Salary and Rank Discrepency: assistant profs with better records than associates in the same dept

Question: Is there anything to be done when a department has hot young assistant professors with much stronger research records (in books and peer-reviewed publications) than the associate professors? Must the assistant professors just accept that they are less well ranked and less well paid than associates who have been less productive?
Comment: Not all assistant professors are less well paid than associate professors...
Comment: Get to working on their promotions?
Comment: Prepare to watch the assistants leave for tenured positions elsewhere while your department collapses in on itself due to attrition?
Comment: To expand on StrongBad's point, salary inversion often refers to what happens when assistant professors are hired at a higher salary than existing associate professors. This can happen if the university changes its salary structure (for example to try to attract better faculty.) It is not uncommon for this to happen.
Comment: Stronger research records is one thing. Funding might be another. Universities need people who attract funding (NSF, Horizon 2020 for Europe) probably more than paper-producing machines.
Comment: That is not how the term salary inversion is typically used. I have never heard the term rank inversion, but that might be a reasonable use.
Comment: If the assistant professors are unhappy, they should apply for and get associate professor offers from another, more prestigious, university. Then the department will have to respond if it wants to keep them.
Comment: Most of the assistants also have more external grant money than the associates, so that's not the explanation. Working on their promotions sounds reasonable, but oddly enough the associates don't think there's a problem and so aren't motivated to do anything about it. And, the assistants are relatively powerless.
Comment: The salary inversion I'm talking about is in the opposite direction. The associates are better paid than the assistants, even though many (not all) of the assistants have more publications and more grant money than the associates. I suspect Bill Barth is correct, and the assistants will vote with their feet.
Comment: I agree with @StrongBad: you are using the term "salary inversion" in precisely the opposite of the usual manner.  That's pretty confusing.  Underneath that I see a reasonable question, so I suggest you edit to clarify.
Comment: Do you have a suggestion for a better word? Inequity seems accurate, but perhaps unnecessarily inflammatory.
Comment: **Differential**?  **Discrepancy**?
Answer: Position in a university, and consequently salary, is not simply a function of being "hot and young", grant funding, and publications. But there are many other factors you may be missing. For example, the associate professors in your department may be teaching larger classes (under the assumption that the department tries to give the assistants smaller classes while they build a resume for their tenure decision); they may also, with more experience, be better teachers. And they will almost certainly have far higher service loads -- sitting on committees, mentoring, reviewing duties, etc. All of these are things that are valuable to a department and that is worth a certain amount of salary. But it's hardly visible from the outside, even though it definitely diminishes your ability to do research and publish a lot.
Finally, the associate professors have one less promotion to look forward to, and consequently a lower salary potential. For example, an assistant professor paid 5% less than an associate will earn 5% more after promotion, which translates into a quite significant sum over the remaining work life.
I do get your point, and there definitely are departments that have significantly improved and where the young crop is better than the old, and should expect to be paid better when comparing at the same stage in their careers. But it's hard to determine a "fair salary" between different ranks if all you reduce things to is grants & publications.
Answer: You seem to think that 'top' assistant professors carry the whole university.  They are one of many variables that play a role in the running and success of a university.  Who do you think pay the salary of professors? Hint: it's not high quality papers.  Answer: coursework students.  How do you get coursework students? for one, you have to teach well, have a well-run university; good admin, programs, reputation for teaching, community engagement, getting jobs, etc.  These 'other' people you seem to think the ass/prof are better than actually created the environment that allow the ass/prof to flourish.  Who do you think should get the higher pay?  The leach (newbie) or the host?
Comment: You seem to think that the assistant profs aren't teaching the 800-person service classes. You think wrong. In fact, the person I'm most thinking of (the assistant with the strongest research record) also teaches the dept's largest class. And teaches it every semester because its the dept's major service class. It is certainly true, however, that the associates carry more of the administrative burden. But, then this same person asked for consideration for early tenure (thereby opening them up to pick up some of that administrative burden), they were told they had to wait their turn...
Comment: ...and that it didn't matter how good their record was. They just had to wait. That is the source of the intra-departmental frustration for that the assistant, as well as a few others who (having watched his request) haven't even asked.


Why can't I series 5 D Cell Batteries to achieve 7.4 volts?

Question: I appreciate this site that is allowing me to get an answer to a phenomena I am witnessing.  I'm trying to series 5- D Cell Batteries. However I cannot make it completely through because the middle battery refuses to pass the voltage through.  I can hold the wire from the negative post of the second battery to the positive post of the third battery and get 7.4 (plus or minus) on the multimeter.  However, when I solder the wire in place the total voltage will disappear and only three batteries on one side will complete a circuit of 4.5 volts, while the other two batteries complete a circuit of 3.3 volts. I am baffled by this.  Is my body (finger) touching the wire to the terminal acting as a capacitor allowing the voltage to series thru?   It almost seems that the action of soldering is shorting out the whole series.  Could someone shed some light on this?
Comment: You might be better asking on the [Electrical Engineering Stack exchange](http://electronics.stackexchange.com/)
Comment: Are you soldering directly to a battery terminal?  That would be difficult to do reliably.
Answer: If you are seeing 4.5 volts across three batteries and 3.3 volts across two others, then the join you think you made is not a join.
There is a common thing in electronics called a "cold solder joint". It usually happens when your solder is not quite hot enough when it touches the metallic surface - just the kind of thing that happens when you solder to a large piece of metal such as a battery.
Most likely, if you could just "unsolder" the wire, give the surface contact of the battery a good scratching with fine sand paper, let your iron get really hot and allow a small dab of solder to flow onto the battery with some solder flux, then you will get contact and the circuit will work as you expect.
As an aside, the way you formulate your problem suggests you could use a bit of a primer on batteries, voltage, current, shorting, capacitors, etc. I may expand this answer later if you would appreciate the additional info. For now, see if my suggestion explains your observation - and whether the proposed fix works.
Comment: It's a valid comment on your part but I've soldered thousands of components.  I pre-soldered the tip of the battery with a very hot iron (40w) so that I knew the solder would adhere and it would heat up the immediate area very quickly so as not to harm the interior of the battery.  Then I tinned the end of the wire so I could attach it very quickly.  I can touch the wire to the solder and get my full voltage.  As soon as I 'sink' the wire tip into the solder with heat the voltage disappears.  The 4.5 volts from the 3 batts in series simply will not join the 3.2 on the other side.
Comment: Hmmmm. What happens if you switch the batteries around. In other words - right now you have a "bad" connection with 1-2 not connecting with 3-4-5. What if you made the connection 3-4-5-1-2 and measured from the top of 3 to the bottom of 2?
Answer: You should not sold components that aren't design to be solded. Most batteries have an antioxide surface treatment that make it bad for solding (I can tell for experience). Also, when solding, is the surface which has to reach certain temperature; and that is not recommended in general for batteries.
So, if it's a good solder, you may had damaged the battery, if you don't warm it enough, you may have a "cold solder joint" as @Floris said.
The correct use of D cell type batteries is with the appropiate battery holder, that you do can sold. Also, then you can check if there is a solding fail, or a battery fail.
Example:


Describing FM inductors

Question: Why, when providing FM radio designs, do people use physical parameters instead of electrical? I.E. 2 turns, 20awg, 2cm dia.
Comment: When starting with basic electronics, I've always wondered this myself.
Answer: These are probably very low inductance coils that would not be readily avialble commercially, so the user will have to wind his own, so providing the dimensions is more appropriate than providing inductance (and the designer may not know the inductance anyway).
Answer: Often times these plans for receivers used lower value coils that most parts houses wouldn't carry.  This meant that the user would need to make them himself.  About 99% of the time, the user didn't even know what inductance was, so specifying mechanical specs was easier for the user to interpret, and gave them an idea of what they needed.
About 5 years ago (age 11) I got my first soldering iron and a kit like this.  At that point I had no inkling as to what inductance was, and just barely understood DC resistance and the effect of capacitors on a DC source (as well as how various components behave in parallel/series but that's off topic).  Even if I did know, I would have needed to buy more equipment than I would know what to do with in order to test to make sure I got the right value.  At that point, mechanical specs were simply simpler for me.
In short, KISS.  Keep It Simple SnapCircuits!
Answer: Many readers do not have the skill set to implement design criterion into physical reality. When I first started out, I was so appreciative of this kind of information. I simply didn't have the skills to apply mathematical information into physical implementation. Also, having a KNOWN solution for the circuit gave me the confidence to move forward. Some "Guru" who says use this gauge and this number of turns helped me to make the circuit to work. I know my answer here is short and sweet,  but in reality when providing information to others, you do need to take into account that you might be speaking to an audience from beginner hobbyist all the way to a PhD. Those who DO understand have a starting point.

Describing FM inductors


How can we ensure security and integrity of data stored in MongoDB?

Question: Since MongoDB lacks support of transactions how one can ensure consistency of data stored in MongoDB database?
Answer: You are mixing concepts here. Transactions are related to atomicity and guarantee that multiple operations are either executed as a whole or not at all.
Consistency, however is (simplified) the guarantee that after each successful transaction or operation applied, the database is in a a valid, usable state.
An example

Note This example is simplified for the sake of understandability.

Often people say that you can not use MongoDB for financial operations such as account balancing, since it lacks transactions. They could not be farer from the truth.
Take a simple example of two users, each with an account:
{
  _id:"act1",
  owner: "Foo Bar"
},
{
  _id: "act2",
  owner: "Bar Baz"
}

And now, we have a collection we call "transfers". Each of our accounts get $100.00 from an outside source:
db.transfers.insert({from:"Scroogey", to:"act1", amount: 100.00, date: new ISODate()})
db.transfers.insert({from:"Scroogey", to:"act2", amount: 100.00 , date: new ISODate()}})

Now, how do we get the balance of our two accounts? Say Foo Bar wants to check his balance. We have to do an aggregation for that:
db.transfers.aggregate([
  { $match:{ $or:[ { from:"act1" },{ to:"act1" } ]}},
  { $sort:{ date:1 }},
  { $group:{
    _id:"act1",
    balance:{
      $sum:{
        $cond:[
          { $eq: [ "$to", "act1" ] },
          "$amount",
          {$multiply:["$amount",-1]}
        ]}
      }
    }
  }
])

Which gives us the correct value when run against transfers:
{ "_id" : "act1", "balance" : 100 }

So far, so good. So how does this relate to atomicity and consistency?

