVA the further you get up in the food chain.
Answer: Depends in what context you call it "main circuit breaker". If you are talking about the main breaker on your household, then the distributor allways installs a protection of their own between your house input and the grid (usually a fuse).
So, the fuse would blow up, and you'd have to call the distributor to come and replace it.
Answer: Distribution transformers have large cylindrical fuses in them.
Sub-stations have fast smart protection gear with breakers and reclosures that must swing wide open to quench the holdoff arc current.
A Power transmission line model appears as follows;

From Telegrapher's Equations a surge impedance can be determined. This is often rated by % per unit.

The short circuit power can be defined by ;

The source end of transmission can look like this with propagation delays;

a sample simulation


If the static port get blocked, and no alternate static air source is fitted, will the transponder keep provide mode C?

Question: If the static port get blocked for any reasons and the aircraft is not fitted with an alternate static source while in Mode C with SSR, will the ATC still get the height information from my transponder?
Comment: Related: https://en.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603
Comment: how does it know that the port is blocked? So I'd say: yes....
Comment: I remember something about transponder with mode C which is mechanically actuated by the altimeter's aneroid capsule so I guess it will give erroneous information. But I will wait an explanation from someone who knows more about this. That's all I've got.
Answer: It will stop reporting correctly as it is connected to the same static air line as the altimeter

The transponder depends on an external altitude encoder to provide the digitized pressure altitude that the transponder needs for its Mode C replies. The encoder is connected the same static air line as the altimeter and is wired electrically to the transponder

However the transponder may not know the port is blocked and will still report the erroneous information it is receiving. If the port is blocked it's pertinent to shut off altitude reporting manually.
Comment: yes if you see the malfunction then shut it off. however in most cases ATC will ask for your altitude when the mode-c altitude does not match your assigned altitude. but you will also have trouble with the main altimeter and airspeed indicator. It may be most noticed with the behavior of the vertical speed indicator. Also most GPSS units have an option to show geometric altitude, which will show gross error in the altimeter, but not reliable for small errors as it is not compensated for pressure variations.
Answer: If the static ports were blocked the mode c transponder would likely still report an altitude based on the static (atmospheric) pressure that was in the system when it became blocked.  But as soon as the aircraft changed altitude or other pressure variations occurred, the mode c altitude report (displayed to ATC), would be erroneous.
From the FAA's AMT Airframe Handbook Volume 2 (full version) (FAA-H-8083-31), volume 10 (link is here)
(emphasis is mine)


Prove that the centroid of $\triangle ABC$ lies on the circle $C_1$

Question: Let $C_1,C_2$ be two concentric circles, the radius of $C_2$ being twice the radius of $C_1$. From a point $P$ on $C_2$ tangents to $C_1$, $PA$ and $PB$, are drawn. Prove that the centroid of $\triangle ABP$ lies on $C_1$. The circles are concentric  thus the equations are $x^2+y^2+2fx+2gy+c_1/c_2=0$. Now I have found $c_2=0$, $c_1=-3r^2$. But I dont think its of any use. Is there any way to prove it.
Answer: Note that if $O$ is the center of the circles, smaller one having radius $r$, then $PO=2r$, $AO=BO=r$.Also, $PB \perp BO$ and $PA \perp AO$. It follows that the $PA=PB$ , and because $PAO$ is a right angles triangle, it follows that $PA^2 = 4r^2-r^2=3r^2$.
Since $PA=PB$, the triangle $PAB$ is an isosceles triangle. Suppose we draw the median from $P$ to $AB$ intersecting at $E$. Note that this line is bisecting $AB$. Furthermore, because $PAB$ is isosceles, this median in particular divides $PAB$ into two congruent triangles $PAE$ and $PBE$ $(PE=PE,PA=PB,AE=BE)$. It follows that this line is a perpendicular bisector of $AB$.
But then, every perpendicular bisector of a chord of a circle passes through the center. It follows that $O$ lies on $PE$.
Let $AE=a,EO=b,PE=c$. The following equations then are true:
$a^2+b^2=r^2$ (From triangle $AOE$)
$a^2+c^2=3r^2$(From triangle $PAE$)
$b+c=2r$ ($OE+PE=PO$)
Solving these equations, we get $c=\frac{3r}{2}$  and $b=\frac{r}{2}$(a doesn't matter).
It's known that the centroid divides medians in the ratio $2:1$. Let the centroid of $PAB$ be $Q$, then this says that $PQ:QE=2:1$. Hence, since $PE=\frac{3r}{2}$, $QE=\frac{r}{2}$. Finally, $QO=QE+EO$ (they are on the same straight line) , hence $QO=r$ and $Q$ lies on the smaller circle.
Please ask if any doubts.
Answer:
The right triangle $\triangle OPA$ has $OP=2OA$, thus $\angle OPA=30^\circ$. Similarly, $\angle OPB=30^\circ$. So $\angle APB=60^\circ$.
Since $PA=PB$, $\triangle PAB$ is an equilateral triangle.
From that fact, there are many ways to draw the conclusion. For example:
Let $G$ be the centroid of $\triangle PAB$, it follows that $\angle AGB=120^\circ$. Thus it lies on the small arc $AB$ of the circle $C_1$.


