What kind of spider is this please? Southern Indiana. Very strong web

Question:
It never comes out during the day so it's been hard to get a decent picture. We have been battling over ownership of my mailbox. It's a house box and every morning it's covered in cobweb from it to the siding or across the top of it if the lid was left up. Very strong web, it takes effort to get it off. I was going to put up a new one with a sealed lid but would kind of like to know if it's poisonous before I go messing about the battle grounds.
Answer: Even with lightening your photo:

It is difficult to ID this to genus. If you are only interested in knowing whether it is a medically significant spider, you can rest assured that it is not. The (few) markings and shape of it are enough to rule out widows and recluses.
From its shape and habitus, it is likely a cobweb weaver of some kind (family Theridiidae), but there are many possible choices for genus unless you can get a clearer photo. While black widows are also Theridiidae, the medically-significant female widows have solid black legs while we can see leg banding in this specimen. As @anongoodnurse points out in the comments, the legs here are shorter than a black widow's legs, so I would even rule out a male widow. The abdomen here is rounder shape than the tear-drop abdomen with a tapered end that a widow has. (Similarly, recluses do not have banded legs and do not hang in webs like this Araneoid is. And there are no other medically significant spiders you need to worry about in your geographic area).
The leg banding, general shape, and the slight white marking on the abdomen we can see in the lightened photo make this a little reminiscent of Enoplognatha marmorata (like this one https://bugguide.net/node/view/646186/bgimage). It is very rare to find Enoplognatha indoors.
Here is an example of an E. marmorata found in Indiana: https://www.inaturalist.org/observations/107343897
Comment: @anongoodnurse thanks - added additional info with my best hypothesis of a feasible ID.
Comment: It would be helpful if you could explain how/why you know it's not a widow-type spider, and even better if you could actually identify the spider. I'm not an arachnophobe by any means, but I would approach this one with some caution, as it's habitus is similar (though the legs don't appear to be as long.) Good answers on this site are backed by sources. Thanks!
Answer: The globular abdomen, posture in the web and general shape certainly suggest a Theridiid.  The glossy black body and banded legs are consistent with both the pretty harmless Steatoda species of "False Widows"and their more problematic cousins the Black Widows.  In both cases, the abdominal stripes and leg bands fade to black as the female matures, and while it would be unusual, I bet that having an all-black abdomen and still have traces of the brown banding on the legs is not too uncommon. However, Latrodectus mactans, which I think is the more likely Black Widow species in Indiana, would be expected to still show some of the red spots on the abdomen at this point in its growth. So I'm leaning toward a Steatoda.  Both are noted for strong webs, with the real Widows having a particularly strong silk; the simple ID solution is to check the underside - a real Widow will have the classic red "hourglass" marking, while a Steatoda will not.
The image below is Steatoda grossa, the bigger of the common "False Widows".  Steatoda borealis females commonly feature a white midline on the back, but I'm not sure if the photograph shows a real feature or just an artifact of the flash.


Is it possible to add a Legend to Temporal animation in QGIS

Question: I have a Temporal animation that shows the movement of tracked squirrels in the forest, there is a  different colour for each animal.  If I add a legend showing colours to the map it doesn't show in the animation.  I have got around this so far by using the Title Decoration but can only have an entry as "1323 = Yellow".  I would be better to show the colour.  I would apreciate any ideas how to acheive this.
Answer: A legend can be added by using Decoration-Image.  Write legend in Gimp with appropriate colours, make background transparent and export as png.  Then import with Decoration-Image and place where required.


Is the replacement $i\omega_n\rightarrow \omega+i\eta$ in Matsubara Green function valid?

Question: In many-body theory we know that to find the retarded Green function in frequency space $G^R(\omega)$ we first find the Matsubara time-ordered Green function $\mathcal{G}(i\omega_n)$ and then replace $i\omega_n$ with $\omega+i\eta$.
First question: is this operation well-defined? Since, for example, if I multipy $\mathcal{G}$ by $1=e^{i\beta \omega_n}$ (for the bosonic case) the replacement $i\omega_n\rightarrow \omega+i\eta$ does not give the same answer as before. I know that both of these functions are related to the Hilbert transform of the spectral weight as
$$G(z)=\int_{-\infty}^{\infty} \frac{dx}{2\pi}\frac{\rho(x)}{x-z} $$
and that makes sense to me because in that case we have a function of real variable $z$ and the replacement (analytic continuation) $z\rightarrow i\omega_n$ gives a unique answer. However the reverse operation doesn't seem to give a unique answer.
Second question: is this replacement an actual analytic continuation?
Answer: In order to go from the Matsubara Green function to the retarded one using analytical continuation, you need to express the Matsubara Green function as a sum of simple pole terms. This is what results from the Lehmann representation.


"Type Error occurred when creating object: Magento\\Eav\\Model\\Entity\\Attribute\\Source\\Config"

Question:
I have migrated from ver 1.9 to 2.3
Answer: Try to look at the customer eav attribute with select value for frontend_input column in eav_attribute table, make sure the source_model column value is not null or empty or it fills with correct class. You can set value for frontend_input column to int if you wanna work on the source_model later
Comment: saved my day, thanks
Comment: I love the suggestion of changing the `frontend_input` to `int` for debugging purposes.  I have a custom M1 attribute that came to M2 with `source_model` set to `NULL`.  Changed the `frontend_input` from `select` to `int` and the page works.  Now I know the source of the bug and can determine how I want to migrate that data / fix it.
Comment: Yes, it work, replace select with int or add source_model for these attributes
Answer: Go to the table eav_attribute and search for attribute "mailchimp_store_view" and deleted this row after taking backup of your table. it will fix your problem. i was also facing same issue. it worked like a charm. give it a try.
Answer: As noted by most, this seems to involve attributes that did not cleanly migrate / has migration data issues
In my case it was an customer address attribute called 'address_valid'
A sure fire way to debug this is to just debug with a breakpoint in PHPSTorm on Magento\Eav\Model\Entity\Attribute\Source constructor

make a small temp edit to function definition

and step through until you hit the null one(s).
You can also go with a conditional (mine happen to the be first attribute calling that routine, so I had nothing to step through)

Look back in the trace log until you find the AbstratAttribute.php entry, and select.

Then check within the class data for the offending attribute data
Answer: Please run this three commands and check:
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento cache:flush

Answer: After a long debug and review migrated database I found the reason

During migration I found that some of custom attributes were not there in migrated DB ( I don't know, Why !).
Another important point is we should check the options for the select
type attributes( options had not been migrated in my case).

These 2 can be the possible reasons for the error.
Answer: I was experiencing the same issue when trying to edit customers accounts and after checking the 'eav_attribute table' using Idham Choudry's answer here, i checked the table against a working Magento (2.3.4) and found that MailChimp had an erroneous attribute which had migrated over from Magento 1.9 but is now no longer needed.
After taking a backup of the database I simply deleted the 'mailchimp_store_view' attribute from the eav_attribute table and I can now edit customers again.
Finally i re-installed Mailchimp and everything is now working perfectly again.
Hope this helps anyone with the same problem
Answer: I had this same issue. It turned out to be some extra entries (not columns or source model) in the "eav_customer_attribute" table. Once I removed these entries the page loaded and worked fine.
I also found that this issue caused the customers address to be saved as a new entry on every order.
Answer: In my case it was a plug-in attribute.
In \www\vendor\magento\module-customer\Model\AttributeMetadataResolver.php
around line 116 there is the public function getAttributesMeta.
Here add a bit of debug code to find the problematic attribute:
var_dump($attribute->getAttributeCode());

Refresh the page. You should see some attribute codes printed in top of the page before the error. Its the last one that gets printed before the error. In my case it was allowed_payment_methods.
Remove the attribute from the eav_attribute table and you should be good to go.

“Type Error occurred when creating object: Magento\\Eav\\Model\\Entity\\Attribute\\Source\\Config”


Is it possible/advisable to upgrade a DD-WRT router remotely?

Question: I have two DD-WRT routers in different locations.  One of them is running the VPN version of the firmware, and the other is running the standard version.  I am on location with the VPN one, and I want to upgrade the other one to run the VPN firmware so I can wire them together.  Is this possible or advisable?  Of course, I don't want to lose the settings on the remote one, since then I would lose my remote access (currently through SSH) and not be able to configure it.
Answer: I can't rule out the possibility of doing it but I can make some points against it.

The recommended process (strongly reiterated by DD-WRT) involves a series of 'hard' resets that involve power cycling while holding down the physical reset button on the router. Tricky to do remotely :)
Saved settings for one version of the firmware should NEVER be used with a different version.
Answer: It's never advisable to upgrade any router remotely, unless you have separate out-of-band access to it.
I base that recommendation on a decade of running the core networks for an ISP (in a previous job)
Answer: I can say from personal experience that I have nearly bricked my router trying to upgrade DD-WRT over the web interface via remote connections. I would strongly recommend being physically connected to the router and having physical access.
The hard reset procedure that is officially recommended also comes in handy if anything goes wrong.


How to answer to 精一杯頑張ってきます?

Question: I was talking with my japanese penpal and he wrote to me 精一杯頑張ってきますよ! after I wrote him おはようございます!お仕事頑張ってきてね! because he told me he was going to work. I don't know if there's an answer or not. In English of course I would not  respond as there's no answer to "I'll do my best". But as we are talking in Japanese and not English, I would like to know if there's a way to respond or not.
Comment: How about just a 気を付けて? Or, since it's already mid-afternoon, and he probably won't check his phone/PC, お疲れ様? If he rather works too hard, maybe a 頑張りすぎないでね?
Comment: I would leave that without an answer tbh, especially because that already is an answer to your 「お仕事頑張ってきてね」.
Answer: Usually I'd say it depends on the person's way of speaking, but here I feel like any reply would be "too much". At best, you can reply with a smiling face and keep it simple.
Other than that, if you really want to talk to him/her, you can change the topic, even though after this kind of conversation where there's not really much going on, it might feel like you're trying too hard to talk to him/her, and it'd end up being weird.
Or you can try to make a "joke" like "Lend me some motivation haha" and hopefully (s)he will reply with a more creative message...
But to be honest I feel like this kind of things is common to every language.
Edit: Now since some time has passed maybe you could send お疲れ様です as suggested (assuming (s)he has finished work) but that's not really part of the question since it'd be a completely different conversation

How to answer to 精一杯頑張ってきます?