In MongoDB, a write operation is atomic on the level of a single document, even if the operation modifies multiple embedded documents within a single document.

So if we insert a document into the transfers collection, we achieve what we want: atomic transfers from and to accounts. Say Foo Bar wants to send Bar Baz $20.25:
db.transfers.insert({from:"act1",to:"act2", amount: 20.25, date: new ISODate()})

Atomic and consistent. Now, if we run our aggregation again, we get the correct result:
{ "_id" : "act1", "balance" : 79.75 }

If Bar Baz checks his account
db.transfers.aggregate([
  { $match:{ $or:[ { from:"act2" },{ to:"act2" } ]}},
  { $sort:{ date:1 }},
  { $group:{
    _id:"act2",
    balance:{
      $sum:{
        $cond:[
          { $eq: [ "$to", "act2" ] },
          "$amount",
          {$multiply:["$amount",-1]}
        ]}
      }
    }
  }
])

he sees the correct value, too:
{ "_id" : "act2", "balance" : 120.25 }

We have an atomic system to do account balancing without transactions! And still we have a log of all transfers from and to an account which you need anyway. We just use it differently.
There is another way to do it
There is a way to achieve multi-document atomicity from the applications point of view, called Two-Phase-Commits.
Basically, it is an extension of the above. You'd have a transaction collection, in which pending operations are documented. Only if all operations are done successful, the transaction is marked as committed. There are various rollback scenarios. This is definetly more work than doing it like documented above, and should only be considered in case the data model can not be designed for the according use case. That would be the case when dealing with legacy systems, for example, in which you want to add features which would rely on transactions.
Basically you move the transaction logic from the DBMS to the application. This is not necessarily as disadvantage, since control over the various stages of a transaction which is supposed to be committed is much more granular.
Conclusion
As we have seen, there are not transactions. With careful data modeling and a bit of knowledge about the inner workings and tools provided by MongoDB, there is hardly any use case that can not be implemented with MongoDB. It might not be the best tool for any use case, however, and you should choose your persistence system carefully.
If you really need transactions, use the Two-Phase-Commit approach.
Comment: This answer does not address the concern of the original question. In terms of  your example, what the OP is asking for is - when we update the bank account balances, can we guarantee they are always correct on both ends, i.e. the receiver will have $100 more and the sender $100 less, or if the txn fails, neither receiver nor sender will have their balance changed? THAT is what is being asked for and - let's be straight here - that is what MongoDB CANNOT guarantee. No bank will handle balances by endlessly aggregating.
Comment: @nepdev Have you actually read my example. Yes, the balance is guaranteed to be correct. And as for aggregations: How do you think interbank transactions are done?
Answer: By-and-large, you can't. Mongo offers atomic actions per document ie a single document will be successfully written or rolled back. There is no way (as of v3.2) to ensure a set of documents will be all written or all rolled back. Document self-consistentcy can be built into the JSON written. Coming from a relational point of view, think of it like a widely denormalised DB with READ UNCOMMITTED isolation level. Even with the same structure, values types can be ingested differently. The value 2.0 and "2.0" are not the same, neither are "FooBar" and "FoObAr".
V3.2 introduces document validation so you now have some guarantee that some parts of some documents have a certain structure. The very nature of schema-dynamic DBMS, however, means it is possible to insert JSON that reads like a cake recipe into a collection called "SharePrice." Good specs and code reviews are tools to address this.
All software sits in a niche. MongoDB as well, as do Oracle, SQL Server and the rest. With each DBMS, you gain a little and lose a little. Understanding and balance is the key, I believe.
Some further thoughts at this answer.
Comment: I dare to object, slightly. With careful data modeling leveraging the fact that document operations are atomic, most use cases can be covered by documenting states or transitions at a certain points in time. As you have stated in one of your answers, there is always the possibility of a 2pc. So in general and by large, I'd say it is relatively easy to be atomic for most use cases. Just not as straightforward as with other DBMS.


Could a plant capture a person?

Question: Could a plant, with the right adaptations, have the right speed and strength to capture an unprepared human without harming them? The plants would be bound by real rules of biology, and couldn't use muscles or other traits exclusive to groups other than plants. The plant would also be capturing the humans with a vine-like structure that coils around the victim
Comment: I find it unlikely you could do it with vines and be able to restrain a strong adult while not harming a kid when that trap springs. But if thorns are acceptable as well, it is pretty trivial to restrain humans yet be mostly harmless.
Comment: I am unsure: Does the answer need vines, or is that an example? Also, what are the humans expected to carry by ways of tools, and: how long do they have to be restrained to count as captured?
Comment: I think some tangled vines with thorns would already do the trick, no? They would not be hunting humans, and they would not capture everyone, but they might still hold the ocasional unlucky wanderer.
Comment: Answer in a comment: ...as long as it is named [Audrey II](https://www.imdb.com/title/tt0091419/)
Comment: Just ask anyone who has tried to prune a large rose bush :-)
Comment: Ever tried to pick raspberries? Or walk through a field of thistles or cocklebur? Plants don't need speed, muscles, or vines/tentacles to trap a person or animal.
Answer: Trap and Poison:
If you want to catch something the size and skill of a human, then NOT harm them you've got logic issues, since some benefit needs to come to a plant. You'll need to explain why a plant would have a system for capturing humans unharmed. But once you get past that, I'd suggest a few mechanisms that work well by themselves or in combination.
First, your plant produces a fruit that is a powerful tranquilizer - possibly a pleasurable or addictive one. Now, depending on how you define capture and the timeframe over which you want to capture them, they are captured short-term (knocked out) or long-term (they wake up and REALLY want more of the fruit, despite it knocking them out).the person spends all their time passed out under the tree. The justification here is that perhaps the tranquilizer is fatal to other species that die and decompose under the plant, OR that the tranquilized animal is killed by predators (who are possibly ALSO tranquilized and killed by yet other predators, leading to a La Brea-type situation with lots of decaying animals.

If you want a vine-type mechanism, then the vine is coated in the tranquilizer, and the tranquilizer induces a craving to wrap the vines around themselves or cuddle up into the vines. The person is then self-capturing!
Another variation on this theme is that the plant relies on monkeys to carry pollen from tree to tree, and humans are close enough to monkeys to be susceptible to the tree's lure for the monkeys. The monkeys eat fruit from one plant, then are compelled to look for more in another tree. The tree protects it's addictive fruit inside a net of vines to keep other less driven animals out (and the monkeys know how to get in and out). Humans, however, force their way frantically into the net to get the fruit (once they have tasted it) and are trapped. This still works for the plant - the human carefully gets fruit from plant A, along with pollen, is instantly addicted, and seeks out tree B where they get more fruit, deposit pollen, and become hopelessly trapped.

Another effective way a plant could capture a human-sized animal is if the root growth created a shaft down into the ground or into a grown structure that functions as a pit. When big enough, a thin covering over the "pit" is thinned enough to allow a human to be lured to the pit (with fruit, fake treasure, or whatever) and the funnel-shaped pit then wedges the human into an ever-narrowing hole. Directional spikes wedge the human in so they can't extract themselves.

Ideally, the pit is lined with drugged thorns so the human that falls down it is tranquilized to fall into a deep slumber and not resist. Then the plant can hold the person there indefinitely for whatever nefarious reason an author can have (since plants obviously don't think... Or do they?) If it has to be vines, then the pit is lined with vines that swell with fluids when touched. The vines swell and pressure-tighten, with more swelling the more the human resists.

A spring-loaded (the spring being a branch) loop snare could be grown, with a lowering branch trailing a network of roots to hold it in place, then an appropriate trigger causing the loop snare to pull tight around a human's limb. The tranquilizer then numbs the person unconscious, allowing them to be held indefinitely.
Comment: Very good point about the need for evolutionary reasons behind it - OP wants the plant to be "bound by real rules of biology" and evolution the most important. --- Though it does not need a reason to for capturing humans unharmed, it just needs a reason for the apparatus to do so, capture might be incidental
Comment: "If you want to catch something the size and skill of a human, then NOT harm them you've got logic issues, since some benefit needs to come to a plant" not necessarily, and perhaps not within the OPS vision. The flora could be alien in origin, or the humans crash landed/colonizing another planet. The flora could have evolved to trap and digest native fauna, and in doing so would perhaps use enzymes, etc, not harmful to humans. A trapped human might be indirectly killed via starvation, but not necessarily directly killed through digestion.
Comment: @CGCampbell I'm saying the causation for evolving such mechanisms is highly relevant to how it should be carried out. Systems evolve together to deliver outcomes. I need to follow the logic for it to make sense.
Answer:
The plants would be bound by real rules of biology, and couldn't use muscles or other traits exclusive to groups other than plants.

Direct attack is less likely at human size and reaction speed, but you can use the idea of traps.

I remember I saw something like this in that documentary... what's it name?... something like Harry Potter - except they stepped onto a tangle of vines or roots that shifted beneath them. I can't remember if that happened before or after they played some kind of weird chess.

with "gravity assist" the things can go quite fast - like a mass of vines clinging up from  the lower branches of the trees by tendrils, tendrils that give way when the prey is well under and so bury the pray in the tangle of vines dropping from above.

then World's Biggest Carnivorous Plant Catches Whole Sheep! - (well, not quite, it's a sheep that got its wool tangled in brumbles. But a plant doing this way will have chances at the nitrogen locked into those unfortunate proteins). You can use the idea having a plant reorient its thorns (or spawning then over minutes) to make the escape impossible for any prey that got far enough inside of what looked like an innocuous bush.

Once the prey is immobilized, vine coiling and the other horrors can take their natural course at leisure.
Note the first two potentially match the requirement of "capture a human without harming them"
Comment: The plant you're thinking of from Harry Potter was called "Devil's Snare" - it appears at the end of the first book (Philospher's Stone) before the giant chess set.
Answer:
Possibly stretching the definition of capture a bit here, but maybe the plant has absolutely no interest in capturing humans, it just happens to do so, by constraining them to be within a certain radius. The plant produces a toxin that knocks out some endocrinal capability of the humans, and at the same time produces a substance that is metabolized into a working analogue of the, now missing, endocrinally produced substance. The humans will have to stay near the plant (the substance breaks down easily, and has to be ingested from living plant tissue), or they die. Depending on the substance in question, this might be something that is needed every hour, or once a month, thus giving a wide range of radii to choose from. - If the answer needs vines, the human might need to wrap themselves in living vines to take up the vital substance transdermally.