java.util.zip.ZipException: too many entries in ZIP file

Question: I am trying to write a Java class to extract a large zip file containing ~74000 XML files.  I get the following exception when attempting to unzip it utilizing the java zip library:
java.util.zip.ZipException: too many entries in ZIP file
Unfortunately due to requirements of the project I can not get the zip broken down before it gets to me, and the unzipping process has to be automated (no manual steps).  Is there any way to get around this limitation utilizing java.util.zip or with some 3rd party Java zip library?
Thanks.
Answer: Using ZipInputStream instead of ZipFile should probably do it.
Answer: Using apache IOUtils:
FileInputStream fin = new FileInputStream(zip);
ZipInputStream zin = new ZipInputStream(fin);
ZipEntry ze = null;

while ((ze = zin.getNextEntry()) != null) {
    FileOutputStream fout = new FileOutputStream(new File(
                    outputDirectory, ze.getName()));

    IOUtils.copy(zin, fout);

    IOUtils.closeQuietly(fout);
    zin.closeEntry();
}

IOUtils.closeQuietly(zin);

Answer: The Zip standard supports a max of 65536 entries in a file.
Unless the Java library supports ZIP64 extensions, it won't work properly if you are trying to read or write an archive with 74,000 entries.
Answer: I reworked the method to deal with directory structures more convenient and to zip a whole bunch of targets at once.
Plain files will be added to the root of the zip file, if you pass a directory, the underlying structure will be preserved.
def zip (String zipFile, String [] filesToZip){
    def result = new ZipOutputStream(new FileOutputStream(zipFile))
    result.withStream { zipOutStream ->
        filesToZip.each {fileToZip ->
            ftz = new File(fileToZip)
            if(ftz.isDirectory()){
                pathlength = new File(ftz.absolutePath).parentFile.absolutePath.size()
                ftz.eachFileRecurse {f ->
                    if(!f.isDirectory()) writeZipEntry(f, zipOutStream, f.absolutePath[pathlength..-1])
                }
            }
            else writeZipEntry(ftz, zipOutStream, '')
        }
    }
}

def writeZipEntry(File plainFile, ZipOutputStream zipOutStream, String path) {
    zipOutStream.putNextEntry(new ZipEntry(path+plainFile.name))
    new FileInputStream(plainFile).withStream { inStream ->
        def buffer = new byte[1024]
        def count
        while((count = inStream.read(buffer, 0, 1024)) != -1)
            zipOutStream.write(buffer)
    }
    zipOutStream.closeEntry()
}


Can the color of an object be entangled?

