How do Pokémon "Sightings" work?

Question: With the new update, we now have "Sightings." However, there is no indication of how this differs from "nearby Pokémon", though in the patch notes, it states they are testing a variation of "Nearby Pokémon" which appears to be the "Sightings." How do "Sightings" differ from "Nearby Pokémon"?
Comment: If what I see is true, they no longer show dups. I was so tired of seeing 9 Pidgeys near by all the time
Answer: The nearby system was originally supposed to show you pokemon spawns in order of distance (Which we all know didn't work at all). Essentially Sightings is now a list of what pokemon are currently in the area as opposed to listing every nearby spawn as an individual pokemon, which also caused a bunch of duplicates to clutter the tab. They also took out the ability to "watch" a pokemon since that was based on distance as well. Sightings doesn't appear to sort pokemon in any particular order, at least not alphabetically or numerically based on pokedex number. (For example mine currently shows Drowzee #96, Weedle #13, Ratata #19, Pidgey #16 etc.)
It also seems to update more frequently and accurately, every 15 seconds. Previously with the nearby system I would have to force close the app and reopen it to load a new nearby list (Personally I don't think it was properly removing pokemon from the list if they despawned). The new sightings system removes pokemon that are no longer currently in the area. This combined with the fact that there are no more duplicate listings, means the tab is less cluttered and more reliably showing what is actually around you.
Comment: I can attest to the old one not removing Pokémon that were no longer in the area. So basically the new one is taking the pieces that kind of worked in the old one and adding a slightly different UI around it.
Comment: Sightings do sort by distance as far as I tested. Also, your last paragraph is correct -- the non removal was a bug that was fixed in 0.33
Comment: Well actually I think it sorts by something like distance or by distance zones. It actually now shows the pokemon you just spot by you on big map and it actually is in the 3 "top" shown in small panel, so I would say it sorts them by distance. At least it seems. However it is still probably highly experimental, I hoped that the "grass" will change color or picture depending on biome, but no. And yes, it updates pretty fast, especially when you catch pokémon, it instantly hides. So let's see what they will do with it :)
Comment: It doesn't sort by distance. I had a list of 5/6 this morning, and a Venonat popped up right outside my house, but it was 5th in the list (i.e. the centre position). Still no decent sorting

How do Pokémon "Sightings" work?


how can I move account owner alias field from the data loader

Question: I have moved all the account data in another org through data loader but in the account owner alias field it is showing admin, I have to show the user perspective shot name. Thanks in advance
Comment: Does it also show the admin as the account owner?
Comment: Are you importing the account owner field in data loader? Do all of the users exist in both the source and target orgs? If the users do exist you would need to map the id from the source to the target on the owning users probably by matching names in text format.
Answer: The Account owner's alias is part of the User record that's linked through the Account's OwnerId relationship. If you did not load the OwnerId field when you did your data load (which sounds like it is the case), the running user for the data load was automatically assigned ownership of all of the records.
To fix this, you'd need to obtain the original ownership data from your source org and perform a Data Loader update. To do so, you'll need to use the success file provided by Data Loader to map the Ids in the data from the source org to the new Ids in the destination org using a VLOOKUP() or INDEX/MATCH() construction in your spreadsheet. This would allow you to create an update file with the new Id and the old OwnerId for each Account and thence perform an update.


As Part of JMeter WEB DRIVER(Selenium Scripts) IntegrationWith Azure Pipeline and how can I add jp@gc- chrome config sampler in Azure Pipeline

Question: As Part of JMeter WEB DRIVER(Selenium Scripts) Integration With Azure Pipeline.I have pushed the scripts into Azure GIT Repository  and how can I add jp@gc- chrome config sampler in Azure Pipeline? Normally we add jp@gc - Chrome Driver Config in follwing way https://stackoverflow.com/questions/44428349/jmeter-jpgc-webdriver-sampler but when it comes to adding in Azure Pipeline? Could anyone please help me
Answer: Chrome Driver Config is a part of WebDriver Sampler
You do have it already, however it looks like you made a typo, it should be jpgc-webdriver and you have a whitespace there

Also make sure that your test is suitable for headless execution as there will not be GUI on the Azure runner


Master pages through design manager, how to manage different sharePoint controls on different places in the master page