A plant may have evolved to quickly cover and absorb carcasses, masking the smell, deterring scavengers, perhaps working in concert with a fungus? The plant would grow by spreading their roots, being visible topside only by a few blades of grasslike leaves. As soon as carrion is detected by the leaves, the plant digs into its potato-like subterranean stores and kicks into overdrive, covering the carrion in vines and thistles, releasing substances to help the fungus grow (the fungus will help break down the carrion for ease of uptake). The vines harden quickly, effectively encasing the carrion in a cage (So no big scavengers can rob the plant of its prize). All the tasty nutrients get distributed and stored in the root network. Now, if a blind-drunk human should happen to sleep off their intoxication, they might find themselves in a pickle (literally) the next day. Their immune system will fight the fungus, resulting in nothing more than a rash and a cough, but the vines will lock them in place regardless.
Answer: Very strong vines with an exceptionally sticky adhesive could work. Something similar to sun dew plants.
For some reason I am reminded of The Day of the Triffids .
Answer: How "unharmed" do you want? I'm going for "alive".
Thorns.
Brambles are extremely dense, and at the right stage in their growth very strong. As anyone who has gone blackberrying can attest, the thorns are also lethally sharp and can feel strong enough to pull your skin off.
A bush can immobilise a grown sheep when the wool gets tangled, leading this farmer to theorise that they are actually carnivorous and fertilising themselves with decaying sheep: https://www.youtube.com/watch?v=RuzLXxbGc4c
So, a large tough dense bramble, equipped with some kind of Venus Fly Trap style motion trigger to close the branches; the more you struggle the tighter they close.
They are tough to break anyway, your motion would be restricted, and every move you make would be extremely painful, but would probably not kill you.
EDIT: Thinking on this a bit more, the trigger shoots could be away from the thorny branches, on suckers that spread over the ground. Pushing through a dense forest, your hero finds a sort of tunnel where the going is a bit easier. As he walks on through it, he fails to notice the surrounding undergrowth closing in, until SHOOMP! like a Venus Fly Trap, it all closes up.
This behaviour could evolve quite nicely over the normal millions of years as a means of catching any large animal; however, with humans' greater intelligence, very few of them are then digested.
Answer: You might consider Drosera capensis, also known as Cape sundew.
This plant has long and thin leaves, covered with small sticky tentacles.
The leaves curl up to entrap anything that gets stuck to them.

A larger version could have a burr-like surface to further entangle the human's clothing, delaying extraction and giving time for the leaves to curl.
As someone that recently hiked through some brush, I can testify that it is easy to get trapped in vines, even without any sticky mechanism.
It was easy enough to get out again, but it took significant time, and time is what is needed here.
The plant wouldn't even need to be huge, using a single leaf to make the capture.
A struggling human could be trapped by multiple leaves, each of which need be only large enough to wrap around an arm or leg.
Once the hands are immobilized, it's game over.
See: Best of Sundew Timelapses Compilation - YouTube

Could a plant capture a person?


Silicone caulk for shower and tub?

Question: I am about to seal the gap between my tub and the wall tile with caulk (it was originally grout which cracked so I chiseled out what I could). I was planning to use silicone caulk (GE II), but a contractor suggested that pure silicone is not ideal since all caulk will eventually need to be removed and replaced and silicone is very difficult to remove. There's some logic to this, so I'm wondering - is he right? If so, what kind of caulk should I use?
Comment: With all respect, a good caulk needs to be hard to remove. If it was easy to remove, it would be easy for water to get around.  As a note, when you caulk the tub, fill it with water, that way the caulk will compress when empty and not stretch when full
Comment: Contrary to [popular opinion](http://diy.stackexchange.com/questions/25404/should-i-use-caulk-or-grout-between-the-edge-of-a-tiled-bathroom-floor-and-the-w) seen here, [I'd use grout](http://diy.stackexchange.com/questions/61863/what-is-best-caulk-for-a-3-8-wide-x-1-deep-gap-between-a-shower-floor-and-wall/61917#61917).
Comment: @Mazura Thanks for the feedback. Does it depend on the size of the gap? Here are a few pics (you can still see some of the original grout in places where it couldn't easily be chiseled out): http://i.imgur.com/QQrsDe6.jpg    http://i.imgur.com/SmJuPqv.jpg
Comment: I'm getting ready to rip out some moldy caulk and contemplating grouting it instead and I'd love to know what route you took and how it's holding up.
Comment: @Amanda - I ended up grouting and it's held up fairly well, though there are some hairline cracks in a few places. I suspect grout is always going to be susceptible to cracking there since the tub may flex or move a bit relative to the tile since they're not attached to each other. That said, a quick smear of grout over the crack would fix it up pretty easily and I haven't had to deal with any mold in 2+ years.
Answer: That gap is to small. Push really hard with the float to completely fill it with grout, giving it one more shot; next time caulk it. Caulked tub surrounds are one of my pet peeves; I'm the one who gets to scrape that mess out.
Whether grout or caulk, I like Some Guy's advice: prestress the tub by filling it with water as you work.
Comment: How long should I leave the tub filled with water once I apply the grout?
Comment: @Jonathan 24 hours minimum, 72 would be better. -The cure time before sealing the grout; whatever the bag says, you can't use it until then anyway. I said I liked the advice; not that I've ever done it. Ask Dude ;)
Comment: The grout is in! Hopefully it will dry so I can get it sealed before our guests get here this weekend. Thanks for your answer.
Answer: Whether it is hard or easy to remove is really not that important, when it comes to choosing materials for this type of operations. One other thing is far more important: Silicone is organic matter, and like anything organic it disintegrates, especially in rooms like bathroom, which are humid. You should use grouting materials, same (if possible) like you have used for ceramic tiles.

Silicone caulk for shower and tub?


Is there any discrepency on Confirmations?

Question: Is there ever a situation where some bitcoin client thinks a transaction has 3 confirmations and another bitcoin client (or website) thinks a transaction has 4 confirmations, for example?
Answer: Yes, there are a few different ways this can happen, and in nearly all instances this occurring is of little significance.
First the most common scenario where that happens: When a client receives a block it first will verify the block before relaying it.  A node that performs this slowly (especially if running pre-v0.8 software) may be many seconds behind other nodes.   So while one node might verify a block and increment the number of confirmations for a transaction, another node would still be working on verifying it and would show one fewer confirmations.   Within seconds the count should become equal for the transaction on both nodes.
Another scenario is much more rare -- where the blockchain has forked, and a transaction will show a number of confirmations that varies between the count on one side of the fork versus the number of confirmations on the other side.  This scenario actually happened on March 11th, 2013 where nodes running the v0.8 client would show a transaction as having a certain number of confirmations and at the same time a node running a pre-v0.8 client might show a lower number of confirmations.  When the forks converged, after the pre-v0.8 side attained "longest chain" status, both client versions then displayed the same count.
The possibility of there being a problem exists where there are several confirmations showing for a transaction on one node but no confirmations on another.  This could mean the funds for the transaction could be vulnerable to a double spend attack, or that such an attack had already occurred. But the scenario you describe, with at least one confirmation on both nodes, is likely simply just a propagation delay.
Answer: In 99% of cases, it's because a miner has mined a block that has propagated through to the website and it hasn't reached the client yet. In the other 1% of times, it's because there has been a block chain fork and there are two block chains that are valid. Both possibilities are temporary things (almost always) and will fix themselves when the next block gets mined or sooner.


Which state benefited the most from the Great Compromise? (US)

Question:
Under the terms of this compromise, in the first chamber of
  Congress—the House of Representatives—the representatives would be
  apportioned according to the population in each state. This, of
  course, was what delegates from the large states had sought. But in
  the second branch—the Senate—each state would have equal
  representation regardless of its size; this provision addressed the
  concerns of small states.

Which state benefited most from this? When I look this up, I only find answers saying that every state benefited. But I have to choose one that benefited the most. Which state benefited the most from the Great Compromise?
Comment: Define your use of benefit.
Comment: Yeah, we're not here to do your homework.
Comment: You seem to have your answer but i'll say this anyway. If this is homework as suggested it might be that you are required to express an opinion and justify, there might not be a right or wrong answer. If this is the case the question might not fit the format for stack exchange.
Comment: You must choose one for what? This seems like an opinion based question. Is this supposed to be backed by statistics?
Comment: @Braydon https://i.imgur.com/PIUPl8D.png That's my guess but I have no idea what the right answer is.
Comment: How am I supposed to find the right answer if it's supposedly an opinionated question?
Comment: It was multiple choice, there was a right answer, it was "Delaware".
Answer: It's always going to be somewhat of an opinion which state benefited the most, but we can try and constrain it.
First of all, we have to look at what the alternatives were.  Under the Virgina Plan, the biggest states would have had the most power.  Thus, the Compromise can be said to have benefited the smallest state the most - per the original apportionment, that was Delaware, which only got one representitive in the first House.  Under the New Jersey Plan, all states would have been equal in power, which would mean the smaller states would be relatively more powerful.  Thus the Compromise can be said to have benefited the largest state (Virginia) the most, by giving it the most overall power, especially compared to absolute equality.
Secondly, we have to look at the timeframe involved.  Both Delaware and Virginia could be said to have benefited the most when the Compromise was enacted.  But beforehand, under the Continental Congress, each state delegation got one vote, so Virginia gained the most relative power with the new Constitution.  Conversely, today Alaska, Delaware, Montana, North and South Dakota, Vermont and Wyoming could all be said to benefit the most from having equal representation in the Senate (since they only have one Representative), or California can be said to benefit the most (from having the largest House delegation).  I'm not going to do the math to figure out which state benefited the most overall over the entire length of US history, but that would also be a valid calculation to make.
Answer: I would say Wyoming benefits the most as it is the least populous state but one member of it's three member delegation has near equal power to one member of California's 55 member delegation.  The delegation in full will be elected by the same group of people (as will any state with a three member delegation), so they will usually be close in political thought.  This means, that in effect, all Wyoming will have a more monolithic power and will be able to vote on something with three times the representative power of per number of delegates of states with 4 or more members of the delegation more often.  This is true of other 3 delegate member states, but as they represent the same ~500,000.  Wyoming will effectively have the voting force of ~150,000 in all issues where the deligation is in agreement, giving them the most power for the least amount of citizens.  Meanwhile, where California's sentators will likely be a monolith representing nearly 80 million voting force combined, their House side is decidedly purple so that combined force can will in theory vote with a force of ~160 million, but will rarely reach that because it has significant opposition party votes, so the true force is much smaller.
This really doesn't matter in the legislature so much as the presidential.  Assume a situation where:

The election in each state is so close, that each candidate wins by one vote in the states they win
The winning candidate wins by the smallest possible margin of electoral college voters, such that they win enough to get to 270 and over by the last state to create the win.
Washington D.C. is included.