Question: Based on the answer to another question asking "What properties can be entangled?  the answer to the question was "any property".  But with all due respects to the answer,  I must admit I am somewhat confused on the following details.  Must the property perhaps be a quantum number or related to a quantum number in some way? Experiments seem to always want to measure either spin or polarization. But what exactly determines what can be chosen to be entangled?  This is why I chose something that would on the surface be described  as a qualia. ( i.e. An emergent property and not fundamental.)  As for example another emergent property would be "heat". Is there a laundry list of equations perhaps that must be satisfied in order to declare that a property can be entangled? Thank you.
Comment: Do you mean "colour" as in colour charge of quarks?
Comment: Please provide a link to the question you are referring to.
Comment: -1. No research effort.
Answer: You are dealing with elementary particles in entanglement, which don't have that many fundamental properties to begin with.   So if you are asking, to give a silly example I know, can you entangle two colored socks, no.
The people who perform the entanglement experiments need to go to extreme lengths to keep their entangled particles isolated. That is a major problem for them, and for the development of quantum computers also, that is shielding from outside influencs.
Here is a list of quantum numbers and the associated properties they label Quantum Numbers.
Answer: I don't see why the OP's question should be considered silly. And I also don't follow Countto10's claim that two colored socks can't be entangled. Surely any two objects can be entangled. (Note that the OP question is one of principle, not of practice.)
However, I feel the OP's question is even a bit more abstract. He does not seem to be asking whether two objects of different color can be entangled, but rather whether 'redness' can be entangled with 'blueness' (in the same sense that 'upness' can be entangled with 'downness'). More concretely, something like two balls at different locations being entangled with each other, in principle completely indistinguishable except for their color, which is either red or blue. The entanglement would be such that if one is red, the other must be blue and vice versa. In other words, it is the usual Bell pair with `spin' replaced by 'color'.
I see no issue with this set-up. One does have to make clear what one means by 'color'. 'Spin' can be defined in terms of its measurement: it determines how something moves in a magnetic field, say. Similarly 'color' can be defined as the (coherent) light it emits when white light hits the object.
This is determined by the molecules that make up the object. In other words what one conceptually would refer to as an 'entanglement of colors' would come down to an 'entanglement of molecules', which already sounds more 'down-to-earth'-ish (at least for a theoretical physicist). In this precise language it is no longer really a 'qualia' though, so if the OP is unhappy with this interpretation of his question, he can maybe rephrase things.
Comment: +1 for your points. I don't consider the OP's post silly, (and I would avoid answering the question, rather than insult someone who  asked a straightforward question, no matter how basic). I simply meant that **my** example was going to  be silly  as it involved, well socks. I should have spelt out the reasons why anything like a pair of socks could not in practice be entangled, and as you say, distinguished between principle and practice. I thought that to emphasise the care with which entanglement experiments are carried out was enough to make the point.
Comment: @Rubin Verresen    Yes , you picked up on what I was trying to ask. I must admit I asked it rather poorly and can see it caused some consternation. My fault.   I accept your answer and thank you!     As a side note.  You isolated my question to an entanglement of molecules with some specific properties that  give rise to "color".  I am wondering if there is a quantum mechanical limit to how many "qualia" can be entangled at the same time but that is for another time.


Find most frequent element in a list in lisp

Question: I've been searching for a while for a function that does this in (Common) Lisp. Does one already exist, or do I need to code it on my own? To be more specific, I'm looking for a function that if I fed it in something like '(1 2 4 1), it would return 1?
Comment: A very good reference to all the Common Lisp specification is the Hyperspec (http://www.lispworks.com/documentation/HyperSpec/Front/index.htm). You can see all the functions available in a specification conforming implementation.
Answer: You would need to make it yourself. You'll need to keep the count for all the elements, then do a scan through the hash to find which one has the highest frequency.
Of course it could be that more than one has the highest frequency, what then?