Question: In SharePoint 2013, Client has a requirement to place different SharePoint controls on different places in the master page. How to control this situation when through design manager we can manage how to place different SharePoint controls on different places in the master page?
Answer: In SharePoint 2013, you have the flexibility to use HTML file to edit the master page and it will be converted to .master file automatically.
That means you can edit the .html version of master page in any Editor (Text editor or Html editor like Notepad++, Dreamweaver, Visual Studio etc.). During editing you can place different SharePoint controls on different location and upload this .html file in SharePoint master page library with correct content type. From design manager you can convert your .html version of master page to .master file and check preview. On preview you have the option to move to Snippet Gallery, this gallery allows you to generate SharePoint controls to place in .html version.
Comment: can you put SharePoint controls in dream weaver or notepad++? I don't think so.
Comment: Snippet Gallery will give you code snippets for SharePoint controls that you can use in dreamweaver or notepad++ (in fact any editor). This is new feature in SharePoint 2013.
Answer: Yes you can, You need to build custom master pages using visual studio 2013. deploy the wsp to server.
Comment: Great that you know this. Could you elaborate on the answer explaining in further detail how this should be done? It will be more helpful if you do. Thank you!


How to image a GCE instance with multiple persistent disks

Question: I'm looking for a way to snapshot/image a Google Cloud instance that uses multiple disks.  From what I've found so far, this does not seem to be supported, as I haven't seen a way to create an image that references more than one disk.  I'm surprised if this isn't available, as Amazon has had that functionality for a long time.  There you can simply issue a command to create an image from an existing instance, and it will automatically snapshot all disks attached to the instance and include them in the image, such that launching a new instance from the image creates all new disks based off the snapshots.  Is there a way to do this easily in GCE that I am missing, or does it just require custom scripting?
Answer: The only option at present is to create snapshots/images of the VM Instance boot and the additional disks, however there is a feature request so that this feature can be made available in the future. There is no ETA but any updates can be checked on this link above.
Answer: Hello Aosoft,
           Not sure, if you already figured this out as its been a while. I came across it and I am using instance templates for this.
Need to create an image of each disk in VM and then group them as instance template. Use that instance template to provision new VMs.
Thanks
Answer: Below command create image for the whole instance (all disks)
gcloud beta compute machine-images create instance-image ....

Detail can be found here: https://cloud.google.com/sdk/gcloud/reference/beta/compute/machine-images/create
P/s: It's different from the below command which create image for one disk only
gcloud compute images create ....

Hope that help...


Does the fact that the TDZ is not written for runway 22 means there are touchdown zone lights only for runway 04?

Question: Does the fact that the TDZ is not written for runway 22 means there are touchdown zone lights only for runway 04?
Answer: According to the Jeppensen Airport Chart Legend (p. 3) all operational runway lighting are listed.
So I assume RWY 22 has no, at least active, TDZ lighting.


If supervisor has no expertise in your research work, is it possible to do a PhD under that supervisor?