In a possible scenario where the victor candidate wins by taking only the largest possible states by population, and in every race he either wins by one vote or loses by one vote, then the candidate becomes the President with only 22% of the popular vote.
In a possible scenario where the victor candidate wins by taking only the smallest states possible by population, and in ever race he either wins by one vote or loses by one vote, then the candidate becomes the President with only 21% of the popular vote (the winner takes D.C.).
Therefor, because of the slight advantage in the Presidential races, and the more unified nature of the delegate votes, the compromise slightly favors small states in the extremes.  As Wyoming is the smallest state in both scenarios by population (including Washington D.C., which has no voting representation in congress and still is slightly more populous than Wyoming) it stands to reason that Wyoming has the most power per capita of any state, thus is the biggest beneficiary of the Great Compromise.
Comment: @PoloHoleSet:  Suffice to say, swing states are not about size of the state's population, but unreliability of a state to trend towards one political ideology.
Comment: The counter-argument would be that a state with a lot of representatives gets more Electoral College seats so they get pandered to by national-level politicians more in terms of attention and favorable policies. Low-seat-count states get ignored.  I don't have an opinion on which is right, myself, just offering another possible take on it.
Comment: @PoloHoleSet:  Not necessarily.  California has the most electoral votes and is never campaigned to in seriousness because it's reliably Democrat.  Texas is runner up with 38 and its reliably Republican.  Florida is pandered to (I should know, I used to be there... and registered independent) because the paty lines are reliably split such that the margines are less than one percent in any given year.  Beyond that, PA (20), Ohio(18), VA (13), NC (15) and NH(4).  Ohio is the most critical in recent elections as no Republican has won without it.
Comment: Very good point. Still.... a small electoral state, even competitive, is still mostly going to get ignored comparative to larger electoral states, and, certainly, the ones that are large, even if reliably blue or red still get over-sized attention during the clown-brigade show we call the primary season.


50Ohm Coax presents 50 Ohms of impedance on which frequency?

Question: Either there's a simple answer that I'm not finding in a spec sheet somewhere, or, I'm asking the wrong question!
Answer: For practical purposes, all frequencies.
If you cut a transmission line into infinitesimal segments, each segment can be modeled as:

simulate this circuit – Schematic created using CircuitLab
($G$ is conductance, the inverse of resistance)
The characteristic impedance is:
$$ Z_0 = \sqrt{ R + j\omega L \over G+j\omega C } $$
($\omega$ is the angular frequency, two pi times the ordinary frequency in hertz)
Wikipedia has the full derivation, if you're interested.
For a lossless transmission line, the resistance and conductance are zero. So the equation simplifies:
$$ \require{cancel} \begin{align}
Z_0 &= \sqrt{ 0+j\omega L \over 0+j\omega C } \\
&= \sqrt{ \cancel{j\omega} L \over \cancel{j\omega} C } \\
&= \sqrt{ L \over C }
\end{align} $$
and there is no longer any frequency term.
Real transmission lines of course have some loss, but if the transmission line is any good the loss will be low, and have negligible effect on the characteristic impedance.
Answer: The characteristic impedance of a line does change with frequency.
At high frequencies the loss components are effectively zero and $Z_0$ depends only on $L$ and $C$ (per unit length).
But at low frequencies, $R$ (and $G$) cannot be ignored and contribute significantly to the line impedance. There is a "corner frequency" where one regime takes over from the other.
Belden publishes a graph on their blog which I reproduce here:

The site PRC68 (Archived) has a detailed derivation of the equations, which I won't transcribe here, but the summary of the examples includes these surprising figures:

$600\Omega$ Open Wire Lines as seen on telephone poles, the corner frequency is 194 Hz.
CAT5 cable, with two AWG24 wires twisted together, has a nominal impedance at high frequencies of about $110\Omega$. Below 100 kHz though, its impedance rises to $750\angle{-46}^\circ \Omega$ (yes, a complex $Z_0$)
RG-58 has a corner frequency of 36 kHz, below this its impedance rises.

See also this excellent PDF by Audio Systems Group, which shows the impedance of a $75\Omega$ coaxial cable rising to $1000\Omega$ at 1 kHz, and almost $10k\Omega$ at 1 Hz.
None of this really matters for hams! You can see the impedance of the coaxial cable is stable down to 100 kHz. It matters (used to matter) to telephone companies, running many kilometres of cable, and carrying frequencies down to 300 Hz.
Upper frequency limit: At even higher frequencies, the coaxial cable starts to support higher order waveguide modes, when its impedance (and loss) changes dramatically. This occurs when the cable diameter is more than $\lambda/2$, approximately.
This effect could possibly be a problem for hams.
On cellular phone towers, before the radios were moved to the mast top, the long run of coax introduced a significant loss. Large diameter cables are used to keep this loss as small as possible, but the cable can't go bigger than about 2 1/4" because the cut-off frequency then gets below 2 GHz, where the cable is used.  High power VHF transmitters for example use much larger cable.
Answer: Ideally, the impedance is not dependent on frequency. Practical limitations should be stated in the specs.
Also note, that the effective impedance seen at the end of the coax is affected by power travelling "upstream", for example reflected/standing waves. These have to be taken into consideration when there is an impedance mismatch down the transfer line causing part of the power to be reflected back.
Comment: Hello and welcome to ham.stackexchange.com!
Comment: @rclocher3 TNX! I wonder why I haven't popped in earlier!
Answer: The impedance given in a coaxial cable data sheet is its "characteristic" impedance, not its actual impedance.  What that means is that "50 Ω" coax will have the least loss when the output impedance of the transmitter is 50 Ω with no reactance, and the impedance of the load (the antenna) is also 50 Ω with no reactance, irregardless of frequency.  In the real world the characteristic impedance does vary a little when the frequency changes, but those slight changes result in losses that are too small for hams to worry about.
For people who aren't electrical engineers, the behavior of transmission lines can be quite confusing at first.  RF circuits just behave very differently from DC circuits.  For instance, if you were to short the far end of a transmission line that is electrically a quarter-wavelength long and then measure its impedance at the near end, you would find a very high impedance, essentially an open circuit.  The ARRL Antenna Book does a good job of explaining the subject.
Comment: Would the downvoter care to explain, or suggest improvements?
Comment: RE:  _...What that means is that "50 Ω" coax will have the least loss when the output impedance of the transmitter is 50 Ω with no reactance ..._  Just to note that transmitters are designed to drive a certain load impedance (often 50 Ω), but their internal source impedance is much lower than that specified load impedance.  If it equaled the load impedance, then 50% of the output power generated by the final r-f amplifier in the transmitter would be dissipated as heat, within the transmitter.
Comment: @RichardFry thanks, I didn't know that!


How can I tell if my image is CMYK from Linux command line?

Question: I'm converting images from RGB to CMYK.  How can I tell if my image is CMYK from the Linux command line?
Answer: The simple way to get this info is by using identify command of the ImageMagick Package, try:
$ identify -format '%[colorspace]' image.jpg

Comment: 'Single' quotes _are_ needed. If omitted then a filename such as %c would be matched inadvertently.
Comment: The 'single' quotes are not needed and for me it worked better without them
Answer: identify is part of the ImageMagick toolset.
$ identify -verbose foo.jpg | grep Colorspace
  Colorspace: CMYK
$ identify -verbose foo.jpg
Image: foo.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Class: DirectClass
  Geometry: 3872x2592+0+0
  Resolution: 72x72
  Print size: 53.7778x36
  Units: PixelsPerInch
  Type: ColorSeparation
  Endianess: Undefined
  Colorspace: CMYK
  Depth: 8-bit
  Channel depth:
    cyan: 8-bit
    magenta: 8-bit
    yellow: 8-bit
    black: 8-bit
  Channel statistics:
    Cyan:
      min: 0 (0)
      max: 255 (1)
      mean: 65.169 (0.255565)
      standard deviation: 57.6369 (0.226027)
      kurtosis: 0.308901
      skewness: 1.17232
    Magenta:
      min: 0 (0)
      max: 255 (1)
      mean: 67.0774 (0.263049)
      standard deviation: 47.216 (0.185161)
      kurtosis: 1.37996
      skewness: 0.914289
    Yellow:
      min: 0 (0)
      max: 255 (1)
      mean: 117.456 (0.46061)
      standard deviation: 70.6394 (0.277017)
      kurtosis: -1.07218
      skewness: -0.180885
    Black:
      min: 0 (0)
      max: 239 (0.937255)
      mean: 40.826 (0.160102)
      standard deviation: 49.258 (0.193168)
      kurtosis: 1.56001
      skewness: 1.50352
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 58.1056 (0.227865)
      standard deviation: 63.7107 (0.249846)
      kurtosis: 0.0487218
      skewness: 1.03517
  Total ink density: 331%
  Rendering intent: Undefined
  Interlace: None
  Background color: white
  Border color: cmyk(223,223,223,0)
  Matte color: grey74
  Transparent color: black
  Compose: Over
  Page geometry: 3872x2592+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: JPEG
  Quality: 80
  Orientation: Undefined
  Properties:
    date:create: 2011-12-23T13:00:23+00:00
    date:modify: 2011-12-23T13:00:23+00:00
    jpeg:colorspace: 4
    jpeg:sampling-factor: 2x2,1x1,1x1,1x1
    signature: 972c47bd4a83e6561f2ddd65c2a5ca217ea06955814815bfb9d35ccd6b83fec2
  Profiles:
    Profile-icc: 1829040 bytes
      ISO Coated v2 (ECI)
  Artifacts:
    verbose: true
  Tainted: False
  Filesize: 3.968MB
  Number pixels: 10.04MB
  Pixels per second: 21.35MB
  User time: 0.460u
  Elapsed time: 0:01.469
  Version: ImageMagick 6.6.0-4 2010-10-20 Q16 http://www.imagemagick.org