Only Site Collect Admin can deploy SharePoint?

Question: I am trying to deploy a SharePoint 2010 project onto an SP server. When I hit F5 after building the solution, the output says that "Only a site collection administrator can activate or upgrade solutions that contain code." Does this mean I have to deploy this on the site collection admin's server account, or can impersonating that admin in web.config suffice?
Answer: You can choose Run as different user in Visual Studio and give a site collection admin's credentials when starting Visual Studio. Else you can add the current user as a site collection admin and proceed further.
Answer: If the solution contains an assembly, only a site collection administrator can deploy it. If the solution does not contain an assembly, a user who has the Full Control permission level at the root of the site collection can deploy it.
http://technet.microsoft.com/en-us/library/ee721992(v=office.14).aspx
Now Fix to this problem. Add the account into Site collection admin or run the Visual Studio under that account.
How to add the user.Log on the site collection with admin rights and do this
<code>Site Actions->Site Permissions->Click on 'Site Collection Administrators' under 'Edit' tab
</code>
Add the id through which you have created sandbox solution.Now deploy your sandbox solution right clicking on solution again.Finally sandbox solution gets deployed into the site
Comment: This is a good point. I did not know the assembly thing.


Making two sequential asynchronous requests using promises

Question: The following code is making two asynchronous requests to obtain the desired data. The second request needs to access the data from the first request, hence I need to nest it. I know that it is better to chain promises, but this is a case where nesting seems necessary.
However the lint raises a warning: avoid nesting promises. Should I ignore the warning or there is a better way to rewrite the code?
function get_note_full(note_id) {
  return db.collection('notes').doc(note_id).get()
    .then(doc => {
      const data = doc.data();
      return get_author_data(data.author_uid)
        .then(author => {
          return ({
              id: note_id,
              title: data.title,
              text: data.text,
              author: author
            });
        });
    });
}

Answer: You should be able to convert that code to using async / await from ES2017. Notice that I changed the function names to suit general JavaScript naming standards (camelCase for functions and variables, etc.)
async function getFullNote(noteId) {
    const note = await db.collection('notes').doc(note_id).get();
    const author = await getAuthorData(note.author_uid);
    return {
        id: note_id,
        title: data.title,
        ext: data.text,
        author: author
    }
}

This is how MDN defines an async function:
An asynchronous function is a function which operates asynchronously via the event loop, using an implicit Promise to return its result. But the syntax and structure of your code using async functions is much more like using standard synchronous functions.

Link: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function


Is it possible to generate a transaction request that populates all tx fields, except signature?

Question: Does Ethereum have the basic functionality to allow a payment request to be generated which the user can then choose to accept and sign?  The application for this is a token auction where the payer's assent to the contract is included in the memo field.  Therefore, I wish to be able to pre-populate the memo field in a payment request.
Answer: Definitely. The transaction can be created in entirety and the user then is given the prompt to sign using their private key (there are various methods for them to do this and is represented by the tx.sign(privatekey) in the code below).
Pre-populating the memo field is possible as well since all data is encoded in the data portion of the transaction.
If your question is rather whether the user's signature can be included in the txn/contract data then that is a different story, although possible, not as straightforward as having the user sign a transaction.
<code>var rawTx = {
    nonce: web3.toHex(nonce),
    gasPrice: web3.toHex(web3.eth.gasPrice),
    gasLimit: web3.toHex(gaslimit),
    from: web3.toHex(fromAddress),
    data: web3.toHex(contractData)
};

var tx = new Tx(rawTx);
tx.sign(privateKey);
var serializedTx = tx.serialize();

return web3.eth.sendRawTransaction("0x" + serializedTx.toString('hex'), callback());
</code>
Source


How Come the Doctor Doesn't Need A Blast Suit?

Question: In Journey to the Center Of The TARDIS, the TARDIS crashes in the ship of Gregor, Bram and Tricky. After the Doctor convinces the three to enter the TARDIS, they don gas masks and blast suits. The Doctor also puts on a gas mask, but omits the blast suit. My friend told me it was because "He's the Doctor," but I never took this to heart. Why didn't the Doctor put on a blast suit? Was it somehow because of his Time Lord biology?
Comment: He doesn't need a suit! He's already a blast!
Comment: He's not human. He has the ability to survive in vacuum (for some time) and breathe some poisons. It's just part of who the character is.
Comment: It's kind of a wibbly-wobbly thing.
Comment: Answer: He's The Doctor. Just accept it.
Comment: /me wiggles fingers
Answer: Time Lords in general are highly resistant to things normal humans are, like for instance radiation.
An example of this is different forms of radiation such as Rontgen in the episode Smith and Jones he talks about how he used to play with bricks of them in the nursery.
Not to mention that overall Gallifreyans in general are very resilient to a number of different things like the cold as seen in the episode The Tomb of the Cybermen.
Also when they went into the Tardis there was just a lot of smoke and gas that was leaking so it was funneled out by The Doctor using fans. Further into the episode the only real danger that is posed is from the Eye of Harmony which creates the creatures seen in the episode explained by the Doctor when he states that The TARDIS was trying to save it's passengers and inadvertently causing their cells to burn creating the said creatures.
One last thing to mention is that we don't know how much the blast suits protect their users anyway.  The humans had no idea what was waiting inside of them in The TARDIS so they went as prepared as they thought they would need.  The Doctor himself knew better, if the amount of radiation or dangers were lethal even to him he would have worn some sort of suit as well. And given that The TARDIS was in fact rather somewhat intact on the inside besides the gas and fumes leak it can be seen that there wasn't any more form of danger as far as radiation or the like.
Comment: I take your point about Time Lord resilience to otherwise fatal phenomena and his possible foreknowledge of what he would encounter in the Tardis but we know the Doctor is somewhat vulnerable to radiation from Tennant's death in 'The End of Time'.
Comment: That is mainly because he funneled all the radiation into that one concentrated area.  There are scenes where he absorbs radiation and is fine, like the one with Martha where he shakes it into his shoe.


Trap light in a cage

Question: Is it possible to build a mirror cage in order to catch light in it?
Let's assume the surface of the mirror reflects absolutely 100% of the light.
Which shape of cage is the best to do this?
Is it also possible to "fill" up the cage with light?
Comment: This doesn't really appear to be about worldbuilding, and as such is likely to be closed, Might suggest this is better suited for physics.SE, they'd be able to give you much more detailed explanation. but on the face of it, i'd suggest this could be possible, but whatever aperture was sued to introduce the light into the box would eventually allow the light to leave it, i don't think any shape would be so much better than another at stopping this
Comment: I agree.  Not only is this a 100% physics question as written, but you're asking about the corner cases.  Physics.SE will be a better place for that.  Worth noting is that the sub-optimal version of this shows up all over the place in physics.  LIGO's main mirrors could potentially reflect a photon 3.3 million times (on average), and the whole setup is designed to bounce about 280 times before going into the detector.  These are truly practical questions.  The extreme limits, with perfect reflectors, will cross into the land of QM.  You're far more likely to get a good QM answer on Physics.SE.
Comment: I know that it's impossible to do so with our current understanding of physics. that's why I wanted to ask it here with the science fiction tag. In my understanding, light is a form of energy. What if it is possible to trap light in an object to build a weapon for example. thta's the purpose of my question.
Comment: I've made a theoretical super villain who can control illumination and reflection. In other words, he can make a mirror box that glow and reflect light at the same time. As others have stated, it would be impossible with real physics, and without magic to allow light to enter, but not to leave. It would also have to be a perfect vacuum to be feasible to trap light perfectly.
Comment: Hi, I did a slight edit on your question to make it more readable.  I removed the [science-fiction] tag because nothing in your question points to it (even if your intent is to use it for scifi).  I added [light].  I do not see anything in your question that relates to [macroengineering].  Are you implying that you want an extremely large cage?  If so, you should add that to the question.  If not, you should remove that tag.
Comment: I will second Blade Wraith's suggestion to migrate to Physics SE. You will likely get better answers for this question over there than over here... and I would really like to see the physics behind this truly unusual scenario!
Comment: See https://what-if.xkcd.com/35/ for what happens when you continue emitting power inside a perfectly sealed enclosure.
Comment: There are a lot of people saying that getting light in means letting light out and that that causes issues for trapping significant amounts of energy. If you're already hand waving things you might like to hand wave a substance which essentially radiates light until it is completely spent - I.e. over a certain amount of time all of the matter is converted into light. Basically "frozen light" in a "similar" sense to dry ice. "Dry light"?
Answer: It may stretch the parameters of your question but I believe a combination of slowing the speed of light and capturing it in a lossless optical fibre system could do this.

The speed of light is normally about 186,000 miles per second, or fast
  enough to go around the world seven times in the wink of eye.
Scientists succeeded in slowing it down to 38 mph.
They did this by shooting a laser through extremely cold sodium atoms,
  which worked like "optical molasses" to slow the light down.
https://abcnews.go.com/Technology/story?id=99111&page=1

By transforming the optical fiber span into an ultralong cavity laser,
  we experimentally demonstrate quasilossless transmission over long (up
  to 75 km) distances and virtually zero signal power variation over
  shorter (up to 20 km) spans, opening the way for the practical
  implementation of integrable nonlinear systems in optical fiber.
  https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.96.023902

The device could consist of an incredibly long coil of optical fibre rolled into a ball and placed into your cage. Light would be fed into one end of the fibre-optic cable until it was 'full'. It would then emerge from the other end over a period of hours.
If the light was to be kept for longer, the end of the cable could be connected back to the input. The light would go around the circuit until required.
Comment: Well, OP has clearly not defined how big, noisy and energy-hungry this cage is allowed to be. I imaginge any device capable of cooling an incredibly long coil of optical fibre to the required temperatures and keeping it there for any practical amount of time would be huge and rather not transportable.
Comment: The storage part could be done at base. Once the circuit was complete, it wouldn't matter if light were to speed up. Then you just have to transport the cage.
Comment: @zovits that's a question for the OP, but energy use definitely won't rule this out.  The LHC cools the wires that power the magnets along its entire loop (17 miles) down to < 2K so that the wires powering it can be superconducting.  If that is possible, then this is possible.  For reference the LHC uses about 200MW, while a modern nuclear reactor on US naval vessels might generate up to 500MW of power.  Of course a large chunk of that energy goes into colliding things, not just cooling things.
Answer: 100% reflective mirrors do not exist in reality. The best we can get is dielectric mirrors, with reflectivity around 99.9% at specific wavelengths.
That aside, if you want to trap light, just shape the mirror as a sphere with perfectly reflective surfaces. Any photon inside the sphere will keep bouncing in the sphere.
A similar concept is employed in the making of the integrating sphere (the only difference being that it is not perfectly reflective)

An integrating sphere (also known as an Ulbricht sphere) is an optical component consisting of a hollow spherical cavity with its interior covered with a diffuse white reflective coating, with small holes for entrance and exit ports. Its relevant property is a uniform scattering or diffusing effect. Light rays incident on any point on the inner surface are, by multiple scattering reflections, distributed equally to all other points. The effects of the original direction of light are minimized. An integrating sphere may be thought of as a diffuser which preserves power but destroys spatial information. It is typically used with some light source and a detector for optical power measurement. A similar device is the focusing or Coblentz sphere, which differs in that it has a mirror-like (specular) inner surface rather than a diffuse inner surface.