Question: In my PhD, I am assigned mathematical modeling topics and my supervisor's work is related to mathematical biology. But I don't want to work in mathematical biology. Because actually there is not so much real application of that and I don't like biology. Instead, I want to work in fluid dynamics. But my supervisor's research area is totally different. Is it possible  to do independent research work without supervision of supervisor?
Comment: A strange question. Who "assigns" topics? Why do you have an advisor doing something different than what you want? How did this state arise? No, it's not good to have an advisor who cannot give you expert advice, nor write a knowledge-able letter later, ... How did this state arise?
Comment: But there are plenty of topics in mathematical biology that require fluid dynamics.  //  Frankly, I don't understand how you ended up with a supervisor who does mathematical biology if you dislike mathematical biology.
Comment: I found myself in a situation with distinct thesis supervisor and lab director (in different states from each other).  The thesis supervisor still provided me with a LOT of non-technical guidance that enabled me to finish, but the lab director was the one for day-to-day experiment design and discussion.  (And a third committee member was much more versed in foundations of the computational method I ended up defending than either of those).  So don't look at it as "independent, without supervision", but that the supervisor is providing advice in only a subset of the "normal" ways.
Answer: In summary: is it possible? Yes. Should one do it? No.
You need an advisor to tell you which problem is important to solve, which direction may not be feasible to investigate, which conference to submit your work etc etc. If you have to do all these alone, you may waste years going nowhere.
That being said, I happen to know a couple of people who successfully did their PhD without working with their advisors. All are very talented, and extremely confident with their research. One of them is a very young PhD student in my former school, who has published 3 solo papers (and co-authored some others), and invented a new sub-field of cryptography.
Comment: Would add that ideally, a supervisor introduces you into the community — how they work, what is important, etc. The things you can only infer from papers. And you need to become part of the community to get crucial information. It is very hard to do this without help. Also, how can a supervisor grade the work without domain expertise? This being said, some supervisors jump on "hot topics" they know nothing about — which is rarely good for the PhDs.
Answer: You need someone to help you with the technical side of your work, and that person needs to be an expert in the field (remember, for a PhD you need to do new research, which google won't do for you).
However, the person who supervises you in practice does not ultimately have to be your supervisor in name. One option to consider would be co-supervision, so one supervisor brings experience of academia and research, while another brings technical knowledge. If it works out, that can also be a benefit to a young academic who is new to supervision. I've also known people whose supervisors were sufficiently absent that they weren't really much use. Much of the supervision was actually done by postdocs who were working in the same lab.
Answer: No, this is not possible.
Having a supervisor is not some formal paperwork you need to do to please the management. A supervisor exists for a reason. If you work alone, your work in fluid dynamics is unlikely to be successful. Most probably it will be about "reinventing the wheel", as proposing a doable topic with the potential of scientific novelty requires lots of competence. You cannot have also your PhD defence without the competent opponents; they will come and may find lots of issues.
A supervisor may only be partially competent if the project bridges multiple disciplines. For instance, if you are doing mathematical modelling in biology, your professor may be highly competent in mathematical modelling or in biology, but maybe not in the both areas at once. Also difficult but I have seen this working, and professor should normally try to arrange at least some co-operation with researchers competent in the complementing area (how successfully, another question). However simply ignoring the supervisor and going just on your own does not make any sense.
Answer: Theoretically speaking it is possible to do a PhD under a supervisor who is not an expert in your area but it can get very difficult for times when you need help and "supervision." PhD students are not completely independent researchers and generally follow the directions set out by their supervisors. So if you really want to do something different, the best way would be to change supervisors.
Comment: @RonobirSarker, online help (e.g.SE sites) can be invaluable for some details, but you'll require hands-on, face-to-face help much more. Besides, your advisor/people of the research group/lab supervisor/... *do* have (some) interest in your work, random SE folks don't.
Comment: So is it not possible to take online help of my area?
Answer: It depends on the field.
Just as a positive example from my field, I know people in geophysics who regularly do PhDs and research based masters with people who have little knowledge of their specific project at the start.
For example, one of my colleagues is doing a PhD with a very very well known geophysicist, who is known more for is observational and experimental work, but has developed a modeling project with him. Because my colleague has very strong computer skills, and access to advice from other people, the actual "modeling" part he doesn't need as much advising in as the actual general scientific skills. In my opinion, his dissertation  work has turned out to be very good because of this, with many more productive collaborations than the normal PhD students tend to have out of necessity. Another strong point about his program is that because he is using unusual methods for his lab, he already shows strong independence from his PhD advisor, which might look good on job applications.
So I will say that it might be smart to do this depending on the quality of scientist you are at the beginning of your PhD work, and the quality of your advisor. These are two things that are very hard to evaluate, and I think that it turns out bad more than it turns out good, but there is clear upside and potential to create a truly unique educational experience regaurdless.
Answer: Is it appropriate to change supervisors due to lack of expertise in the field? Any hard feelings?
Doing a research under one who doesn't have a good understating about the topic is one lonely journey.
Comment: Upvoting, not because I think this answer is particularly good but because I think the negative comments from review are particularly bad. The idea that this is a new or different question seems to come from seeing two question marks and not reading the words that precede them.
Answer: I think it's easier to do this in experimental topics than theoretical ones.  Big physical lab groups really have little supervision, apprenticeship anyways.
Overall, it is going to depend on how independent you are, how feasible the problem is (pick something doable).  Also that the advisor is at least not an active hurdle--it's one thing if you pull your own sled but if you have someone fouling the runners?


What is "Janus"-linking?

Question:
How did it get its name?
The attacker can't actually steal Monero, right?
It relates to a clever use of cryptography involved in subaddresses? How so?
Can it be mitigated?
Answer: (The Janus attack referred to in this question is documented here: https://web.getmonero.org/2019/10/18/subaddress-janus.html)