Proof of finance when entering the Ukraine as a German citizen

Question: I am planing a trip to Ukraine and read about a proof of finance as an entry restriction for foreigners. The website of the german Auswärtiges Amt is mentioning that since 2013 every non ukrainian citizen visiting Ukraine has to verify that she/he has an income of 2300€ a month or at least 80€ per day in Ukraine + 400€.
I would like to know how and how strict these conditions are checked when visiting Ukraine (I am german citizen).
Comment: what's your country of citizenship?
Comment: @JonathanReez I am german. Added to the Question.
Comment: The website that you referring to actually has the answer: The "Auswärtiges Amt" does not have any experience on how these rules are actually implemented in practice. Since the rules are 1.5 years old, this tells you that they are almost never enforced. Also, the list of suitable documents even counts tickets, hotel reservations, and credit cards. I would take a printout of my account statement just to be on the very safe side. Finally, you don't need an income of 2300€ but rather 2300€ per month of stay (according to the page). That's quite a big difference for most travellers.
Comment: I never heard of solvency check at Ukrainian ports of entry. Not breaking 90-day rule with a visa-free travel is important, but not the financial part: you are highly unlikely to be ever asked about funds for your travel.
Answer: I was in the Ukraine in May traveling on a Western European passport.
Upon entry, not a single question was asked. Not even purpose of visit or which regions I would visit. I simply got stamped in and that was that.
Based on this experience, I assume that it is not generally enforced and rarely checked. Probably they start asking this kind of things only when some red flags are raised. I was not even aware of the requirement and did not have the documentation on me to prove my financial situation.
Comment: Summer 2014, USA passport, same experience. Don't think the border guard said a word.
Comment: Turned out that it is exactly like this. Not a single question was asked.


How can I use a keyboard shortcut to go to my Dropbox folder

Question: How can I change the Finder keyboard shortcut command + shift + D to open my Dropbox folder instead of the Desktop folder.
Comment: I like command-shift-d for desktop, I'm thinking command-shift-x for Dropbox.
Answer: System Preferences > Keyboard > Keyboard Shortcuts > select Application Shortcuts in the left column > click the "+" button > Application = Finder, Menu Title = Dropbox, Keyboard Shortcut = whatever you like > click Add
test it out. worked great for me from Finder
Note that this uses the Finder's "Go to > Recent Folders" Submenu. If the Folder isn´t in the List (and there's no way to keep it there), you won't be able to jump to it.
Answer: I can get you most of the way there, but I'm going to say straight off that I don't know how to hijack the shift-cmd-D shortcut.  However, if you're willing to settle for a different shortcut...

Open Automator
Create a new Service
Change the service to receive "no input" in "Finder"
Drag in the "Get Specified Finder Items" action
Add a new path to your Dropbox folder in this action
Drag in the "Open Finder Items" action
Save as something like "Open Dropbox"

It should look like this:

Open System Preferences
Select "Keyboard"
Select "Keyboard Shortcuts"
Select "Services"
Scroll down to the bottom and select your "Open Dropbox" service
Click the "add shortcut" button to specify a new shortcut

I tried to come up with a way to override the shortcut for the Desktop menu item, but I was unable to do so.
So this will get you a hotkey to open your Dropbox folder when you're in the Finder, but it won't be via shift-cmd-D.
Comment: This is good, for sure, however will it work from any finder window such as when I'm saving a file?
Answer: here's a method that I implemented that allowed opening the Dropbox folder from within any application (well, it gets called by a Terminal session from the Finder).
This does not however, automatically switch to the Dropbox folder while in the middle of a application dialog box;  it simply opens up the Dropbox folder in the event you need to look into or open something within the Dropbox folder.  To access the Dropbox folder from an application dialog box, you can drag the Dropbox folder into the "Favorites" section of the application save/open dialog box to access it within one click.
Ok, if you're still interested in a hot-key anyway to access the dropbox folder,
here's how to do it:

Open Automator: Cmd-Spacebar, type in Automator.
Select Service, click Choose
Modify "Service receives selected [text] in [any application]" to:  "Service receives [no input] in [any application]"
Select the action "Run Shell Script" under Utilities, drag it over to the right pane.
Change the "cat" command to "open ~/Dropbox".  If your Dropbox folder is located somewhere else, please modify the pah accordingly.
Save as "Open Dropbox Folder"
Open System Preferences: Cmd-Spacebar, type in System Preferences
Navigate to Keyboard -> Shortcuts
Scroll down to General
Ensure the checkbox for "Open Dropbox Folder" is checked (enabled).
Choose the Keystroke combination to open the Dropbox folder.
NOTE:  If you choose Option-Cmd-D, you may need to disable "Turn Dock Hiding On/Off" in the Launchpad  & Dock section.