I have not been able to find any reference to the cited Coblentz sphere, though.
Comment: I think the holes in the sphere kinda defeat the purpose of trapping the light.
Answer: Not with conventional mirrors: Even with something like 99.9999999...% reflection, there are losses. The light is reflected back-and-forth a trillion times inside a box, which causes the seemingly insignificant loss to accumulate fast enough and the light fades almost instantly, in human perception.
Edit: Based on SpoonMeiser's comment, the optic fiber has a bulge somewhere along the fiber. The light is trapped and spirals back-and-forth along the bulge. The length of the bulge determines the frequency of the light it can trap. The article has no mention how light is caught and then released on command.
A resonance bottle is a very small molecular structure
Comment: That last sentence feels like an incomplete thought; I think this answer would be improved by expanding on it.
Answer: No, because light moves at the speed of light. That means it can cover the circumference of Eart multiple times in a second. You will let all the light out before you can close the lid.
Also each photon will impart momentum to the walls upon hitting them, even if they are magically 100% reflective. Over finite time they will lose energy and become non-visible radiation.
You can get more kick for your money by buying a battery and a flashlight.
Comment: 100%reflective necessarily means the photon loses no energy. It will impart momentum to the wall, sure, but the wall will impart an equal and opposite momentum to the particle. Closing the lid might cause some mechanical challenges unless the box is really big though.
Comment: @Renan sure. it's possible to build that machine with a lot of handwave. But my idea builds on the technology of carbon nanotubes. This material, also known as the "blackiest" black color on earth, is able to trap 99,99% of the light in it, by absorbing their energy. I want to do exactly the same, but without absorbing the energy but preserve it.
Comment: @D3f4u1t "Absorbing" energy means the photon is lost and its energy is converted into thermal energy, i.e. heat, which then starts to dissipate and radiate away, but can be considered as "preserved" for a while. So using black paint you can transform light into heat, and using a thermal engine you can transform a part of this heat back into usable energy again (e.g. into mechanical movement, which is used to generate electricity and then use that to power a lightbulb). The catch is the required complexity and the unavoidable losses at each step.
Comment: The speed of light is only relevant when you want to catch a particular photon. When you place the box inside the sunlight with the upper lid open, it will quickly reach the point where the incoming amount of photons is the same as the amount of outgoing. Then, closing the lid is a no-brainer.
Comment: "Also each photon will impart momentum to the walls upon hitting them" - Nope. Since this is a rigid box, any momentum imparted to one wall will cause the opposite wall to gain the same velocity, which will add energy to the next photon which hits the opposite wall.
Comment: so it could be possible if the scale of the cage is bigger than, let's say 300 million m/s ?
Comment: @JoeBloggs I believe 100% reflectiveness implies  o photon absortion, but does not imply lossless collisions.
Comment: @D3f4u1t if you can magic up a machine that big that won't collapse, you can abracadabra anything.
Comment: The speed of light is not constant - it's constant *for a given medium and refractive index*. See chasly's answer above for an illustration of this. Arguing that something happens too quickly is like saying we'll never be able to travel to the moon because escape velocity is a whopping 11km/s.
Answer: Q1: Is it possible to build a mirror cage in order to catch light in it?
Yes in fact there is an existing term for this in physics and engineering: The Optical Cavity
https://en.wikipedia.org/wiki/Optical_cavity

An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. hey are also used in optical parametric oscillators and some  interferometers. Light confined in the cavity reflects multiple times producing standing waves for certain resonance frequencies.

(emphasis mine)
Non-physicist explanation
Optical cavities are literally a pair of mirrors or other material that reflects light. They are configured so that a light wave reflecting on either mirror will keep the same frequency and overlap strongly with the other light waves in the cavity. When this happens the totality of light waves in the cavity will 'constructively interfere' and add up thereby forming a single more powerful light wave of the same frequency. As you pump more light waves into the cavity, by keeping the same frequency on each reflection, you may continue to add up more light waves thereby forming an extremely energetic light wave. This behavior is called resonance. Consequently, when you remove one of the mirrors after doing this for some time, the cavity will emit the powerful resonant light wave. The light wave emitted will carry the total energy of all light put into the cavity but as a single wave (boom laser).
Errata:
* Photons and Light Waves are the same thing (per wave-particle duality). I call them light waves here to drive home the wave mechanics that make this work.
* When the constructive interference occurs, the two waves are essentially adding together. Since mirrors are not perfect, or their placement might not per perfect, said interference will not be perfect either. Consequently that means the waveform after interference will carry sub frequencies or nodal pairs. This will change the overall resonance behavior or may cause issues with the cavity as a whole (heating it up or light escaping)
* Resonance is occurring because multiple waves will constructively interfere over time forming a more powerful photon or set of photons. Since interference is not perfect, ultimately you can get close to resonance but not perfect. Ideally the cavity should be adjusted or automatically adjusted to keep as close to resonance as powerful and to emit the wave before the cavity fails or becomes permanently damaged.
Q2 Which shape of cage is the best to do this?
According to the stability diagram for a two mirror cavity, the most stable configurations are plane-parallel and concentric (upper right and bottom left of the linked diagram).
Q3 Is it also possible to "fill" up the cage with light?
Yes. See above.
Comment: A perfect cavity is impossible, and since you can decompose any standing wave into travelling ones, even standing waves will decay rapidly without added input to maintain the state.
Comment: With the right materials it's certainty possible ---especially within the realm of world building. For instance DOI: 10.1103/PhysRevB.88.165116 developed a meta material with 99.999% reflectivity and less than 0.001% absorptivity  for short-wave 1.5 μm infrared light
Comment: You need a lot more 9s to be useful there. Assume a basic scenario of a beam bouncing between mirrors. How many bounces does it take to lose 95% of the beam? 0.95 = x^n, so n ln x = ln 0.95, n = ln 0.95/ln x. For x = 99.999%, that is 5,130 bounces. If your box was 2m long, then your beam will cover 5,130 * 2 m = 10, 260 m, which will take about 0.000034s = 34 us. So if you close the box instantaneously, you have 34 us to point your 2m box at something, and have 5% of what you put in. Suppose we want to contain it for 1 s? We would need x=99.99999997%, again to get just 5% of the input back.
Comment: 1. OP's questions never asked about effectiveness, efficiency, or implementation, simply if it was possible.
2. I never claimed a perfect cavity was possible. You're criticizing minutiae the OP never inquired about.
3. I've updated the answer to directly answer OP's 3 questions.
Answer: Without assuming an extremely (and unreasonably) fast means of replacing the entry aperture with a (perfect) mirror, or and extremely (and unreasonably) large cage, even if you grant perfect mirrors it won't work.
Regardless of mirror geometry, the fact that any beam of light will spread ensures that eventually all of the light will bouncing around with essentially uniform dispersion, and some of that will hit the entry aperture and exit the cage. This process will automatically self-regulate, so that the power exiting the aperture will equal the input power.
For "reasonable" cage sizes, as you close the aperture the input power must drop to zero, so the exit power must drop to zero as well, and the energy content of the cage must drop to zero.
The obvious way around this is to make the cage very big. Then the speed of light will allow you to close the aperture fast enough to allow some light to remain within the cage.
Comment: Your third paragraph is wrong: if input power is zero and exit power is zero, the energy content of the cage *must remain constant*.
Answer: If you have a mirror that can reflect 100% of the photons that land on it, it doesn't matter what shape you use. As long as the container the light is placed into is perfectly sealed and the inside is a vacuum, you will be able to store it in the cage forever.
Why? because your material is 100% (not 99.9999%, 100%) reflective, it will absorb no energy and shoot out as many photos as it receives with the same velocity. Light is never absorbed so just keeps bouncing around. The shape only matters if you want to store more energy, because you will need to increase the length the light bounces before it exits the box. I would recommend a very long and straight box, shoot the light in almost parallel (the closer to parallel the better) to the entrance and let it bounce all the way down and out. Seal the Box and you have the light trapped inside.
Now you need a vacuum. If there is anything else inside except a vacuum you will lose energy. Why? because your photos are going to hit the molecules inside the box and be absorbed by it in the form of heat energy. So even if the outside is perfectly insulated and reflects 100% of the energy, eventually all your photos will have hit that one special molecule that is still inside the box and you will just have one super fast molecule bouncing around inside.
Finally you can't exactly fill up a shape with light. Light has no mass and doesn't take up space. It can interfere with itself, but thats about it.
Answer: If you don't need mirrors you could convert (compress?) light into matter for easier storage and then back again when needed.

Trap light in a cage


about sigma delta filter bit-width

Question: I am working on a Sigma Delta ADC project, and need to decide the bit-width of the digital filter.
My filter has 4 stages, the first is CIC and the bit width is 29 bits according to the OSR. My final filter output is only 24 bits. So this means the other 3 FIR filters need to reduce 5 bits in total. If my input is 4-bits signed and output is 24 bits signed, OSR=256, how to decide the bit reducation of each the 3 filters. What's the impact of the performance due to the bit-width reduce. Any comments?
Answer: I think your problem might be a bit too domain-specific for StackOverflow.  I do code-based DSP myself, and I have only the dimmest understanding of what you're asking.  KVR Audio has an excellent forum where you might be able to get some help with this problem.

about sigma delta filter bit-width


What could cause my old gas furnace to keep cutting out?