We were looking for a character from Greek mythology that had multiple identities. This is because the Janus attack allows an incoming transaction to appear to be addressed to one wallet subaddress, while having actually been addressed to a different wallet subaddress during transaction construction. Sarang Noether of the Monero Research Lab suggested Janus, who was a "two-faced god".
No, they can only attempt to trick the recipient into revealing control of two different subaddresses.
The link at the top of this answer documents the elliptic curve algebra. In plain English, the subaddress system is designed to allow a wallet to efficiently scan for incoming outputs to multiple subaddresses within the same wallet (i.e. where the subaddresses share the same private view key). A side-effect of the way in which the subaddress system was designed to allow this efficient scanning is that the wallet will trust the sender to inform the wallet of the particular destination subaddress. This trust was an oversight during the design of the subaddress system.
Yes, there are several ways to mitigate it, but these have not been decided upon yet. One way is for an update to the transaction construction to include a signature that proves the transaction was properly constructed for a particular subaddress destination. Since this modification will add perhaps 64 bytes to the size of a transaction, there will be careful consideration of a mitigation to ensure it is done in the most space-efficient way possible.

What is "Janus"-linking?


Why did lord Rama take help of Sugriva?

Question: What is the significance of Lord Rama seeking help from Sugriva? As Lord Rama is avatar of Lord Vishnu so I think he might know who abducted Sita Mata and where he kept secondly it was his personal matter so why did he involve Sugriva and his army when he alone is sufficient to destroy Ravana and all other demons? Why did Vanara Sena suddenly come into picture?
Answer: Rama took the help of Sugreeva in order to allow Sugreeva to fulfill his own promise to Rama and hence to save Sugreeva from the sins for making fake promises
You can find that Sugreeva promised to Rama that he will fetch Sita from the following slokhas

Then Sugreeva who is gladdened again spoke to Rama of Raghu's dynasty, "My best minister and this servant of yours Hanuma informed me of the reason for which you have come to uninhabited forests along with your brother Lakshmana, and that while living in the forest, and when you and this courageous Lakshmana are not her alongside a demon stole your wife Maithili, the daughter of Janaka, wailing as she was And he also said about that arch demon's killing an eagle named Jatayu on waiting for an opportunity, and his causing an agony in you by way of  separating your wife. Before long you will get rid off your agony caused by the separation of wife, for I will fetch her very soon, like the retrieval Vedic Scriptures. Oh! Enemy destroyer, Rama, I will fetch your wife to give her to you whether she is in netherworlds or even in empyrean worlds...."
[1-6, Sarga 6, Kishkindha Kanda, Valmiki Ramayana]

Although Rama can do the task alone without any help of Sugreeva, he just waited for allowing Sugreeva to fulfill his own promise to Rama. You can get it from the following words of Hanuman to Sugreeva

"Hence, the task of our friend is delayed, oh, enemy-destroyer,
searching for Vaidehi is Raghava's mission and let it be done. Though
the time is lagging, oh, king, that insightful and punctual Rama is
not indicating about it to you, though he is hurrying to complete his
mission within a time-frame, because he is following you alone abiding
under the control abiding by your promise........... If need be Rama
of Dasharatha is really capable of keeping gods, demons and
great-vipers under his control with his arrows, but he is anticipating
fulfilment of your promise"
[15, 16, 22, Sarga 29, Kishkindha Kanda, Valmiki Ramayana]

If Sugreeva does not fulfill his promise, then he gets the sin of suicide along with the sin of killing his own kith and kin. In order to avoid it Rama took the help of Sugreeva by allowing him to fulfill his own promise. The following slokhas by Lakshmana to Sugreeva can clarify it

"A person gets attached to the sin of killing of a hundred of his manes, deified souls of his own ancestors, if he promises to gift one horse but fails to do so, and in promising to gift one cow but failing in it he gets the sin of killing a thousand manes, and if he promises to a person to do the needful help and fails in rendering that help, then he gets the sin of suicide along with the sin of killing his own kith and kin...."
[9, Sarga 34, Kishkindha Kanda, Valmiki Ramayana]
Answer: While searching for Sita, Sri Rama and Lakshmana had an encounter with Kabandha.  After incinerating him, he resurrects in a celestial form and advises Sri Rama to befriend Sugriva, who can cause search for Sita through his vanara army.