Comment: +1 As this method gives new users an impression what other info might be queried with identify.
Answer: On Mac OS X, you can use
sips -g space <filename>

Example:
$ sips -g space file.jpg
/path/to/file.jpg
  space: RGB

Or, only printing the relevant information:
$ sips -g space file.jpg | tail -n1 | awk '{print $2}'
RGB

Comment: Thanks!  I'm on Ubuntu.  I dont see sips in the apt repository.
Comment: @EricJohnson Ubuntu is not a Unix. Mac OS X is, though. I'll keep this answer up, it might help others.
Comment: Just to preempt downvotes: **When I originally posted this answer, the question was very different and this answer was appropriate.**
Answer: I was able to do it with Perl's Image::Info library.  Here is the one liner I used on the command line:
perl -MImage::Info -E 'say Image::Info::image_info("foo.jpg")->{color_type};'

(Obviously this requires that you have the library installed already.  )


Cycles render blank

Question: I opened my Blender file and I saw that in Cycles rendering mode the scene is blank even though there are lights in the scene.
Answer: Looks like your Grass particle settings (40000 strands of grass!) are choking Cycles. I suggest you turn that down, and add interpolated children.
Comment: How to you add interpolated children?
Answer: To answer your comment with images...
Change that 40k number to something that your PC can handle, like 1000 or something

Then go down to Children
Click on Interpolated and add value 40 here:

I choose 40 because if you have Number set to 1000 and interpolated to 40, it basically means that every single 1 grass will be rendered as 40 strands of grass... (that means 1000 * 40 = 40000)... You can play with it better and even if you use something more complicated, you can use display amount 1 (that shows you how it looks in 3d viewport) and separate number for render amount that is only visible in renders...
When I tried to render it, it froze, so I went to very low numbers and set Number for Grass to 10... this is what your grass looks like in render:

There are these weird strands making circles... I didn't understand why is it like this but I found the problem here:

I don't know why you put value like 6 here, it make base of your hair extremely wide, making these weird circles, and that's why it couldn't render, it took too many resources to render...
So lower it down to default 0.01 and you will get something like this:

Now I add higher number to Number like 20 000:
Comment: I have tried doing that and it is still blank and the sample rate stays the same. https://imgur.com/a/Xy1bOo
Comment: Okay I just found where your problem is.. .I am sorry I didn't try to render it, it even froze my OC 5800X at full speed... the reason is quite simple and yet a bit weird because I don't know what you wanted to do with it... I edit my answer with new images

Cycles render blank


What is the army in Joel 2?

Question: I've always heard that the army described in Joel 2 was some kind of end-time army, but reading about in the NLT (as in the link) the chapter subtitle is "Locusts Invade like an Army". Is there a Biblical basis for either position?
Answer: There is very similar imagery in Revelation to particular verses in Joel. A comparison is shown below:

Joel 2:4-5 (NIV)
4 They have the appearance of horses;
they gallop along like cavalry.
5 With a noise like that of chariots
they leap over the mountaintops,
like a crackling fire consuming stubble,
like a mighty army drawn up for battle.
Revelation 9:7-8 (NIV)
7 The locusts looked like horses prepared for battle. On their heads they wore something like crowns of gold, and their faces resembled human faces. 8 Their hair was like women's hair, and their teeth were like lions' teeth. 9 They had breastplates like breastplates of iron, and the sound of their wings was like the thundering of many horses and chariots rushing into battle.

So, there is support for the idea that Joel's Army is an end-times army. But wait! Shortly after that bit in Joel, there's these few verses:

Joel 2:25-26 (NIV)
25 "I will repay you for the years the locusts have eaten—
the great locust and the young locust,
the other locusts and the locust swarm[b]—
my great army that I sent among you.
26 You will have plenty to eat, until you are full,
and you will praise the name of the LORD your God,
who has worked wonders for you;
never again will my people be shamed.

This sounds more literal, and as such, it makes it seem like the earlier passages may have been metaphors. However, immediately after that, it's back into end-timey talk:

Joel 2:28-32 (NIV)
28 "And afterward,
I will pour out my Spirit on all people.
Your sons and daughters will prophesy,
your old men will dream dreams,
your young men will see visions.
[...]

As it doesn't really make sense that Joel/God would insert a short literal passage in a chapter of symbolism, I'm going to say that Joel's Army appears to be an end-times army.
Comment: Wow, could we have posted any closer together?  Upvoted for the Revelation reference.
Comment: Except, in Acts 2 Peter says that "end-timey" stuff from the end of Joel 2 was happening then (when Jesus first sent them the Holy Spirit).
Comment: @a_hardin: [chuckle] I never saw a "new answers have loaded" thing. I'm guessing you didn't either? :P
Comment: Nope.  We were less than a minute apart.  :P
Comment: @a_hardin: LOL. [high-five] :D
Answer: Joel 1 tells of an invasion of locusts which eats everything.

Joel 1:4-7 NIV
  4 What the locust swarm has left
    the great locusts have eaten;
  what the great locusts have left
    the young locusts have eaten;
  what the young locusts have left
    other locusts[a] have eaten.
  5 Wake up, you drunkards, and weep!
    Wail, all you drinkers of wine;
  wail because of the new wine,
    for it has been snatched from your lips.
  6 A nation has invaded my land,
    a mighty army without number;
  it has the teeth of a lion,
    the fangs of a lioness.
  7 It has laid waste my vines
    and ruined my fig trees.
  It has stripped off their bark
    and thrown it away,
    leaving their branches white.

Joel 2 describes what the appearance of the locusts will be like.  They will block out the sun like clouds and making a loud noise like an army.  After they devour a field, it will be like it has been devoured by fire.

Joel 2:2-5 NIV
  2 a day of darkness and gloom,
    a day of clouds and blackness.
  Like dawn spreading across the mountains
    a large and mighty army comes,
  such as never was in ancient times
    nor ever will be in ages to come.

   3 Before them fire devours,
    behind them a flame blazes.
  Before them the land is like the garden of Eden,
    behind them, a desert waste—
    nothing escapes them.
  4 They have the appearance of horses;
    they gallop along like cavalry.
  5 With a noise like that of chariots
    they leap over the mountaintops,
  like a crackling fire consuming stubble,
    like a mighty army drawn up for battle.
Answer: Compare Joel ch 1 with Matthew ch 13 - and understand that what is taken away in both cases, is the Word of God.
Joel is an Old Testament book, but it tells us of the "new wine," being cut off, which I believe to mean the New Testament Gospel; and the one who steals away God's Word, is of course Satan, the Devil - God's opponent, and our opponent.
It is clear from Joel, that the effect of the locusts (which is believe are false prophets and teachers), is one of destruction, and leads to much fear, corruption, and loss, among what started out as the product, and fruit, of God's Word, the Gospel of Jesus Christ - the love of the great body (church) will grow cold - the falling away of the body of Christ.
It culminates in what could perhaps be described as the very worst of the 'locusts,' "a people come, great and strong" - (but NOT a righteous people), the "northern army." (which I believe could be North America - home to the 'Toronto Blessing' - a powerful deception, that is corrupting the true Church of God - that being the baptized Church - the Holy Spirit filled Church - God's temple here on Earth - clothed with Power from on High to be a witness to God - doing His Will. See Matthew 13 v 37 - 43. This Scripture also relates to the Northern Army being destroyed - Joel 2 v 16 - 32.
Joel 2 v 25, relates to 2 THESSALONIANS 2, and DEUTERONOMY 13. "He who endures to the end shall be saved."
Joel 2 v 20, can be related to Matthew 13 v 37 - 43, and also Jeremiah 25 v 29 - 38.
Satan masquerades as an angel of light - false Christian prophets, and false Christian teachers, operate within churches, where they can influence people, fleece, and mislead them, feeding from them as wolves in the sheepfold.
God permits Satan to 'test' us, but God still destroys Satan in the end -2 Thessalonians 2.
God can tempt no man, so Satan has to be allowed to, just as he did with Job, just as he will be permitted to after the thousand years when he was shut away.
'Joel's army' as it is referred to, God's army as Scripture refers to it, is NOT made up of God's people, but they will present themselves as being God's people.
Please relate Jeremiah 25 v 29 - 38, to being 'slain in the spirit.'
And please also relate people hopping around their churches with Revelation 16 v 13 - 14.
There is much more to the manifestations of the 'Toronto Blessing,' than we may know, every manifestation, has a negative connotation - howling - like wolves, roaring - Satan roams around like a lion, looking for someone to devour, (see Joel 1 v 5 - 7), even the laughter, is it just Satan laughing at us, as he laughs through us - the manifestations are simply temptations, and operate in the same way as any other temptation (tongues is a God given GIFT, but should never be taken as evidence of a continued love and obedience towards God, only our doctrine, behaviour, opinions, and beliefs are evidence of our love and obedience towards God, for they indicate which spirit/Spirit has got our attention - test the spirits - test the doctrine, behaviour, opinions, beliefs.)
Comment: David, welcome to C.SE. just a note for next time, you need two line breaks, or two trailing spaces to achieve a paragraph break in the SE markup. I have fixed it here, but you can see your output just below the text entry box next time. Again welcome and if you are new to SE check out our [FAQ]
Answer: Joel 2:28-32 is quoted by Peter in Acts 2:17-21.  He says in verse 16 "this is that which the prophet Joel spoke of".  So in other words, Joel 2:17-32 were being fulfilled in front of their very eyes at that moment.
Now notice Joel 2:28 says, "after this..."  So the events leading up to Joel 2:28 had to be fulfilled before Peter spoke in Acts 2.  The only way this could be is if the army were the Assyrians or Babylonians.  They are the only two Armies to invade Judah in this way before Acts 2.  Rome invaded and destroyed Jerusalem in 70A.D.
Assyria invaded Judah in 2 Kings 18:23 about 100 years after this prophecy but never took Jerusalem.  Babylon invaded and took Judah and Jerusalem captive about 200 years after this prophecy in 2 Kings 24 .
It is the key phrase in Joel 2:28 "after this" that sets a least a range of time in which it had to be fulfilled.
Comment: Welcome to Christianity.SE! And thanks for providing an answer. If you wish to get further oriented on this site, please take the [Site Tour](http://christianity.stackexchange.com/tour). And for tips and pointers on getting the most out of the site, you can brows some of the articles in the [Help Center](http://christianity.stackexchange.com/help).
Answer: How about this. The army of the book of Joel maybe talking about people that turn into something that  eats flesh of anything living.  Somekind of zombie. It says when they fall upon the sword they will not be wounded and their face is the face of blackness . They run to and fro and climb on the tops of houses and climb the walls and run every one on their way.   kind of funny how all the shows and movies these days are all about that sort of thing. It also talks about that they eat the flesh  that your enemy is in your own house and daughter will turn against mother and son turn against father. They leap from the tops of mountains and climb on the top of houses and enter like a theif in windows.
Comment: Welcome to Stack Exchange! The questioner is asking for a "Biblical basis." Could you point to specific verses in the chapter your interpretation is based on? Or verses from elsewhere in the Bible where similar imagery is used and the connection is clearer?
Answer: My interpretation of Joel 2 is an army possessed with demons. If you look at Joel 2:9 it says they come in at the windows. Jesus comes in at the door. Demons come in any way but the door. Snakes and scorpions are demons also. There are many types and shadows to know in Scripture. In Luke 11:11-13, Jesus explains that if you ask for something of God, why would he give you a demon. The context was the Pharisee's were accusing Jesus of casting out demons in the name of Beelzebub, but why would Beelzebub cast out his own seed.  Joel 2 speaks of the Last Days so IMO, locusts would be an inconvenience, but I think Joel is predicting a war on Israel by human enemies. This army however is controlled by the devil and will bring about the Salvation of Jerusalem by the 2nd coming of Christ. Israel has had many battles but not every one was a Biblical happening. You can be certain this army will appear and will attack because a prophet has seen it.
Comment: Welcome to Christianity.SE! And thanks for offering an answer. Before offering further answers, I would suggest taking the [Site Tour](http://christianity.stackexchange.com/tour) to get oriented to this site. Also, please see the article, [How we are different than other sites](http://meta.christianity.stackexchange.com/questions/1808/how-we-are-different-than-other-sites) for some points about what is and isn't on topic here. Meanwhile, I hope you'll also browse some of the questions and answers here!