Question: I have a old gas furnace that keeps cutting out. It turns on and the when it hits the temp it turns off and then when it turns on it will not give it gas. It will just sound like it blowing but no air comes out of the vents. And I can't see any flame in the furnace. I have had an repair guy come out and all he did was hit the little reset switch in the furnace and it fixed it. For a little while at lest, now I have to do it at lest once a day. I don't know what is wrong. I don't what to keep calling someone out to just hit the reset switch. Dose anyone know what is wrong?
Answer: I would check your ignition sensor or your flame sensor. There are also heat switches that "melt" and shut off to stop the furnace from catching fire. I had a similar problem when I bought my house that was a foreclosure. The furnace sat for a while and the sensor got covered in dust and burnt out when I turned the heat on. The best way to figure out what's up is to remove the cover and look for some blinking lights. It will depend on the furnace type. These lights will give you a code that will help you figure out what the real problem is. So
Google your furnace model and how to find the code
then
Google your furnace model and the code to get an idea of the problem
Comment: +1, clean the flame sensor with some fine grit sand paper. On some models the exhaust blower will run continuously while nothing else is happening; this can indicate a failed safety switch.


BPMN: multiple roles in a row

Question: How do I model a process which can start by either Role1 OR Role2 performing the first task? I would not like to use "Role1 or Role2" in the lane description
Answer: The BPMN specification does explicitly not specify the exact purpose of lanes (p. 304/335 in PDF).
Consequently, the approach Role1 or Role2 is actually compliant with the specification. The approach is also not far away from good practice. Adding multiple roles and even individual users as candidates to a task is often possible when configuring processes in BPX (Business Process eXecution) systems.
Typically, you would create a new role that encapsulates both Role1 and Role2 - let's call it Role1;2. This makes sense from an information systems perspective. For example, if you execute the process with IT support, you need to grant Role1 and Role2 access to the system/component that allows executing your first task. When configuring the access rights, the administrator will create a new user group - Role1;2 that contains the the user groups Role1 and Role2.
Note that a process role doesn't necessarily map to a job title. For example, a person who is employed as a Software engineer might share the process role Specification writer with a System analyst.
Comment: Then, the same concept applies, which means you have to create separate lanes. In the example I mentioned: The role _specification writer_ is an own lane, containing the task _write user story_. Because the role _specification writer_ is applicable to both _software engineers_ and _system analysts_, either of them can take the task. The following task - _implement feature_, for example - is then in the _software engineer_ lane, because it can be handled by this role only.
Comment: Thank you. So there is no way to handle this in the two existing lanes of software engineer and system analyst at all? The model is complicated already and I would prefer not to create a separate lane for just one tasks that is performed by the roles which already exist in the model.
Comment: Thanks Timotheus. What if not all tasks in a lane are performed by these two roles? Example: 2 roles in the process, both of them can complete the first task but as soon as the first task is completed, the roles for the following tasks are clearly defined

BPMN: multiple roles in a row


how to get erc-1155 totalSupply

Question: I want to know how many tokenIDs are in an ERC1155 token, how can this be achieved?
I want to know how many tokens are in a specific tokenID, how can this be achieved?
Are there functions in the specifications that allow for that?
Many thanks
Answer: You could query the events TransferSingle and TransferBatch and make your calculation for how many tokens are minted. This applies also for your second question. But you always have to look at every implementation separately.

how to get erc-1155 totalSupply


How do you know if an insignificant P value is because of chance error or because the sample size of the data is too small?

Question: I have always thought that an insignificant P value is the product of chance causing variation in the data. However when I was watching a talk on a study, the presenter mentioned how the insignificant P value meant that the sample size of the data was too small to make any conclusions rather the being the product of chance error. How can you tell if an insignificant P value is caused chance error or small sample size then?
Comment: Why does there have to be a chance *error* rather than chance *variation* as you mentioned above?
Comment: Limiting cases are often instructive to think out even if they seem absurd. Thus suppose you're testing for normality. One data point and two data points are consistent with any normal distribution. Three data points give a tiny bit of extra  information about skewness or symmetry and four points give a bit more about tails of a distribution compared with the middle. Now the question of how many data points are enough is hard to answer well, because it is fuzzy, but the message that very small samples just don't carry enough -- or even any! -- information about the hypothesis is stark enough.
Comment: [Not entirely unrelated](https://stats.stackexchange.com/a/108914/44269)
Comment: @Alexis: [Significantly related](https://xkcd.com/882).
Comment: Wouldn't chance error increase with small sample size? So by chalking it up to sample size you are already including chance error?
Comment: Some significance tests have inference conditions to check. A common one about sample size is the large counts condition to check if there is enough data so that the sampling distribution of the data matches the distribution used to calculate the p-value. Right? For chance error of the conclusion of a test being incorrect, check the significance level to see if it is too high making a higher chance of a type I error.
Answer: The question basically asks what the truth is behind the observed p-value. But if we knew the truth we wouldn't need to compute a p-value in the first place!
I leave technical considerations regarding power to the other answers, but here's a bit about significance test logic.
The idea is that there is an underlying data generating process that we cannot observe directly, therefore we can't say what it truly is. We only see the data.
The p-value is a measure computed from the data that measures compatibility of the data with the null hypothesis. (I think that you use the term "chance" to refer to the null hypothesis, which often but not always interprets as something like "only random variation is going on".)
An insignificant p-value means that if the null hypothesis is in fact true, the data look pretty much as they should be expected to look like (regarding the specific test statistic at least; they may look different in other respects). They are compatible with the null hypothesis, they don't deliver evidence against it.
It does not mean that the null hypothesis is true, however. Data generating processes deviating from the null hypothesis may also produce data that look like this. Note also that most statisticians would agree with Box's famous quote that "all models are wrong but some are useful", so actually at best the null hypothesis may be a very good model (i.e. idealised mathematical description) for what's really going on, but never literally true.
The role of the sample size now is this: The larger the sample size, the more information in the data, and the better we can use the data to actually distinguish the null hypothesis from alternative models. If you have a low sample size, the data may not only be compatible with the null hypothesis, but also with models that are really quite different (and in a real context would have a very different interpretation). This means that a large p-value doesn't allow to say that we are at least close to the null hypothesis (meaning "chance variation" in some circumstances). If indeed an alternative model is true, larger sample size will make it more likely to observe a significant p-value (that is called "power" of the test). This implies that with a larger sample size, observing an insignificant p-value, we have some evidence that we're at least close to the null hypothesis.
However, note that if in fact the sample size is very small, we cannot tell these apart, i.e. you cannot say whether the p-value is as it is because we're in fact very close to the null hypothesis, or whether it is only because our sample size is too small and in fact an alternative model is appropriate that with a larger sample size would lead to significance. You can only know this collecting a larger sample! Post hoc power calculations do not address this question! What they tell you is, if you want, the degree of distinctiveness of the sample you have, i.e., how far away from the null you may have been without being able to find it. This doesn't mean that this is indeed the case, as in fact your small sample doesn't allow you to distinguish these cases!
Unfortunately there is a catch in significance test logic, which is that if you collect a very large sample, you will quite likely find a significant p-value even if the truth is, though slightly different from the null hypothesis, so close to it that regarding its meaning in the real situation you'd say that it is not in any relevant manner different from the null hypothesis (like, a true parameter may be 0.02 rather than 0, but you'd think that only parameters larger than 0.5 are worth bothering; obviously this depends on the exact situation, meaning of the data etc.). So indeed large samples may lead to significance often even when this is actually meaningless, which means that you always need to look at estimated effect sizes and possibly confidence intervals to say something more relevant than just whether something is "significant".
Comment: Great answer! Regarding the p-value and the estimated effect, it is good discipline to consider the importance of the effect size. Cox emphasizes that statistical inference is an element of scientific inference. One approach is to use a format like "is statistically significant but economically insignificant" or "is clinically and statistically significant", etc, depending on the particular subject area.
Answer: Ideally, you would have run a 'power and sample size' procedure
before doing your experiment. Then you you will have known all
along whether you had a good chance of rejecting $H_0$ if an effect of
the desired size leads to rejection.
Of course, when you are working at the 5% level of significance, there is by definition a 5% probability of rejecting a true null hypothesis. So you can never really be absolutely sure you reach
a correct decision.
If you did not do a power and sample size procedure at the design
phase of experimentation, then doing an ad hoc power analysis
is probably better than just wondering. But you need to understand
that an ad hoc power determination cannot be exactly the
same thing as one done at the proper time. Power analyses at the
design phase almost always involve making some guesses, and you
will likely have to make fewer guesses ad hoc---or at least think so.
Perhaps the main reason for avoiding ad hoc power
analyses arises when you fail to reject when you think you are
'entitled' to a rejection. This can tempt some people into
"P-hacking" procedures such as 'suddenly realizing' that you
really intended a one-sided test all along, or dredging through
the data with unwarranted ad hoc tests looking for 'something like'
the 'unfairly withheld' rejection. At any stage of the experimental
procedure, a power analysis is not a guarantee. It is a prudent precaution. If you could figure out whether to reject via a power
analysis, you wouldn't have to do the experiment.
If no effect is found, many of the experimenters (and thier bosses) may be disappointed and intent on finding the reason for no rejection. Somebody (often the project statistician) has to have the guts to say, the real reason no effect was found may be that no effect exists.
Comment: What exactly do you mean by an *ad hoc* power analysis? Calculating post hoc/observed power based on the observed effect (which is basically just a transformation of the respective p-value), or ignoring the observed effect and calculating power based on the effect size that would have been expected before collecting the data, or adjusting your beliefs about the true effect size based on knowledge before collecting the data and information from the data analysis and calculating power based on this adjusted effect size, or something different?
Answer:
The presenter mentioned how the insignificant P value meant that the sample size of the data was too small

This is very wrong.

The p-value does not indicate whether the sample size was too small.