शृणु राघव तत्त्वेन यथा सीमाम् अवाप्स्यसि || ३-७२-७
  राम षड् युक्तयो लोके याभिः सर्वम् विमृश्यते |
  परिमृष्टो दश अन्तेन दश आभागेन सेव्यते || ३-७२-८
"Oh, Raghava, how you will regain Seetha, that you listen from me in its essence... oh, Rama, by which and which analyses everything will be analysed, six of such ideations are available in this world... and when a person is touched down by a spell of nemeses, he shall adore one who is equally in such spell of nemesis... "
तत् अवश्यम् त्वया कार्यः स सुहृत् सुहृदाम् वर |
  अकृत्वा न हि ते सिद्धिम् अहम् पश्यामि चिन्तयन् || ३-७२-१०
"Oh, best among kind-hearted ones, thereby you have to certainly befriend such a soul in similar dire straits... however deeply I may think, I am not able to perceive your accomplishment if you do not befriended with such a soul."
यताम् राम वक्ष्यामि सुग्रीवो नाम वानरः |
  भ्रात्रा निरस्तः क्रुद्धेन वालिना शक्र सूनुना || ३-७२-११
"Oh, Rama, listen what I tell... a vanara is there by name Sugreeva, who is vengefully reneged by his brother Vali, the son of Indra."
स ते सहायो मित्रम् च सीतायाः परिमार्गणे |
  भविष्यति हि ते राम मा च शोके मनः कृधाः || ३-७२-१५
"Oh, Rama, he will be your associate and an aid in searching for Seetha, and he conducts himself in your wellbeing, hence let not your heart yield to agony."

Sage Valmiki described Sri Rama to be a human only, but not as incarnation of Vishnu.  Sri Rama was undergoing a bad spell of time and he had to befriend another person undergoing similar bad spell of time.
It is an acceptable policy among kings.
First Sri Rama helped Sugriva and then Sugriva helped Sri Rama.
Answer: The main reason is that a Gandharva of the name of Viswavasu who became a Rakshasa because of a curse told that Sugriva will help him.
https://www.sacred-texts.com/hin/m03/m03277.htm

Thus addressed by Rama, that being replied unto him, saying, 'I am, O prince, a Gandharva of the name of Viswavasu! It was through the curse of a Brahmana that I had to assume the form and nature of a Rakshasa. As to thyself, O Rama, Sita hath been carried away with violence by king Ravana who dwelleth in Lanka. Repair thou unto Sugriva who will give thee his friendship. There, near enough to the peak of Rishyamuka is the lake known by the name of Pampa of sacred water and cranes. There dwelleth, with four of his counsellors, Sugriva, the brother of the monkey-king Vali decked with a garland of gold. Repairing unto him, inform of thy cause of sorrow. In plight very much like thy own, he will render thee assistance. This is all that we can say. Thou wilt, without doubt, see the daughter of Janaka!

Another reason can be this.
The vanaras were born to be the allies of Vishnu. Vishnu incarnated as Rama and the vanaras were the sons of the devas.
Brahmarshis and others complained to Brahma about the same thing.

"Markandeya said, 'Then the Brahmarshis, the Siddhas and the Devarshis, with Havyavaha as their spokesman, sought the protection of Brahma. And Agni said, 'That powerful son of Visrava, the Ten-headed cannot be slain on account of thy boon! Endued with great might he oppresseth in every possible way the creatures of the earth. Protect us, therefore, O adorable one! There is none else save thee to protect us!'
Brahma said that Vishnu is on the work to destroy him and that no god or asura can vanquish Ravana.

"Brahma said, 'O Agni, he cannot be conquered in battle by either the gods or the Asuras! I have already ordained that which is needful for that purpose. Indeed his death is near! Urged by me, the four-headed God hath already been incarnate for that object. Even Vishnu, that foremost of smiters will achieve that object!'
Brahma then asked Indra and other devas to have bears and monkeys as their offsprings so that they will be the allies of Lord Vishnu.

"Markandeya continued, 'Then the Grandsire also asked Sakra, in their presence, 'Be thou, with all the celestials, born on earth! And beget ye on monkeys and bears, heroic sons possessed of great strength and capable of assuming any form at will as allies of Vishnu!'

The gods and danavas then formed a counsel as to how they should be born according to their respective parts.

And at this, the gods, the Gandharvas and the Danavas quickly assembled to take counsel as to how they should be born on earth according to their respective parts.

Brahma also told  Dundhubi to be born as Manthara and cause quarrels.
And in their presence the boon-giving god commanded a Gandharvi, by name Dundubhi saying, 'Go there for accomplishing this object!' And Dundubhi hearing these words of the Grandsire was born in the world of men as the hunchbacked Manthara. And all the principal celestials, with Sakra and others begot offspring upon the wives of the foremost of monkeys and bears. And those sons equalled their sires in strength and fame. And they were capable of splitting mountain peaks and their weapons were stones and trees of the Sala and the Tala species.
Brahma instructed Manthara to cause quarrels.