What is the army in Joel 2?


Are device drivers state machines?

Question: I know that device drivers are attached to device controllers, which have their own registers and some local buffer storage. I'm wondering if I can think of device drivers as little state machines -- i.e. do they read and write to memory, or not?
Comment: Depends, probably?
Comment: if the memory is finite it can be regarded as a state machine. a simpler driver is better from a quality assurance pov, less likely to have defects & more possible to verify. however most drivers probably are too complex to be modelled as one...?
Answer: Many device drivers do read/write to memory.  For instance, consider a network device; it reads the packets to be sent from memory and writes the packets it receives to memory.  Or think of a hard disk driver; it does something analogous.   So, ultimately, it will depend on the driver.
That said, device drivers often do have a portion of their internal state that can be thought of a state machine.  For instance, the states could be something like UNINITIALIZED, ACTIVE, SUSPENDED, where it is initially in UNINITIALIZED state on boot; after it initializes the device registers, it could transition to ACTIVE state; on suspend, it might put the device into suspend mode and switch to the SUSPENDED state, and so on.  This only accounts for part of the behavior of the device driver, but it can still be a helpful way to organize the driver.  Or, in other words: often, some important aspects of the driver's behavior or state can be thought of as DFAs even though that's only approximately true.
Comment: Okay, so it seems like you're saying that drivers often can be thought of as DFAs even though that's only approximately true. Is that accurate?
Comment: @EliRose, yes, roughly, thank you for the concise re-statement.  Often, some parts of their behavior/state can be thought of DFAs (even though this might be only approximately true).
Comment: @EliRo I don't wish to answer, being too far outside my area of
competence. I think a lot of drivers, not just in computers, but also
in all types of equipments, including airplanes, are programmed with
synchronous parallelism techniques. My limited recollection is that
you have a finite state backbone, driving sequential code fragments.
This can be programmed with specialized parallel programming languages
such as Esterel, Lustre, and others. The compiling technology uses
finite state technique at its core, but goes much beyond that
mathematically. Maybe someone can develop better than I can.
Comment: @EliRose As memory comes back, vaguely, I think the finite state aspects
relates to the exchange of synchronicity signals, that can be
understood as the input tokens of finite state machines (sorry for
being very approximative).  Hence, D.W.'s answer would be consistent
with this idea of having DFAś at the core, with a little bit more
around it (the sequential code).
Answer: In software engineering, the "state machine" is more of a design tool than anything else. But yes, many device drivers are designed as state machines. This is because many hardware devices, or the protocols by which you speak to them, have distinct states.
Take the SCSI command protocol as an example. You can do SCSI over many devices (parallel, serial, USB, fibre, etc). However, the idea is the same: Send a command, wait for a response, send another command, wait for another response, and so on.
So we have two logical "states":

State 1: The driver is not waiting for a response from the device.
State 2: The driver is waiting for a response from the device.

There are also two kinds of "event":

Event 1: The operating system asks for some operation to be performed.
Event 2: The device sends a response.

In state 1, event 1 causes the driver to issue a command, and enter state 2. If event 2 happens, then something went wrong.
In state 2, event 1 might cause the driver to buffer the operation (say). Event 2 causes the driver to issue a response to the operating system, and then see if any operations are buffered. If so, issue a new command. If not, enter state 1.
This is a fairly simple device, and already we have something that looks pretty much like a state machine. Moreover, this device is fairly "smart", and doesn't require very much intelligence on the part of the driver. A dumber device, such as a floppy drive (which requires low-level commands like "raise the read/write head" and "move the read/write head 5 tracks that way") might require a lot of states simply because of all the moving parts that it's the responsibility of the driver to keep track of.
In general, a driver needs to keep track of the state of the device, and so state machines are often a very good way to design them.

Are device drivers state machines?


Bluetooth a pushbutton from one arduino to another to turn on a LED

Question: For a major project at school i need to get a bluetooth module to be able to communicate between two  HC-05 modules as a master and slave. They need to be able to press a pushbutton on the slave and it lights up a LED on the master.
I have been able to get the two hc-05's to connect to each other but i cant find a code and wiring that will work for what i need to do.
any help will be appreciated. Thanks
Comment: When you already have two arduinos and two hc-05 connected to each other, what wireup and code is missing?
Comment: please post the code that you have so far .... we can then give you some hints  .... please do not expect any ready made solutions, since this is a school assignment
Comment: The HC-05s are serial bluetooth modules. If you have connected the two HC-05 you already have send them AT commands via your serial interface. What is your problem with sending the needed information over the serial interface?
Comment: Do not post code as pictures. There is a function in the question editor to properly format code you inserted as text. Please use it
Answer: So, you have done the hard part and now need the easy bit :)
Firstly you need a button (failing that touching two wire together will just about do).  There are loads of quick tutorials on the web, here is one https://www.arduino.cc/en/Tutorial/Button.  They will end up with you having a pin that goes high or low when the button is pressed, you can either poll/loop to detect the press or go posh and use interrupts (leave that for later).  When the pin detects the press you need to send some data via your HC05 link to the master, something like 'ON' or 1, who cares so long as the master understands it.  And when it disconnects you need to send a off or 0 message (Remember the number 1 and the character '1' are not the same thing, so make sure you know what you are sending).
When the master receives the command it will execute a bit of code that will send a pin high (lets say pin 7).  Connected to pin 7 will be the +ve side of a LED, the -ve leg of the led will be connected to a resistor of 200-250 ohms and the other end of the resistor will be connected to ground.  Then when pin7 goes high it will light the resistor.

simulate this circuit – Schematic created using CircuitLab
As always you probably will need to break it down to test it, have a little app that toggles pin 7 high for 2 seconds and low for two seconds, etc (just like blink).
There is a phenomenon called 'bouncing' which is where the useless human finger presses a switch and doesn't instantly create a perfect connection and perfect disconnection.  This might make the slave send 101010101010101 when you just expect 1, you can either debounce using software or hardware, but only worry about that if you have a good quality switch :)


What's the difference between a dll and nuget package?

Question: First of all, I apologize if this is a basic question. I tried looking this up, but for some reason, I got more confused. So, I decided to ask here. Is a dll file and a nuget package the same? Are they both just being referenced in the project?
Answer: When you add features to your project via a nuget package, you're just adding files to your project.   It can be javascript files (like jQuery), DLLs that your project references (like Newtonsoft JSON),  or a whole bunch of things (like Entity Framework or Owin/SignalR) -- anything really.
The advantage of using the nuget package system is that it tracks it all for you.   It notifies you if your added packages received an update, it removes the files and unreferences them if you take the package off your project.    It handles all of that for you, so you don't have to track the files that the nuget package added, place them in special folders, make sure they get copied in your builds, all that micromanaging stuff.
Comment: niico - i use nuget packages whenever I can.   It makes it easy to remove packages (references) without worrying about cleaning up DLLs in a directory somewhere.   The VS integration lets me know when the nuget-references have updates to them.   I really prefer Nuget versus just dropping in a referenced file.
Comment: so is it ever better to use a reference to dlls than nuget packages when both are available?
Comment: a relevant note: MS have recently started referring to nuget as a "server side package manager" and are pushing bower & other client side package managers for client side libraries like JQuery (even though they are sometimes available via nuget).
Comment: Also in big projects consist of multiple softwares/applications in separated repositories , the required 3rd-party NuGet packages would be downloaded and installed automatically when a company member opens a solution of another team, and they don't need to track dependencies.
Answer: From the docs, https://www.nuget.org.

"What is NuGet? NuGet is the package manager for the Microsoft
  development platform including .NET. The NuGet client tools provide
  the ability to produce and consume packages. The NuGet Gallery is the
  central package repository used by all package authors and consumers."

A package can contain one or more dlls in addition to other assets such as config files etc.
Answer: You can add libraries via reference into your project but you would not notice when they were updated.
NuGet is a Visual Studio extension that makes it easy to pull in not only libraries but components, and most importantly their configuration into your visual studio project. It will help you manage your packages installed on your project and it will notify you when the package has new version released.
Let's say I created my own DLL, I could add my own DLL by reference. However, it won't be available in NuGet until I package and publish it first to make it available at the NuGet Package Gallery.