It is the estimate of the error/deviation in the measured effects that indicates this.
(Along with a relative comparison of the size of that error and the size of the suspected effect that one hoped to be able to measure. The error should be smaller than the effect that you hope to measure.)

What this presenter is saying is presumptive. An insignificant p-value can occur when the sample is too small. But... it can also occur because there is no effect. It sounds like this presenter presupposes the presence of an effect and bases the story of the discussion and conclusion around this
It is also a bit silly to state this as a conclusion. It is a bit like saying 'the experiment failed' while hiding that it already failed before it started because the sample is too small (instead it looks like the presentation makes the 'too small sample' is a discovery). In order to know that the sample is too small you do not need to observe an insignificant p-value. You can already determine beforehand whether a sample is going to be too small to be able to detect a certain magnitude of effect. The only situation when this is not the case is when there is no reasonable a priori estimate of the variance that might be expected on the measurements. But even then, one should not say that the insignificant p-value means that the sample is too small.
Comment: It is like we use only the following two options ***1** If the p-value is low: reject the null hypothesis **2** If the p-value is large: consider the sample size too low to be able to reject the null hypothesis.* This appears to me as conclusions with a point of view that already supposes that the null hypothesis is false. Why do the research in the first place? To me this feels as being against the idea of p-values. They are not meant to lead to this ditochomy. Neyman and also Fisher didn't mean it to be like this.
Comment: (+1) In the social sciences in particular, it's actually a defensible proposition, a point Paul Meehl made in the 1960s, cf. https://www.jstor.org/stable/186099 You're completely right that you should consider power beforehand of course but in my experience many people with a background in the social or biological science will happily interpret a non-significant result from an underpowered experiment as evidence of equivalence and completely ignore the possibility that the sample size was too small. Maybe this presenter was trying to emphasize this?
Comment: @Gala I agree that my comment/answer might be considered harsh towards the presenter given that the background is not clear. It could be that the presenter wanted to address multiple options. Still the sentence *"the insignificant P value meant that the sample size of the data was too small"*, which I believe is the spark behind the question, just sounds wrong to me.
Comment: Meehl was indeed strongly against the (over)use of p-values. We profess to believe the null hypothesis could be true but often it is very contrived and not really plausible. If it can be presupposed to be false then we urgently need to frame our research differently. A bunch of people have made similar arguments more recently (Andrew Gelman type M and type S errors for example).
Answer: You do a post hoc / a posteriori power analysis. It answers the question: how likely was I going to find an effect given the size of my sample and the observed effect size (roughly speaking). There is a WIDE range of methods to calculate this given your statistical methods. If you find that you had very little chance of finding an effect with your sample size given the data, your sample size may have been too small.
There are plenty of resources on this:
Differences and relation between retrospective power analysis and a posteriori power analysis?
Also look at G* Power, it's a piece of software often used for this.
Comment: Doing such a search may turn up articles such as [Post Hoc Power Calculations are Not Useful](https://data.library.virginia.edu/post-hoc-power-calculations-are-not-useful/)
Comment: None in particular. But there will be loads. This is a very common topic from beginner to pro.
Comment: Are there any good youtube videos you would recommend that explain this well. Sorry I am just somewhat of a beginner with statistics
Comment: I assume just search for posteriori power analysis?
Answer: There are two main types of error: Type I error, where we reject the null hypothesis despite it being true, and Type II error, where we fail to reject the null hypothesis even though it is false. The probability of getting a Type I error, conditioned on the null hypothesis being true is called $\alpha$, and $1-\alpha$ is the sensitivity of the test. The probability of getting a Type II error, conditioned on the null hypothesis being false, is called $\beta$, and $1-\beta$ is the specificity or power of the test. Methods to estimate $\beta$ are called "power analysis".
$\alpha$ can be calculated from the null hypothesis; one of the requirements for a proper null hypothesis is that it is precisely stated enough that $\alpha$ is known. Calculating $\beta$, however, requires a precise alternative hypothesis; an alternative hypothesis that consists of merely saying that the null is false is not enough. For instance, if the null hypothesis is $\mu =0$, then we would get different $\beta$ for an alternative hypothesis of $\mu = 1$ versus an alternative hypothesis of $\mu = 2$.
How much a parameter differs from the null hypothesis is the effect size (this is often further qualified as "true effect" to distinguish it from "observed effect", with the former being the difference in the actual parameter, while the latter is the difference in the statistic measured from the sample). The main factors affecting power are sample size and effect size. The larger these factors are, the higher the power. For a small sample sizes, a failure to reject the null can be caused the small sample size, the null being true, or chance. But as the sample gets larger, the probability of failure to reject being due to chance gets smaller and smaller, and it becomes easier to draw conclusions.
Since the actual effect size is unknown, we can't know for certain what the power is. But we can, given bound on the effect size, give bounds on the power. For instance, if a drug killing one in a million people who take it is an acceptable risk, we can ask "Given an effect size of one in a million, what's the probability that a drug trial would find no statistical significant difference in fatality rates of those who took the drug?"
Answer: The long answers are mostly correct, but only address your specific question indirectly. The short and direct answer is that you can gather evidence that will help you decide if your sample size is too small or if your data are misleading (due to error or due to natural sampling variation) ONLY by gathering another sample of data.
The reasons that you need another set of data can be had from the longer answers.


My PS3 controller won't reconnect after plugging the cable back in

Question: When my PS3 controller is connected with the cable it remains connected, but when I remove the cable it disconnects and won't connect again.
Does anyone know what the problem is?
Answer: Problem solving if you are connecting the ps3 controller to a ps3 console.
This could mean two possible problems:
One is that your controller has a malfunction with its Bluetooth chip (which is also the microprocessor). Another is your console has a malfunction with its Bluetooth chip.
To see which one is try to connect a different controller to the console, if it works then is the first problem if not its the second, its usually the second problem.
The problem solving if you are connecting the ps3 controller to a pc are the same, except that your motherboard may not be able to make a Bluetooth connection. Check if it can.
Solution to this problem
Easiest solution is to buy a new ps3 console or controller depending on the problem.
Hard solution is to fix it by your own hand and hard work which means opening the ps3 console or controller and change the necessary components to fix the issue.
I have a couple of video if you want to see how to to the Hard solution.

Video of how to disassemble a ps3

Video of the possible Bluetooth chip solution (you don't have to do with cables but if you are capable do it)

Video of how to disassemble the ps3 controller

Link for the ps3 controller specifics and schematics


User's name in Ubuntu MATE 16.04 Panel

Question: I am new to MATE, and I've noticed some differences from Ubuntu 14.04/GNOME. For example, the Panel. I want to see what I am logged in as. There is no name in the top right corner any more, and in Users & Groups I see no option to display it. Can I set it elsewhere?
Answer: You can go to Control Center > About me
Or you could begin logging out, and a windows will appear saying

You are currently logged in as your name
Comment: That way I thought of myself. One can also look in Caja and look for the first entry, many ways to find out. But I want to see it, as I change user all the time at this stage of installation

User's name in Ubuntu MATE 16.04 Panel


Can you graph $y^{4}x^{3}+x^{4}-y=0$ without a computer?

Question: I'm trying to get an intuitive sense of algebraic varieties from their equations. Some varieties are more easily imagined without a computer since either $y$ or $x$ can be isolated, producing functions, and these can be more easily graphed. But what about for varieties like $y^{4}x^{3}+x^{4}-y=0$? Is there any way to think of its shape without a computer? One approach would be to use the quartic formulas to isolate $y$, but this is time consuming. Are there better approaches, if not to obtain a perfect graph, at least to obtain an estimation?
Comment: I have had a  good scientific calculator for some thirty years. It is programmable; once a function is defined, there is a "solve" function that finds a root between bounds I supply. The outcome is that I have always been able to draw curves in the plane.  I claim that getting graph paper and pencil and plotting points on a curve leads to some understanding of it.  You could try that.  Well, the real part of the curve...
Comment: One can always generate a "slope field" by taking derivatives on both sides and then begin plotting slopes. Another approach that works well is decomposing the equation into parametric equations but that is an art and not an exact science. It takes a lot of intuition or trial and error to figure out what works.
Comment: Sometimes [hyperbolic coordinates](https://en.wikipedia.org/wiki/Hyperbolic_coordinates) are useful for this.
Answer: One of the most effective way I know is to get a parametric equation of the curve by intersecting it with a line having a variable slope $y-y_0=t(x-x_0)$ passing through a point $(x_0,y_0)$ of the curve. Here we can take plainly point $(x_0,y_0)=(0,0)$.
The abscissas of the points of intersection of the curve with the line having equation $y=tx$ verify the following equation :
$$t^4x^7+x^4-tx=0$$
factorizing $x$ and considering that $x \ne 0$ (the case $x=0$ corresponds to the "trivial" intersection situated at the origin), we get :
$$t^4x^6+x^3-t=0$$
which is a quadratic relationship in $X=x^3$, with parameter $t$ whose solution(s) will give a (double) expression $x=f(t)$.
(see Edit below)
Finaly, the two equations $x=f(t), y= t f(t)$ constitute a rather natural parametrization of the curve.
Edit :

Details about function $f$. One finds, by solving the quadratic :

$$x=f(t)=\frac{1}{t}\sqrt[3]{\frac{-1 \pm \sqrt{1+4t^5}}{2 t}}\tag{1}$$
(for $t\ne 0$) (1) is valid under the condition that the square root makes sense, i.e., $t \ge t_{lim}:=-\tfrac{1}{\sqrt[5]{4}}.$
One finds, of course, similarities with the results obtained by Fabio Caiazzo ; however, using polar coordinates has a drawback : it doesn't give good results when the curve doesn't pass through the origin.

Especialy interesting results can be obtained if the curve has a double point (i.e., is self-interesting) by taking this double point as point $(x_0,y_0)$. This is the case for example with the folium of Descartes (see here).

Have a look at the curve : the red part corresponds with the case of sign "+" in (1), the blue part to sign "-". The limit case as been placed into evidence by showing the associated secant $y=t_{lim} x$ (the grey straight line) which is in fact a tangent.
This limit case separates the cases $t > t_{lim}$ whith two intersection points from the cases $t < t_{lim}$ where there are no intersection points.