And the adorable Creator of the Universe, having ordained all this, instructed Manthara as to what she would have to do. And Manthara quick as thought, understood all his words, and went hither and thither ever engaged in fomenting quarrels."

Sugriva is the son of Surya so we can say he was born to be one of the allies of Vishnu's avatar Rama.

Why did lord Rama take help of Sugriva?


Deterministic or stochastic universe?

Question: Just a little bit before my graduation from computer science, I attended a course about computational intelligence, and my professor then challenged us to debate on whether the world/universe follows a deterministic model or a stochastic model. I have never read a single book about those topics and only until recently I started reading philosophical books but since then I have been thinking over it on my own, like ancient greek philosophers would do with all the parameters and consequences involved in each aspect. I have also talked a lot with ordinary people about the subject. For example a murderer is not in fault for his crime in determinism model, in stochastic modeling there is such thing as a free will etc.
Personally, as an engineer I incline towards the deterministic approach and I would also love to hear other people's opinion, debate on the subject and provoke people that support Stochasticism to take a step and present their arguments on why they believe there is randomness in the world, and not just the human's inability to comprehend all the available chaotic finite non-measurable parameters of the system called universe.
Although, lately, with quantum mechanics and the new quantum computer from Google, my firm beliefs took a blow because although computers follow determinism in their functions and systems, Google's PC had a 0.1% error based on indeterminism. I am digging into the issue and may form another question in the stackexchange, but my intuition about this uncertainty leads me to the principal of uncertainty from Heisenberg where you cannot predict precisely both the position and momentum
Comment: Hi, welcome to Philosophy SE. This is a Q&A site rather than a forum, so inviting "to hear other people's opinion, debate on the subject and provoke people that support Stochasticism to take a step and present their arguments on why they believe there is randomness in the world" is explicitly not allowed. Questions here are expected to be specific, pointed, and (plausibly) have definitive and objective answers. It is hard to see a question in your post beyond the debate invitation. You could ask what philosophers said on the issue, or ask for flaws in a specific argument for/against.
Comment: Just a suggestion: I'd take out the about about free will and moral responsibility; the link between determinism and free will and responsibility is hotly debated among philosophers. For example,  plenty will say that in a determinist universe, you can still make sense of the notion of free will, and hence that the murderer really is responsbile, and really is at fault. But, since those debates have nothing to do with your question, I would avoid any such complications by just taking out that little passage. And by the way: can you please break your post up into some logical paragraphs?
Comment: @JohnForkosh - The conclusion about there being no "instruction sets" only applies if you assume that the particles cannot influence each other faster-than-light, and also that there is only a single world and so a single unique outcome of each experimenter's measurement. The 1st assumption is violated in [Bohmian mechanics](https://plato.stanford.edu/entries/qm-bohm/), a deterministic model with local hidden variables that can account for the results of EPR experiments. The 2nd is violated in the deterministic [many-worlds interpretation](https://plato.stanford.edu/entries/qm-manyworlds/).
Comment: Three body problem unpredictability makes black holes sensitive to initial conditions to below the Planck scale, suggesting the universe is not deterministic in terms of being predictable from it's current state https://www.universetoday.com/145463/the-three-body-problem-shows-us-why-we-cant-accurately-calculate-the-past/amp/
Answer: This is an important question, and one that to answer, one must dig into some of the subtleties of physics.
The most common answer one will find is that we thought our universe was deterministic under Newtonian "classical" physics, such that LaPlace's Demon who could know the location and momentum of all particles, could predict the behavior of the universe forever.  But that the development of quantum mechanics in the early 20th century requires that our universe be stochastic.  This was the view of the founders of quantum mechanics theory, who all embraced stochasm.  However, this view is not 100% valid -- there are subtleties about both classical and quantum physics.
Relative to classical physics, several physicists in the last several decades have been exploring "classical" cases which lead to stochastic solutions.  Here is one such reference: https://www.journals.uchicago.edu/doi/full/10.1086/594526?casa_token=jcR7Qn5Ji-cAAAAA:rxtSGXk98L_jfEBttu1Lt2LD3DGjsRXmhk6C_4AcUByNqWdELIjk_3ehV_rhVWe0TM9DbprEJkLj  Note the language is not particularly clear, but for every case where "uniqueness fails" or "there is more than one solution" -- that translates into classical physics having multiple possible outcomes to an event, and thus being stochastic rather than deterministic.  These are recent discoveries, and thus have not been subjected to multiple decades of critique, but the linked paper is a decade and a half old, so there has been a fair amount of time for rebuttal, so far without success.  These are also rare and exotic cases, so classical physics could be described as "mostly deterministic" based on them alone.