Enjoy!
Answer: Use Spark to run an AppleScript:
<code>tell application "Finder"
    open ((home as text) & "Dropbox")
end tell
</code>
In Spark, go to File>New Hotkey>AppleScript and set your settings as such:

(You can also use Spark to run a shell script, but I'd recommend using this method, as a shell script is a bit more complicated)
Answer: Lazier-than-creating-an-Automator-service solution:
1) Open "System Preferences / General", under "Recent items", choose anything other than "None".
2) Open "System Prefs / Keyboard / Shortcuts / App Shortcuts", click "+", choose "Application: Finder", enter "Menu Title: Dropbox", and "Keyboard Shortcut: [whatever key combination you like here, I typed commandshiftx]".
3) Open Finder, visit your Dropbox folder. Your folder and its new shortcut are now listed in Finder's menubar under "Go / Recent Folders".
Assuming you visit your Dropbox folder frequently enough, this will work in Finder navigation. It doesn't work within other app's "Save" or "Open" dialogs, unfortunately.


What kinds of web applications need dynamic packet filtering or deep packet inspection

Question: I have some customers requesting that we put apply DPI or dynamic packet filtering in front of our web server.  For the simplicity of my service, I'm feeling like this is over kill.  What kinds of web apps really benefit from DPI / DPF as opposed to just building in adequate protections at the web app level ie SQL injection prevention, etc?
Answer: I'd ask your customers about what are they looking for in network packets and how deep they want to inspect them.
If they want inspection at 4-th level - you can setup free snort/suricata.
If they want it at level 7 - there are plenty of choices from free mod_security to cloud-based WAFs.
DPI as it meant to be is very resource-intencive, and mostly used by ISPs or large enterprises.
Comment: A web app firewall is what I would Initially recommend too. It's pretty easy to setup, and catches a lot of low hanging fruit.


How do you send data to the Detail View from Master View in iOS 5 iPad app?

Question: I am trying to make an extremely simple app that using a split view.  I would like a list of checklists on the left that you can click on and display more detailed information on the right side of the screen.  It seems that split view is the right view controller but I am having some trouble.  I am very new to iOS programming.  I understand how to add items to the Master View on the left using the inspector options.  I am not using arrays to populate my cells in Master View.  I simply added more cells through inspector and just renamed the label of each.  I do not however understand how to connect each cell with the Detail View.  I have searched far and wide on the internet and come up with nothing.  All information is outdated and doesn't work for Xcode 4.2 or iOS 5.  If you have any information at all please help.  I am a total noob with this so please be as descriptive and basic as possible.  Thank you so much!
Answer: Look at the MultipleDetailsViews.xcodeproj provided by Apple. It supports iOS 5 and also runs fine on iOS 6.


Identify 16s rRNA in metagenomes

Question: I have a database of projects downloaded from EBI metagenomes. These are fasta files containing sequence reads and have undergone basic processing (repeat masking, length cutoff - 100 etc) I want to extract sequences that are 16s reads from here. Would anybody know of good tools that do this function?
Thank you for your help!
Comment: you should ask biostar http://www.biostars.org
Answer: We (EBI metagenomics) will be releasing a new feature soon that does just that, so if you can wait there will be an option to download sequences matching the 16S gene model. We also intend to provide taxonomic trees based on those sequences. The selection of 16S reads will be done using rRNASelector, which is an open source software tool that you can find on the internet. Hope that helps and keep an eye on EBI metagenomics (https://www.ebi.ac.uk/metagenomics) .
Thanks.
Answer: You can use our tool called C16S (developed by Biosciences R&D, TCS Innovation Labs).
C16S: A 16S rDNA classification algorithm that uses genus-specific Hidden Markov Models (HMMs) for taxonomic classification of 16S rDNA sequences. In order to achieve high levels of accuracy, the C16S classifier incorporates a series of steps which attempt to refine the final assignment of the 16S rDNA fragment by taking into account the quality of the HMM alignment.
LINK : http://metagenomics.atc.tcs.com/C16S/

Identify 16s rRNA in metagenomes