Now, for infinite branches, as Somos has done, we can neglect one term after the other (this is authorized by the "technique" of Newton polygon) giving the following very satisfying approximations at the origin (maybe the most important) and when either $x$ or $y$ tend to $\infty$ :
Comment: For asymptotes and so-called "parabolic branches", see the techniques connected to [Newton polygons](https://en.wikipedia.org/wiki/Newton_polygon).
Answer: You can convert it in polar equation:
$$x=r\cos(\theta)\qquad y=r\sin(\theta)$$
So you have
$$r^{4}\sin\left(\theta\right)^{4}r^{3}\cos\left(\theta\right)^{3}+r^{4}\cos\left(\theta\right)^{4}-r\sin\left(\theta\right)=0\\
r^{6}\sin\left(\theta\right)^{4}\cos\left(\theta\right)^{3}+r^{3}\cos\left(\theta\right)^{4}-\sin\left(\theta\right)=0\\
r^3:=R\\
R^2\sin\left(\theta\right)^{4}\cos\left(\theta\right)^{3}+R\cos\left(\theta\right)^{4}-\sin\left(\theta\right)=0
$$
Then you solve for $R$ (and then for $r=\sqrt[3]{R}$) and you have two functions in the form $$r_{1,2}\left(\theta\right)=\sqrt[3]{\frac{-\cos\left(\theta\right)^{3}\pm\sqrt{\cos\left(\theta\right)^{6}+4\sin\left(\theta\right)^{5}\cos\left(\theta\right)}}{2\sin\left(\theta\right)^{4}\cos\left(\theta\right)^{2}}}\\
r_{1,2}\left(\theta\right)=\frac{1}{\sin\left(\theta\right)}\sqrt[3]{\cot\left(\theta\right)\frac{-1\pm\sqrt{1+4\tan\left(\theta\right)^{5}}}{2}}$$
(You choose some values for $\theta$ and then you have $r$)
Answer: The question is about the locus of all real points on the curve
$$ y^{4}x^{3}+x^{4}-y=0. \tag1 $$
In such a simple case, move the $y$ to the other side to get
$$ y = x^4 + x^3y^4. \tag2 $$
Define a function
$$ f(x, y) := x^4 + x^3y^4. \tag3 $$
Given an approximation of $\,y,\,$ then $\,f(x,y)\,$ is
a better approximation.
For example, start with
$$ y_0 = O(x^0) $$
and iterate to get
$$ y_1 := f(x, y_0) = O(x^3), \\
   y_2 := f(x, y_1) = x^4 + O(x^{15}), \\
   y_3 := f(x, y_2) = x^4 + x^{19} + O(x^{30}), \\
   y_4 := fx, (y_3) = x^4 + x^{19} + 4x^{34} + O(x^{45}). $$
The polynomial truncations can be easily graphed,
however, the radius of convergence is small and so this
will not give an accurate picture of the entire locus.

Another global method is to assume that one of the
terms  is small compared to the other two and can
be removed without great distortion. Thus, this gives
three modified equations whose solutions approximate
the original locus on portions of the plane.
Consider $\, y^4 x^3+x^4=0.\,$ This simplifies to
$\, y^4 + x = 0.\,$ The locus of solutions is a quartic
parabola for $x$ in terms of $y$.
Consider $\, y^4 x^3 - y=0.\,$ This simplifies to
$\, (xy)^3 - 1 = 0.\,$ The locus of solutions is a
hyperbola $\, y = -1/x\,$ with two components.
Consider $\, x^4 - y = 0.\,$ This is exactly similar
to the first case. The locus of solutions is a quartic
parabola for $y$ in terms of $x$.
You can plot these three curves on the same plane
and note where they transition to each other. That
is, for $\,y>0\,$ the three curves transition into
a single continuous curve. For $\,y<0\,$ only the
first two curves transition into a single continuous
curve confined to the third quadrant.

Define the function
$$ g(x, y) := y^4 x^3 + x^4 - y. \tag4 $$
The curve of interest is the locus of $\,g(x, y) = 0.\,$
Note that since
$$ g(x, y) = (xy)^4 g(-1/y, -1/x), \tag5 $$
that this is the same locus as $\,g(-1/y, -1/x) = 0.\,$
Thus, every $\,(x, y)\,$ solution has a corresponding
$\,(-1/y, -1/x)\,$ solution. This involution is obvious
for the hyperbola $\, y = -1/x\,$ while it swaps between
the two quartic parabolas.
Comment: In full agreement with your second part.
Comment: Very cool explanation on the second part, thanks a lot!


How do I change the interpolation of Nurbs curve so its Bezier?

Question: I'm fairly new to Blender. I know the basics and all, but I want the camera to follow a path, starting slow, speeding up, then slowing down again, but it wont let me change the interpolation, and I'm stuck on F-curves which moves at the same speed from the start to finish.
I don't know if I'm making sense, but I'm not happy and do not know how to fix this.
Answer: To change a Nurb to Bezier:
Select your curve, go in Edit mode, and in the T panel (on the left of your 3D view) > Tools > press the Set Spline Type button and choose Bezier.
It looks like it doesn't work everytime so here is a way: Select your nurb in Object mode and convert it into a mesh with alt C > Mesh From Curve. Then convert this mesh again alt C Curve from Mesh. Now it's a Bezier. As you can see in Edit mode it has a lot of vertices. To simplify, activate the Simplify Curves addon, then select your curve in Object mode and Spacebar > Simplify Curves. Now in the bottom of the left panel (T) play with the Distance Error factor to reduce the amount of vertices. Once it looks good, come back in Edit mode to check out.
To make an object follow a path:

In Edit mode make sure that your Bezier curve goes in the right direction, if not W > Switch Direction.
Put your object at the center of the scene (alt G).
Give it a Follow Path constraint. Choose the curve as Target. Click on the Animate Path button of the modifier. Now the object follows the path.
As the speed is not the one you want you need to delete the curve's self-generated animation: Select the curve, open the Graph Editor, on the left menu unfold the menu until you see Evaluation Time, select it.
Click N to display the right menu, select the Modifiers tab, click X to close the Modifiers > Generator. Now your object isn't animated anymore, but you're going to fix it manually.
Keep the curve selected. In the Properties panel > Data > Path Animation, keep the option enabled. With Frames choose the number of segments that will divide the curve. With Evaluation Time you will decide at what segment of the curve the object will be at the moment you want on the Timeline.
Now open your Timeline, put your cursor at frame 1, play with the Evaluation Time until the object is at the position you want, then insert a Keyframe on the Evaluation Time. Change the position of your cursor along the Timeline and repeat the operation. As you see you can move the object along the curve at the speed you want, you can even make it go backward. In the Graph Editor you can also change the Interpolation type (press T) so that the movements are more or less flexible.
Comment: Thanks for the detailed answer, but your set spline part did not work, it said " No conversion possible." Do you how to fix this?
Comment: I've edited my answer. I hope it will work
Answer: It's pretty easy way to fix that, which works every time. You need to select the Curve, go to Graph Editor, and in the panel under N in Modifiers, you will see Generator. Delete it. Then in Curve properties under Path Animation add Keyframes to the Evaluation Time with values 0 for the first frame and 100 for the last frame of the camera movement and then in Graph Editor you will see action curves with nice Bezier curves and will have all control that you need over the follow path animation.


Password problem--never set one up

Question: I have a new macbook.  I never set up a password, for either my log in or my husband's.  On my log in, if I want to send a picture to the trash, I can do it.  When I am in my husband's log in, it asks for an administrator name and password to perform the function.  I followed the reset password directions, using the installation disc, but kept our log ins without a password, but creating one for the administrator.  Still can't delete photos on his log in, even using "administrator" and the password, and trying my "name" and his, as shown in our user window.  What the heck is up?
Answer: You will need to setup your husband account as an administrator in System Preferences > Accounts. He may currently be setup as some type of limited user.

Password problem--never set one up


How to find 4th degree polynomial equation from given points?

Question: I am trying to find 4th degree polynomial equation from given points. I do not own a graphing calculator so this task is very difficult for me to solve. So far I would out what points I need. The points are
$$(-2, 3), (-8, -5), (-11.5, -1), (3, -5), (9.5, 2), (-10, -3), (-5, -3), (1, -3), (5.5, -3)$$
I know that the format of the equation should be $P(x)=ax^4+bx^3+cx^2+dx+e$.
I tried to find the way to get the equation but so far all of them require a calculator. I really need help with this problem. Any help would be appreciated.
Comment: is tag functional equation good here ?
Comment: Excel will give you the best fit quartic. Plot the points, add a trendline, and do a polynomial fit of degree $4$.  It won't go through any of the points  unless you are very lucky.  If you choose the option show equation on chart you can get the coefficients.  Any numerical analysis text will have a section on linear least squares which will let you find the coefficients with a matrix inversion
Answer: Lagrange Interpolation is the technique most commonly used for this purpose. Just take 5 points and plug them into Lagrange's formula (which I think is best articulated in the Examples section of the Wiki page). Assuming all of your points do indeed lie on a polynomial of degree 4, you will get that polynomial via Lagrange interpolation.
Comment: On a computer, Lagrange interpolation should never be used except for very low degree polynomials, because of floating point precision issues. Additionally, polynomial *interpolation* (i.e. selecting a polynomial that actually *passes through* all the given points) will not generally answer the question of fitting a polynomial of degree $k$ to a data set of more than $k+1$ points, because typically no such polynomial exists.
Comment: @Ian. 1. Could you show example of such precision issues ?
Comment: @Adam It's a bit tedious to explicitly write down an *example*; this is generally covered in some detail in undergrad numerical analysis texts, e.g. the one by Tim Sauer. But the gist of it is just subtracting of nearly equal numbers. It is also slow to evaluate a polynomial interpolant in the Lagrange form, and it is slow and numerically unstable to convert it to a standard form. The Newton form turns out to be quite a bit more stable, and its form is immediately conducive to the use of a faster method like Horner's method for the evaluation.
Answer: Before doing anything, I felt that there is a serious problem with the data for which you want to find a fourth degree polynomial supposed to fit them.
$$\left(
\begin{array}{cc}
x & y & \text{note} \\
 -2. & +3. \\
 -8. & -5.  & * \\
 -11.5 & -1. \\
 3. & -5.  & *\\
 9.5 & +2. \\
 -10. & -3. & **\\
 -5. & -3. & **\\
 1. & -3.  & **\\
 5.5 & -3. & **
\end{array}
\right)$$
In order to go (more or less) through the data points, you would need a much higher degree.
For sure, since there are $9$ data points, a polynomial of degree $8$ will make a perfect fit but any lower degree will do a quite poor job.
In any manner, the problem has to be treated using multilinear regression.
Using a fourth degree polynomial, the predicted values would be
$$\left(
\begin{array}{cc}
x & y & y_{calc} \\
 -2. & +3. & -0.25\\
 -8. & -5.  & -4.20 \\
 -11.5 & -1. & -0.85\\
 3. & -5.  & -3.16\\
 9.5 & +2. & +2.31\\
 -10. & -3. & -3.75\\
 -5. & -3. & -1.88\\
 1. & -3.  & -1.33\\
 5.5 & -3. & -4.90
\end{array}
\right)$$
Comment: @Adam. Just trying to underline points where you have the same value of $y$. Just looking at the last four data points reveal the serious problem.
Comment: What means the asterices in your first  matix ?
Comment: I like your exposition very much! :-)
Comment: @GottfriedHelms. Be sure I appreciate your comment. Cheers :-)
Answer: @Alex : There is no need for a calculator to draw 9 points on a graph.