Another discovery, a little older but also recent, was that even deterministic models can be unpredictable.  This was first discovered in weather models, where a complex weather simulation code, which was entirely deterministic in character, ended up giving radically different predictions when one of its inputs was rounded off at the 4th decimal place. These are now called chaotic systems, and weather is considered a prime example of classical physics "deterministic" chaos in nature.
A good example of chaotic behavior in a much simpler system than a weather model, is this illustration of chaotic behavior from triple pendulums:  https://jakevdp.github.io/blog/2017/03/08/triple-pendulum-chaos/  Note, one of the beliefs I have heard is that while quantum might be stochastic, our macro universe is not.  The triple pendulums provide an example where that is not the case, because it is SUCH a sensitive system, that variations on the order of the Heisenberg uncertainty principle in initial state, quickly lead to the sort of chaos this video illustrates.  IE -- macro scale chaos phenomena lead to quantum stochasm bleeding into macro-scale stochasm.
If the importance of a triple pendulum example is not fully obvious to everyone -- basically all physical structures have vibratory modes -- basically analogous to a pendulum cycle.  And these modes overlay on each other, potentially changing the location of a surface point at any given time, very similar to how the point of the three pendulums depends on the phase of all three.  These vibrations are of much smaller amplitude than a pendulum swing, but the surface location of all solids is subject to this sort of vibration-dependent chaos.  Any IMPACT between two macro sized objects, therefore, will not be at a predictable instant in time, but will be stochastic-- based on the instantaneous location of each surface.  This leads to some intrinsic variability of impact time, and also resulting impact directions between the two objects.
One of the ways thinkers have tried to reconcile chaos to causation, is to accept that one form of causation can be a bounded envelope, such as the range of motion of a vibrating solid, or a triple pendulum -- plus a statistical probability within that envelope.  This approach also works for QM.
While the founders of quantum theory embraced stochasm, not all their peers have done so.  And while stochasm has been one of the main motivators behind attempts to reinterpret quantum theory, it has not been the only philosophical concern that has motivated their peers to try to recast Quantum Mechanics.    The efforts to recast quantum theory have lead to a proliferation of "interpretations".  The original purely stochastic understanding of quantum mechanics remains the dominant one (it is now called the Coopenhagen Interpretation), but the stochasm of QM has at least been debated among physicists.
The two key legs of stochasm have been Heisenberg's Uncertainty Principle, which notes that one cannot actually discover the product of pairs of terms to less than a certain uncertainty content.  The clearest product to illustrate this is time and momentum.  https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/Heisenberg%27s_Uncertainty_Principle If we cannot know either the initial or final states of a system precisely, that brings not just predictability into question, but Heisenberg thought the entire concept of causation was now suspect.
The other leg has been quantum mechanics -- that the behavior of elementary particles is like waves, that decompose into particles for interaction purposes at stochastic locations within the wave-field.  One of the clearer aspects of quantum mechanics, is that the decay of a single radioactive atom -- will not occur at a predictable time but will occur randomly based on its "half-life".  The developers of QM recognized that this is a violation of not just determinism, but also of normal understandings of causation.
One of the other features of QM is that it also appears to violate either relativity, or the mind-independent realism of our world.  Bell's Inequality spelled out a test case between local realism and QM's predictions and the tests to date have demonstrated that QM's violations of local realism are confirmed as how our world works: https://www.quantiki.org/wiki/bells-theorem
Einstein was one of the major leaders in the effort to challenge the stochastic nature of QM, but not only that, the local and unreal aspects of it as well.  He postulated a set of alternative interpretations of QM observations, which failed test after test.  His final effort was the concept if intrinsically hidden variables, unable to ever be observed. He got grief over this, as he seemed to be violating one of the key aspects of science-- refutability of one's theories. But Einstein, as a good scientist, pushed for ways to test his "interpretations" vs Copenhagen.  Note if tests can distinguish between them, alternative "interpretations" are actually alternative theories.  The Bell's Inequality tests were inspired by an effort to make this final intrinsically hidden variable theory testable, and it too failed those tests.
Other "interpretations" try to preserve locality, by embracing "unreality", IE that the observer is inseparable from quantum events. A list of many of these interpretations is here;  https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics  Most of the advocates of these alternative interpretations have not been as aggressive as Einstein was in trying to derive test cases between them and Copenhagen, hence most have not been as clearly recognized as actually competing theories.