My new hamster is inactive

Question: My aunt got a new dwarf hamster for my cousin for Christmas. I have been keeping watch until Christmas morning and then I will surprise my cousin. I have put the hamster in its new enclosure, which is really small. My aunt did not know, so please do not be frustrated. The hamster has been very inactive and has been staying in place for most of the day. This is the second day of the hamster being here. Is it possibly sick, considering the lack of movement? He has been in his little tube, just sitting there sleeping.
Answer: It could be sick but not necessarily.
Hamsters are usually depressed once they are moved to a new enclosure. Smell is their primary sense so when they don't recognise the smell around them, they are upset. Once they are depressed, they get in their nest and stay there for very long periods.
Furthermore, you said it is a very small enclosure, which probably further pushed the poor creature into depression. EU requires the base area of the cages to be 0.12 square meters with a height of at least 30 cm. These are the minimum, not optimum values.
As a rule of thumb, when you move a hamster, carry some of the woodshavings from its old enclosure to the new one, to carry some familiar smell to the new cage.
Don't worry, depression is not permanent. Give him plenty of food and napkins/tissue papers to build his own nest. He will eventually get used to his new surroundings.
Make sure that your hamster is back to its proper enclosure and make sure that it is not too small.

My new hamster is inactive


How do you optimize an all equity portfolio while getting around the multicollinearity issue?

Question: I am trying to optimize a portfolio of domestic and international equity funds.  However being that they are very highly correlated it doesn't really help.  Is there a way to optimize and find an allocation which essentially provides the maximum diversification while minimizing risk? Could one translate these funds into factor and diversify across the factors then translate that back to weights for the portfolio?  Perhaps using PCR?
Comment: I have a suspicion that if you start with 100% allocation to a broad global portfolio like VT ( https://investor.vanguard.com/etf/profile/VT ) you already have a well diversified solution. You may want to see if adding any one other fund to the mix improves the situation. The "mean variance spanning test" of Huberman and Kandel 1987 offers a way to examine this question.
Answer: This is a matter of your preference aka utility function.  Perhaps the simplest reasonable approach would be the constrained Markowitz allocation
$$
w=argmax(w^T\mu - kw^T\Sigma w)\quad s.t.\quad w_i\ge 0,
$$
where $\mu$ is the vector of funds' performances, $\Sigma$ is their covariance, and $w$ is the vector of your allocations.  The weights will be inversely proportional to the risk aversion coefficient $k$.  To make this quadratic programming problem more stable, you may want to add a sufficiently generous constant to the $\Sigma$'s diagonal (ridge or Tikhonov regularization).  If the correlations are less than 1.0, you will get a modest improvement relative to an equal-weight allocation.  I expect a PCA regression will give a noisier allocation unless you regularize it somehow.


Will my hdd fail?

Question: I'm running badblocks in parallel on 2 identical hard drives. The problem is that /dev/sda has already finished without error the tests but /dev/sdb it at 363353920/488386583 (about 75%) but didn't report any error.
Is this a sign of hdd failure?
The tests are running from an emergency console and the server is dual E5520. Also the both HDD are from RAID1 array so the reads and writes were presumably identical.
Thanks for your answers.
Answer: The bad blocks you are getting may just be the return from the console not showing all the directive HDD space, because you are in RAID1 configuration the disk may take up some space which may return as bad blocks if you IDE/ATA array hardware is 3rd party such as a PCI card etc.
If so the bad blocks will be the console not reading the data through the card or the data only being able to display a certain disk space on your OS. This could well be the start of a disk error but i would put it down for ATA controllers before you go buying new drives. Your HDD may also become crammed with cache and cfg files for the RAID card.
Please advise on your hardware status.
Answer: It might be. Or might not.
It's possible your disk is failing, but it can automatically correct problems. Also, problems with cables, or controller (on disk side or on computer side) can cause that. Small number of bad blocks do not necessarily mean disk failure, even though then probability is higher.
It may also be that for some reason another disk was priorized higher (or another badblocks scan was priorized higher). If it's test ran by hardware controller, then it might not run both disks at the same speed.
If it's mission critical system, or if there is warranty service available, you should change disk anyway.

Will my hdd fail?


Absolute convergence of an infinite series and p-series test

Question: Why does the infinite series $\sum_{n=1}^{\infty}\frac{(-1)^n}{\sqrt n}z^n$ where $z\in \mathbb{C}$ converge absolutely for $|z|<1$. Doesn't the series diverge because if we apply the absolute values, we can use p-series test and since $p<1$, the series diverges?
Also, I am trying to find a value of $z$ with $|z|=1$ such that the series converges but I am stuck on this part too.
Comment: For $\lvert z\rvert < 1$, you have the domination by a convergent geometric series.
Answer: Hint

Use the ratio test to prove that the radius of convergence is $R=1$.
Use the Dirichlet's test to prove the convergence for $|z|=1$ and $z\ne1$, and for $z=1$ use the Leibniz criterion to prove the convergence.
Answer: No, that's only for ordinary series. You can see by the root test that
$$\lim_{n\to\infty}\left|\sqrt{n}z^n\right|^{1/n}=\lim_{n\to\infty}n^{1/2n}|z|=|z|$$
converges absolutely when this limit is $<1$, i.e. when $|z|<1$.
Answer: $$\sum_{n=1}^\infty\left|\frac{(-1)^nz^n}{\sqrt{n}}\right|=\sum_{n=1}^\infty\left|\frac{z^n}{\sqrt{n}}\right|\geq\sum_{n=1}^\infty\left|\frac{z^n}{n}\right|$$
If $|z|=1$, the rightmost part becomes the harmonic series:
$$\sum_{n=1}^\infty\frac{1}{n}=1+\frac{1}{2}+\frac{1}{3}+...$$ for which we know diverges. If $|z|=1$ diverges, $|z|>1$ should diverge as well. It follows that the LHS of the inequality diverges for these values as well.
Now, if $|z|<1$, the LHS of the inequality will become a sum of infinite geometric series with common ratio |z|<1 and converges.


What is a "mean earth orbit"?

Question: I have been researching about different satellite orbits online for a while now. I have read documents about low earth orbits (LEO), medium earth orbits (MEO), high elliptical orbits (HEO) and geostationary orbits (GEO). However, today I came across a new term: "Mean Earth Orbit", without google tell me exactly what it is. Does anybody know?
Answer: The answer lies in the classic theory of fields, and the unsolvablility of the many body problem.
In short, the langrangian for a planet in orbit contains many factors and there is more than one sphere of influence effecting it.
If there are three bodies interacting with one another, there will always be two systems that overwhelm the other.
What we get is a form of angular precession based on the perturbation of two gravitational fields, one field with an initial angular momentum of orbit and the other field with a perturbative thomas precession, as a result of a flux on the angular momentum.
$ L = mvr $, $ \dot{L} = \tau $
However $ \tau $ is constrained to a potential well between the three bodies, which causes the orbit to somewhat precess in it's own ellipse.
Another explanation of a mean obit, is the average apogee and perigee of the orbit, that's the regular farthest and closest distances respectively.

What is a "mean earth orbit"?


Limits for an user to make API Calls

Question: I know that we can make callouts based on Salesforce edition and its licenses, is there any limitations on user level ? i.e How many API requests can an user make in 24 hour period ?
Answer: The API limits are for Incoming calls, ie From 3rd party to SF.
There is no limit for outgoing callouts from SF to external system/endpoint except platform limitation of 100 callouts in 1 transaction and no callout after DML
Answer: API calls are metered per organization, not per user. Assuming a user has the Api Enabled permission, they can theoretically make as many API calls as the organization has available, subject to other limits, such as the concurrent request limit. In small orgs, this is pretty to do, while in really large orgs, a user might need to exceed 100 API calls per second to max out the org's limits.
Comment: @PranayJaiswal Admittedly, the question is confusing on second read--the subject suggests outbound from Salesforce, but the rest appears to be about inbound calls.
Comment: API enabled is for incoming calls not outgoing callouts?
Comment: @sfdcfox it's right. The question is about call in.
Comment: @sfdcfox  Can a platform user license with API enabled on the profile(user license: Salesforce Platform) will be able to make callouts. Need to build an integration with google maps and that will be used by the user with Platform license.
Comment: @user2815826 API Enabled does not affect callouts. A user wouldn't need this permission to make a callout. And yes, they should be able to make callouts just as any other user can.
Comment: @sfdcfox thanks!

Limits for an user to make API Calls


magento - nominal product show zero in subtotal shipping fee

Question: I have written a recurring payment module with asiapay payment,
however when i was in checkout progress, the shipping fee and subtotal is zero, although the actual fee will show up in the section below subtotal which is called "nominal item total",
it is still confusing for customer that the shipping fee is zero but it appears some value again in the last step.

Also , i am using table rate (price VS destintaion)....
at the step 3 SHipping method, it becomes worse that it did not find any shipping method...i am not allowed to move the step4!
So i would like to know how can i hardcode set the subtotal and shipping fee for nominal item checkout?
Answer: Shipping in: app/code/core/Mage/Sales/Model/Quote/Address/Total/Nominal/Shipping.php


any other button for e-level in viewfinder than DOF canon 1D x

Question: Hi all in the manual the only way to activate the e-level in viewfinder via the DOF button. Most of us use the DOF frequently. As this button seems to have only one function (no double task in connection with another button) this option is out for me as I need, or would use both equally often.
Is there any other option to activate electronic level in the viewfinder, maybe even via firmware??
Answer: You can also map the VF electronic level to either the M-Fn or M-Fn2 buttons in addition to using the DOF Preview button. Mapping DOF Preview to the M-Fn2 button is another option as well.
It's all on the chart on pages 336-37 of the original EOS 1D X Instruction Manual. (Note that the 1D X Manual for firmware version 1.1.0 places it on pages 340-341)


Workflow for a short animated film: what to do first, music or video?

Question: I really want to make an animated short film, but this is the first time and I don't know if I should make the music first or the film.
Answer: By short animated film I assume it is story driven and that there might be dialog.
The process is this:

write the script (with dialogue)
create storyboard, mood, concept art
record dialogue with video reference of that performance
select Temp music based on script and mood
animate based on script, storyboard, dialogue audio, temp music
compose real music and replace temp music, add sfx

In more detail you can read Pixar's Animation Process.