You wrote : I know that the format of the equation should be $P(x)=ax^4+bx^3+cx^2+dx+e$.
Well, from what do you know this ? Is it in the wording of your exercise ? You should have given more information. Without one cannot show you the better way to solve your problem.
If it is asked for finding a good but approximate fit of the fourth degree polynomial curve to the points, the regression method is recommended. It can be computed without calculator, but this would be very tiresome. I will not discuss more about the methods to apply because several answers were already given on this subject.
If it is asked for finding a fourth polynomial curve passing exactly on the 9 points, it is impossible. It is obvious just looking at the graph. Nevertheless, a proof is shown below :
We see that four points have the same value $y=-3$. Changing of function $Y(x)=y(x)+3$ shows that the four points are at the four roots of the function $Y(x)=c(x+10)(x+5)(x-1)(x-5.5)$.
So, the four points are exactly on the curve
$$y(x)=-3+c(x+10)(x+5)(x-1)(x-5.5)$$
To make a fifth point $(x_5\:,\:y_5)$ exactly on the curve :
$$c=\frac{y_5+3}{(x_5+10)(x_5+5)(x_5-1)(x_5-5.5)}$$
The equation of the fourth degree polynomial is :
$$y(x)=-3+(y_5+3)\frac{(x+10)(x+5)(x-1)(x-5.5)}{(x_5+10)(x_5+5)(x_5-1)(x_5-5.5)} $$
The figure below shows the five cases : On each one, they are five points exactly on the curve and of course four remaining points far from the curve.
Answer: What you need is a linear least-squares fit. Don't be deceived by the name, "linear" means linearity in the polynomial coefficients $a,b,c,d,e$, not linearity in $x$. If you insist on solving it by hand, you'll need to solve a $5\times 5$ set of equations, which is time-consuming but not impossible.


Knee pain when squatting

Question: I have mild knee pain in my left knee only whenever I have a small break in form when doing any squat type exercise (ie, my knee goes past my toes when my feet are flat on the floor). When in proper form, the knee is pain free and this does not happen to my right knee at all, regardless of form. I have no pain in the knee when not exercising (ie standing, going up stairs, etc) but am worried that I may be setting the ground work for a future knee injury. I wish I could always have perfect form but this isn't possible, say, on the last 2 reps of my last heavy set. I keep proper form >90% of the time. Once the pain hits and I correct my form, it goes away. Also, I cannot take ibuprofen b/c of a reoccurring stomach issue.
Should I be concerned? Since it is in one knee only will it continue to get worst or will exercise strengthen the joint? Should I be doing other exercises to strengthen my knee or go see a doctor? I squat once a week and do jumping exercises ones a week. I also deadlift ones a week so 3 days a week I have this issue.
Comment: I don't want to take away from the main question, but just wanted to mention that knee past toes is not necessarily poor form (common myth among non-lifting PT types) - in fact, it's probably necessary for good form! Otherwise, hard to keep balance & the right structure with load bearing over the center of your foot. Just try to squat below parallel with your toes (and therefore knees) against a wall!
Comment: Here are few questions on knee pain while performing squats. [1st question](http://fitness.stackexchange.com/questions/3660/persistent-mild-knee-pain-due-to-squats-push-through-or-stop) [2nd question](http://fitness.stackexchange.com/questions/6902/pain-just-above-knees-after-squats) [3rd question](http://fitness.stackexchange.com/questions/6281/right-knee-hurts-on-squat). Please check if your question is related to any of these.
Comment: I just want to recommend [this](http://www.runningwritings.com/2011/09/injury-series-tendon-remodeling-part-ii.html) article because it helped me.
Answer:
I wish I could always have perfect form but this isn't possible, say, on the last 2 reps of my last heavy set. I keep proper form >90% of the time.

I think the proper answer to this question is to do everything in your power possible to maintain proper form at > 99.9% of the time.  If that means dropping the weight, then do so.  Gutting out those last few reps on your heaviest sets with poorer technique is not worth the potential damage it will do.
If you really are intent on attempting those last few reps at increased weight, then make sure you always have a spotter to help you squat.  Mentally this allows you to focus on your technique and not worry about failing or cheating because your spotter, assuming the spotters knows what to do, will be able to let you finish.
Answer: The solution is in your question. You have pain only when you lose form, so the solution is obviously keeping good form. If you lose form towards the end than you are simply not concentrating, I don't believe it is muscular. Before the last sets take a slightly longer break (get your pulse down), then focus, and lift. Also, stop looking at the hot chicks! (it never helps my form anyways)
Remember that you don't necessarily feel any pain when losing form, therefore setting ground work for and injury is always a risk. Be smart be safe, good form is not optional!
Answer: A person with average geometry should generally track the knees over the toes if they are performing more than a half-squat. Contrary to the common dogma, there is nothing inherently dangerous about it, and it is in fact the standard technique observed by all professional weightlifters.
That said, no, you should never accept this kind of pain as being part-and-parcel of your training. Nor should you seek to mask pain with analgesics. Something is wrong.
The most common cause of knee pain during squats is associated with but not caused by the position of the knees relative to the toes. The problem is most commonly caused by insufficient activation of the posterior muscles of the leg—hamstrings for knee stability and gluteals for hip extension—and consequently excessive work on the knee extensors (quadriceps). That is, the lift is performed with disproportionate knee extension and insufficient hip extension, resulting in excessive patella compression and pain. The problem can be compounded by lateral instability of the knee, causing imbalances of tension on the patella tendon.
Ensure that your hips and knees are even. In the mirror, your knees should be at the same height and same anterior (forward) position. Activate your hamstrings by maintaining a neutrally anterior pelvic tilt and natural curvature of your spine, particularly in the lowered position. Since the hamstrings are a multi-joint muscle group, they contract more or less isometrically throughout due to simultaneous hip and knee flexion. This contraction, therefore, does not contribute significantly to controlling the load, but rather functions to stabilise the knees. Neutral anterior pelvic tilt also allows the activation of the gluteal muscles, and this should be capitalised on by driving powerfully from the hips. The glutes should feel as though they are working as hard as the quadriceps, and more from the bottom of the lift.
A good heuristic to keep your position is to distribute your weight on your feet evenly or slightly towards the heel. There should be no travel of the pressure distribution across your feet during the movement. And of course, do not hesitate to play with the position to feel what avoids the pain.
I hope that helps.
Answer: Your knee is so important. If this were me, I would do two things. First I would lift lighter, as this means it will put less stress on the knee. If you do this and it still hurts, then you should go see a doctor and let them x-ray the leg to see what's going on. But like I said, look after your knee - it's so important!
Answer: It sounds like the knee is borderline on inflammation problems.  Inflammation happens when a joint is under stresses it isn't ready to handle or is not designed for.  Our bodies were made to squat, and it's an innate ability toddlers possess.  The question is what is causing the inflammation?  Here are possibilities I've run across:

Working too heavy all the time
Way too much volume
Subtle technique issue exposed by heavier weights
A different exercise is causing the problem that is being exposed by squats

If you are constantly pushing or pulling weights in the 90+% range of what you can do, you are just going to grind yourself down.  It is important to hit those weights periodically, but not as a mainstay of your training.  Your joints need a break from the heavy weights so they can also get stronger.
By the same token, there's a limit to the amount of volume your body can take at once.  Prilepin came up with a table where he found his weightlifters were able to still make the best progress without killing themselves in the process.  This is a very useful tool to help prevent over-use related injuries (i.e. inflammation).
Form is very important, and as fatigue increases form breaks down.  Sometimes you have subtle imperfections in your form that only come to light when the weight gets heavy enough.  Fix the form issues and many of the problems will resolve themselves.
Sometimes you need to do rehab work.  Rehab work consists of very light weights for a lot of reps.  We're talking weights that don't even register a proper training stimulus, and doing 50-100 reps total.  All that work is designed to flush blood through your joints to remove the inflammation.  They also help strengthen supporting and stabilizing muscles that don't get a lot of attention when the weight gets really heavy.  Body weight or light lunges might help as an assistance exercise.  Or perhaps leg curls (exercise ball leg curls are surprisingly challenging).
Answer: My recommendation would be to train a more knee-dominant form of squatting -- i.e., front squats (for sets of a few reps, around 5-6 only, to not overload the knees).
Front squats force a more upright back angle (relative to vertical), which will place your hips closer to being vertically under the weight (and therefore your knees farther away from being vertically under the weight!)
This will have the effect of creating greater "mechanical advantage" for lifting with the knees than lifting with the hips, which will (eventually) train the body to lead (and primarily direct) with the knees to move the weight upwards. This in turn will actually strengthen the knees, as they will no longer just be relegated to only merely "supporting" the loads of the body (causing wear-and-tear), but will now also play a more major and active role in directing and managing how the body will handle these (likewise supporting the weight in a more comfortable and efficient manner as well).
Answer: I have suffered from knee pain, chondromalacia to be precise... knee pain can be very nasty, can take a long time to recover (and may not do so perfectly).
While I do agree that "proper form" is important, I do not agree that this is the only thing you would need to pay attention to. I think you would benefit from doing pre-emptive rehab work (at least I wish I did it before the pain got bad). Unfortunately it is difficult to say what you need to do exactly without seeing you. Stiff quads, hamstrings, weak vmo muscles can all lead to problems later, and all need specific rehab work. I would suggest that you work together with a good physiotherapist to prevent future problems.