Why is it like this:
I will skip how script and storyboard is important, the question is not about these.
It is way way easier to animate facial and body expressions if you have dialogue and actor reference as source.
The final camera motion, animation and film cuts are also good sources for the music. However it is easier to cut footage to music than to cut sound to video. The reason is music has rhythm, which the footage might initially not correspond. Speeding/slowing footage and cutting it is easier than doing it with sound.
You solve this paradox by using Temp music, which is just some music already created, that you "steal" and use as reference to time your animations and to use as temporal guide for mood.
This temp music makes it a bit easier to get inspired for flow, mood and timing while animating (similar as with the dialogue audio). But it is no deal breaker if no temp tracks are used.
Making the actual music/score is the last step in creating animated short film.

On a side note:
It is by all means also possible to skip the Temp music part, and source all the flow and mood for animating directly from script and storyboard. The music is then inspired by the visuals (mood-board/story-board) and story emotions (animation/script) and is less restricted.
Temp music can be controversial, because your final score might sound like a knock-off. Because of this, it might be good to change the tempo or roughly re-mix the source for using as temp track.

More matter to watch:
Temp music from composer's point of view: video here
Temp music in film: video here
Comment: Well the film doesn't have any dialogue because i don't have any actors so music will fill in the dialogue or talking place
Answer: That entirely depends on what kind of short film you do.

If it's a music video or a film where the music is the primary element, then do the music first.
If it's story driven, then you build the story first and support the story with the music.

Unless you do something amazingly new, just ask yourself: Which part of your idea is the boss? If it seems like you will take a few decades to decide, either flip a coin or do both versions.
And in the end, if it's a small film and you fill all the positions yourself anyway, it can very well be that you work in both areas simultaneously. Because you start working on the movie after you have finished planning it. Which means script, storyboard and crappymatics and sound.
example: Last time in Clerkenwell


Tag creation request

Question: How to create a tag for a very new and specific topic, which have a really small number of followers (all of them with low reputation on stackoverflow) in the optic of having a growing community that help each others by answering questions related to the topic ( inexistant in stackoverflow for the moment ) ?
Comment: Tags are not created in the absence of questions. They are created when there is a sufficient number of questions about a topic. So have your users ask good questions. Then we'll happily add the tag. P.s. keep in mind that this is not your average support forum. We have quality guidelines for posts.
Comment: What's the tag?
Comment: You could ask your own question regarding the tool (which you can later answer yourself) and then request for a tag to be created for it. But depending on the tool, people may not be willing to create your tag
Comment: @musefan It's usually a matter of there being a couple of genuine, appropriate questions on the topic. And self-answered questions might be a way to get things started, but then the OP has to take really good care of asking both good questions and posting good answers. A good answer to a bad question will not save the post.
Comment: @Bart: Of course, all question and answers should be of the upmost highest quality... comments however, well no one gives a f*** about them!!!
Comment: [Right.....](http://i.imgur.com/smm4RYY.gif) @musefan.
Comment: I can't unfortunately as I have a low reputation.
I'm actually far from the 1500 required.
The tag I want to create is "lightning_workbench" It is a tool aiming at creating DSMLs based on Alloy. ( but It would be inappropriate to flood the Alloy tag with question related to this tool)
Answer: When someone with enough reputation asks a question about your tool they can create a tag to go with it. That's the way they get created. If a tag has no questions it will be removed by the system.
Comment: I got those points, but I was thinking that there was ,aybe an "hidden" way to create tag when they are actually needed.

Anyway, I guess the only solution is to find someone with the required reputation willing to create the tag ;) or to grow myself such a reputation but i guess it can take quite a long time X.x
Answer: Please see this post.  Tags get created when there's a clear need for them, not the other way around.
Comment: Hi and thanks for the answer, I already saw this post, but well, what if all of the person interested in the use of such a tag don't have enough reputation on stackoverflow ?

The tool is really specific , and only a short population at this very moment is interested in such a tag.
I intended to use stackoverflow as a way to grow a little community around the questions related to the tool.

But I guess it's not appropriate ...
Comment: @faboul that is appropriate use - others have done it (and others have tried and failed too).  the idea is the questions come first, then the tag.  Just have people ask a couple of questions and once there are enough (quality posts) someone will probably be happy to create the tag.
Comment: If it's a language you wrote, which was your original question, maybe you could have your own messageboard?  I use a popular 3rd party tool for C# development by a company called Infragistics, yet there's no Infragistics tag here.  So I go to their messageboard, where they have developers ready to answer questions.
Comment: I could indeed, I will need to think of this . anyway thanks for your useful feedback ;)
Comment: @JohnnyBones That statement appears to be false: [tag:infragistics]. There is probably also a tag for the specific tool that you use; I can't say because you didn't mention the name of it.
Comment: I'm sure there's no tag because I'm the creator of this tool. But anyway, thanks for your concern, I'll find another solution.

Tag creation request


Constructing explicit connected path for coefficients of monic polynomials with roots lying in the open left half plane?

Question: This is a bijection $\pi$ between $\mathbb C^n$ and the set of monic polynomials of degree $n$ defined by
\begin{align*}
\pi(\alpha_{n-1}, \alpha_{n-2}, \dots, \alpha_0) = t^n + \alpha_{n-1} t^{n-1} + \dots + \alpha_0.
\end{align*}
Let
\begin{align*}
  E = \{ \zeta \in \mathbb C^n: \text{All roots of }\pi(\zeta) \text{ have negative real parts}\}.
\end{align*}
By Vieta's formulas, we know $E$ is connected. Indeed, if we let $\Delta = \{z \in \mathbb C: \text{Re}(z) < 0\}$. Then $E$ is the image of $\underbrace{\Delta \times \Delta \times \dots \times \Delta}_{n \text{ times}}$ under a continuous function. I am wondering whether it is easy to construct some explicit path. That is, suppose we have $a = (a_{n-1}, \dots, a_0), b= (b_{n-1}, \dots, b_0) \in E$, can we construct a continuous path $\gamma: [0,1] \to E$ with $\gamma(0) = a$ and $\gamma(1)=b$ explicitly?
Comment: It is irritating to begin your question with "Suppose we have a monic polynomial ...". I suggest to do it like that: There is bijection $\pi$ between $\mathbb{C}^n$ and the set of monic polynomials of degree $n$ defined by $\pi(\alpha_{n-1},...,\alpha_0) = ...$. Then define $E = \{ \zeta \in \mathbb{C}^n \mid \text{All roots of } \pi(\zeta) \text{ have a negative real part} \}$. Can you make explicit which continuous function has image $E$?
Comment: @PaulFrost: Thanks for your editing suggestion. The function is elementary symmetric functions of the roots given by Vieta's formulas.
Answer: If $e_0, e_1, ... ,e_n$ denote the elementary symmetric polynomials in $n$ variables, we get a continuous map
$$\sigma : \mathbb{C}^n \to \mathbb{C}^n, \sigma(\zeta) = (-e_1(\zeta), e_2(\zeta),...,(-1)^n e_n(\zeta)) .$$
You may interpret $\sigma(\zeta)$ as the coefficients of a monic polynomial $p_\zeta(z)$ of degree $n$ having as roots the components $z_i$ of $\zeta =(z_1,\ldots,z_n)$, where a root of multiplicity $k$ oocurs $k$-times in this sequence. In fact, $p_\zeta(z) = \pi(\sigma(\zeta)) = \prod_{i=1}^n(z-z_i)$ where $\pi$ was introduced in the question.
We have $E = \sigma(\Delta^n)$. This means that the set $E$ could alternatively be defined without reference to monic polynomials and their roots. Let $s : \Delta^n \to E$ denote the restriction.
Now it depends on what you understand by "explicitly construct some path from $a$ to $b$". You find $a', b' \in \Delta^n$ such that $s(a') = a, s(b') = b$.  Define $u : [0,1] \to \Delta^n, u(t) = (1-t)a' + tb'$. This is a path connecting $a'$ and $b'$, therefore $s \circ u$ is a path connecting $a$ and $b$. However, it is not obvious how to find $a',b'$. There is no general method to express $a',b'$ as a function of $a,b$ and in that sense $a',b'$ cannot be made explicit (if you could, you would have a solution formula for polynomials of arbitrary degree $n$ which in fact only exists for $n \le 4$).
Let us finally consider the map $\sigma$. For each $\eta \in \mathbb{C}^n$ the inverse image $\sigma^{-1}(\eta)$ consists of all $\zeta = (z_1,....z_n)$ such that the $\{ z_1,....z_n \}$ is the set of all roots of $\pi(\eta)$. Hence $\sigma$ is surjective. Moreover, the symmetric group $S_n$ of $n$ elements operates by permutation of coordinates on $\mathbb{C}^n$; the fibres  $\sigma^{-1}(\eta)$ agree with the orbits of this operation. Therefore $\sigma$ induces a bijection $\sigma': \mathbb{C}^n/S_n \to \mathbb{C}^n$.
We show that $\sigma$ is a closed map. It is known that $\max\{1, \lvert a_{n-1} \rvert, ... , \lvert a_0 \rvert \} = \lVert(1,a_{n-1},\ldots,a_0) \rVert_\infty$ is an upper bound for the abolute values of the roots of $z^n + a_{n-1}z^{n+-1} + ... + a_1z + a_0$ (Cauchy's bound). This implies that $\sigma^{-1}(B)$ is bounded if $B \subset \mathbb C^n$ is bounded. Now let $A \subset \mathbb{C}^n$ be closed and $(\eta_m)$ be a sequence in $\sigma(A)$ converging to some $\eta \in \mathbb{C}^n$. Then $Y = \{ \eta_m \mid m \in \mathbb{N} \}$ is bounded, hence $Z = \sigma^{-1}(Y)$ is bounded. Choose $\zeta_m \in A$ such that $\sigma(\zeta_m) = \eta_n$. Since $\zeta_m \in Z$, we see that $(\zeta_m)$ is a bounded sequence and has a convergent subsequence with limit $\zeta$. Since $A$ is closed, $\zeta \in A$. By continuity of $\sigma$ we conclude $\eta \in \sigma(A)$.
This implies that $\sigma$ is an identification map. Therefore, if we give $\mathbb{C}^n/S_n$ the quotient topology induced by the canonical quotient function $\mathbb{C}^n \to \mathbb{C}^n/S_n$, we see that $\sigma'$ is a homeomorphism.