Knee pain when squatting


connect a 12V device to Raspberry pi

Question: I need to connect a 16mm press Push Button Switch flat round Latching Self-locking 1NO 1NC with 12V rating to Raspberry pi3. (https://www.aliexpress.com/item/16mm-Metal-brass-Push-Button-Switch-flat-round-illumination-ring-Latching-1NO-1NC-Car-press-button/32639077602.html?spm=a2g0s.9042318.104.22.168424c4dekMKgp). How can I do that without blowing up the pi?
Answer: If you'll just connect the switch contacts to the RPi then there should not be any problem.
Schematic for what is on my mind

As button has light (probably led) that probably has to be powered by 12V so for that you'll have to connect it by some other means to RPi if you'd like to control that.

connect a 12V device to Raspberry pi


How to find where is $JAVA_HOME set?

Question: I'm trying to change the value of $JAVA_HOME & I just can't seem to find in which file is it being set currently. I can't remember where did I set it the last time.
Already tried How to determine where an environment variable came from? but I need(ed) a list of files where the variable can be set.
Answer: You didn't specify a shell.  So, I will assume bash.  The next issue is: did you set it for your user only or system-wide?  If you set it for your user only, then run:
grep JAVA_HOME  ~/.bash_profile ~/.bash_login ~/.profile ~/.bashrc

If you set it system-wide, then it may vary with distribution but try:
grep JAVA_HOME /etc/environment /etc/bash.bashrc /etc/profile.d/* /etc/profile

If the above give no answer, you can cast a wider net:
grep -r JAVA_HOME /etc
grep -r JAVA_HOME ~/

See also the suggestions in How to determine where an environment variable came from.
Comment: Thank you for responding. Couldn't find this variable in any of these files. Btw, I'm on Ubuntu (if that matters)
Comment: For clues, please check (a) if you log in as a different user, is JAVA_HOME still set? (b) If you reboot, is it still set?  This search can be complicated because any of the files I listed can source other files of their choosing and JAVA_HOME could be set in any of those.
Comment: Sorry, my bad.. I had set it in ~/.bashsrc but the changes didn't show up since I used different terminal instances to set & test the value of variables. Thanks for your help.
Answer: With zsh:
zsh -xl

In bash:
PS4='+$BASH_SOURCE> ' BASH_XTRACEFD=7 bash -xl 7>&2

That will simulate a login shell and show everything that is done (except in areas where stderr is redirected with zsh) along with the name of the file currently being interpreted.
So all you need to do is look for JAVA_HOME in that output. (you can use the script command to help you store that output).

How to find where is $JAVA_HOME set?


Cannot boot into Windows after Ubuntu 16.04 install

Question: I am unfamiliar with Windows UEFI and changed the BIOS to Legacy to get my Lenovo B50 to boot from a USB port to install Ubuntu. Now the only way I can boot is to use UEFI in the BIOS to boot Windows and change it to legacy to boot Ubuntu. How can I fix this? Thank you in advance for your input.
Comment: I don't think you can have a permanent solution while mixing the two boot systems.  you should decide which OS  you want to reinstall to be like the other.
Comment: Possible duplicate of [Installing Ubuntu on a Pre-Installed Windows with UEFI](http://askubuntu.com/questions/221835/installing-ubuntu-on-a-pre-installed-windows-with-uefi)
Answer: On my system I use F2 for UEFI, F8 for Boot Options and F10 for recovery. Yours likely has a boot option, too. What this does, is when I boot using F8, it pulls up my Win Boot Loader, Ubuntu USB and Ubuntu Boot-loader partition. After installing 16.04 (and until I get this grub2 fixed) I have to boot with F8 and choose Windows or Ubuntu respectively to boot into mine manually. Note, I am unable to do this when Secure Boot is active, so use F2 (UEFI option) and disable Secure Boot and see what happens.


Off-kilter design style

Question: I'm trying to recall what this style is called where it's super minimal, there's a light use of shapes to guide the attention and the shapes and text are slightly out of kilter to each other. Does anyone know what this is called?
Comment: Maybe look into Swiss or International style?
Comment: Material Design?
Answer: I would call it ultra contemporary or minimalist with hierarchal and visual weight.
It looks very "Bauhaus". Their design philosophy revolved around things being:

minimalist
geometrical
anti-ornamental
hierarchical

Off-kilter design style


Ubuntu 16.04 systemd user service anomaly

Question: I have enabled and started a user service (systemctl --user enable serviceName... etc.).
But when I log off, the service stops. Why?
I have made a similar user service on Fedora 22 before, but that doesn't stop when I log off.
Is there any workaround for this?
Answer: It might be even better:

The systemd user instance is started after the first login of a user
  and killed after the last session of the user is closed. Sometimes it
  may be useful to start it right after boot, and keep the systemd user
  instance running after the last session closes, for instance to have
  some user process running without any open session. Lingering is used
  to that effect. Use the following command to enable lingering for
  specific user:
# loginctl enable-linger username

https://wiki.archlinux.org/index.php/Systemd/User
Comment: Thank you so much! You saved my day!
Answer: Systemd user services only last as long as a user's session does. This means you must be logged in for a user service to operate successfully.
In Ubuntu, your session ends when you log out of X, and all terminals (TTYs, local, and remote). I would assume Fedora kept a user session open for you.
For Ubuntu, I would suggest that you create a system-level service and then tell it to run as a specific user. You can do this by setting User= and Group= in the [Service] section of your file. If you want to just have write access on that user account, I would suggest you set appropriate file permissions.
Finally, if you want to make it so that a service starts only when a user tells it to, you can use the instructions from this AU post.
Comment: Not quite.  Per-user services only last as long as the per-user service manager does, an important distinction.  That _might_ be only as long as there's any login session for that user.  But one can configure `systemd-logind` so that that is not the case.


Is is possible CONCATENATE 2 Choice columns? We want to display the descriptions next to the choices

Question: Is it possible CONCATENATE 2 Choice columns?  We want to display the descriptions next to the choices. There are 5 choices for the user to pick from in a New Item form.  The boss wants an elaborate description next to (to the right) each choice. I thought maybe I could make another choice column w/ the descriptions, then another calculated concatenated column to join them. Is that possible or reasonable? We have a no-code rule, so I can't use Designer or InfoPath. Thanks!
Answer: 1) Create a separate list
2) Add a calculated column (e.g. Full Title) with the following formula:
<code>=CONCATENATE([Title]," - ",[description])
</code>

3) Use Full Title column as lookup column
Answer: Try using a lookup column.  Make another list with your items and descriptions.  Then make a lookup to that list and select the description column for "add a column to show".


Disappeared question

Question: My question Dark matter as invisible part of the Heisenberg's universal matter (asked 27 October) disappeared with no trace from my SE site together with its upvotes. How can I know what happened?
Answer: Your question (10k link only) was deleted by the "Roomba", which is an algorithm that automatically deletes old questions which have a negative score and meet some other criteria. The details are listed in the help page I just linked. Specifically, the question you're asking about satisfies the following criteria:

If the question was closed more than 9 days ago, and ...

not closed as a duplicate
has a score of 0 or less
is not locked
has no answers with a score > 0
has no accepted answer
has no pending reopen votes
has not been edited in the past 9 days

... it will be automatically deleted. These are "abandoned closed", and are termed as RemoveAbandonedClosed.
This check is run every day across all sites.

In general, when something odd like this happens, it's good if you look around the help center and meta faq posts (here and on Meta Stack Exchange to see if you can find an explanation. If you don't, then asking on meta, as you did, is the thing to do.
Comment: Still my question was posted on 27 October and deleted on 18 November, therefore it was not more than 30 days old, and in plus this question received meanwhile two upvotes.
Comment: See my edit for further details.
Answer: It should still be available through your profile, but if it has been deleted by the roomba then it is hidden. To find it, go to the bottom of the questions tab of your profile and look for a link to deleted recent questions:

Questions are normally visible through that link for sixty days; after that, they remain visible if you are the owner (or you have 10k rep) and you have the URL, but they are not linked to anywhere on the site.

Disappeared question


Where can I find class 3 gimballed multi-cannon?

Question: I've been to lots of high tech, high population systems looking for 3 gimballed multi-cannon. Where can I find them in Empire space (without a permit, as my Empire ascension is bugged at the moment)? Do they exist? If not do we have any confirmation from the devs that they're not supposed to (i.e. they aren't just really rare).
Comment: I believe these do exist now in Engineers 2.1
Answer: There are no class 3 (large) multi-cannons, railguns, missile racks, torpedo pylons, mine launchers, or mining lasers.
I believe that's because a class 3 multi-cannon would be too powerful and would unbalance things. Same with some of the other weapons lacking a class 3 variant. (Though some might lack a class 3 variant because it seemed unlikely to be useful).
For class 4 (huge), there are only cannon and plasma accelerator.
Comment: Cheers (+1) for the ans do we have any actual confirmation of that? Especially on the weapon balancing, as there are things like class 3 beam lasers that are at a similar level, and weapons like missiles that seem to have started overpowered, been nerfed to uselessness and then just left.
Comment: I can't find confirmation of the reasons for a C3 MC to have been left out or dropped, but here's something from one of the game designers that hints at it (in a discussion about maybe creating a C3 weapons between cannon and multicannon): https://forums.frontier.co.uk/showthread.php?t=130531&p=2000151&viewfull=1#post2000151
Comment: However, the large Beam has a high thermal load and draws a lot of power. If you put a pair of large beams on a Vulture (with best power plant and distributor) it won't be able to sustain fire for long, and it will greatly limit your ability to equip and use other power-hungry things (like high rated thrusters, high rated shields, shield cells, shield boosters, etc). Since in class 2, the MC has 1/4 the thermal load of the beam and about half the power, a pair of class 3 MCs would probably be *just too awesome*.