The only two alternatives from this list with significant support from physicists today are Bohm-DeBroglie, and Everett's Many Worlds.  Bohm's is a hidden variable model, with global rather than local hidden variables.  What that means is that every event is influenced by every other object in the universe, regardless of distance, and regardless of speed of light limits.  Bohm sacrificed compatibility with General Relativity, for the comfort of a deterministic model.  It has now been fairly widely recognized that Bohm's theory is different from QM, and it is often now described as Bohmian Mechanics.  The results of test cases to date, have been strongly trending against Bohm and in favor of Copenhagen; http://settheory.net/Bohm https://www.physicsforums.com/threads/back-pedaling-on-bohm.905194/.  Bohm -- has not been widely considered refuted yet -- but these observations and test cases have drastically dampened enthusiasm for Bohm's theory.
Many Worlds postulates that for every quantum event, all possible outcomes occur, and the universe splits to create alternate non-interacting universes for each possible outcome.  Many Worlds is claimed to be a "deterministic" theory per the Wiki page, and many advocates.  But this does not appear to be the case.  For any observer, there will only be one outcome to any event, and that outcome is not deterministic, but stochastic.  Postulating that other observers exist, and that all possible outcomes are observed between the theoretical collection of all of them -- still leaves each of them as a single observer, experiencing a stochastic event.  per the standard for determinism set for classical physics -- LaPlace's Demon could neither know the current state of the universe (it would still be limited by Heisenberg Uncertainty Principle), nor could it predict the outcome of any measurement (echoing Earman's language relative to classical physics, "there is not a singular solution").  "All of the Above" is not really determinism.  Plus -- postulating excess universes that are undetectable in principle -- is a violation of science basics, for which Einstein received some justified grief.
Additionally, Many Worlds, from a pragmatic causal point of view-- explicitly abandons causation, and cannot even adopt the envelope/probability approach that plausibly can encompass chaos events.  This is because probability between the worlds becomes a nonsense concept -- all of them exist, and there is no "bandwidth" feature to these different universes to the theory than can distinguish "frequency".   Putting this in personal terms, I could in the next 20 minutes, complete this entry, and post it, abandon the project and play video games instead, or walk next door and murder the neighbor family. All are possible, none are any more "caused than the other, and each occur in SOME world per MW "interpretation".  such a radical elimination of the concept of causation, is not what most determinists are looking for, and the popularity of the MW interpretation is likely due to its non-physics adherents not understanding how it destroys any coherence to causation.
At any rate, Bohm appears to be heading down the same path of refutation that Einstein's hidden variable theories followed, and MW is not really a deterministic model. Quantum mechanics is reasonably understood as refuting determinism in physics.  This combined with both the indeterminism in classical physics, and the intrinsic unpredictability of chaos phenomenon (and actual indeterminism once one includes Heisenberg's uncertainty), leads to a definitive answer -- physics is not determined.
Comment: "physics is not deterministic" - **that's not what the answers to [a similar question on the physics site](https://physics.stackexchange.com/questions/63811/is-the-universe-fundamentally-deterministic) are saying**. I'm not really inclined to dig into all the physics, and this definitely isn't the appropriate platform for this. But at face value, when it comes to a question about physics, and lacking proper expert peer review, I'd trust the correctness of the multiple answers with dozens on upvotes on a physics site (saying we don't know) above an answer on a philosophy site with 3 upvotes.
Comment: @Frank The argument that I answered postulates that physics at least in principle predicts a unique solution to a unique prior state.  This is the claim of determinism. I cited the reasons this is not true for physics. We can with confidence know that physics is not deterministic — it does not satisfy the assumptions needed to make deterministic conclusions about our universe.  That physics is not a single coherent theory is ALSO true, and that people make other invalid general inferences about physics is true too.  But those are not relevant to this question or answer.
Comment: @Frank -- on the contrary it is a very clear and valid conclusion one may draw from the set of test cases that "physics is deterministic" fails.  It really is possible to reason about and draw useful conclusions from complex aspects of our world, and no, such reasoning and conclusions are not "meaningless".
Comment: @Frank -- regularities =/= determinism.  Strawmanning and false dichotomies are basic reasoning errors.
Comment: @Frank -- anything which is only "quite determined" and not "absolutely determined" is not actually determined.  Gravity in classical physics is not determined -- the "multiple solutions" noted in the answer apply to cases of unstable equilibria -- so how these cases will proceed is stochastic, not determined -- and Heisenberg and chaos theory will drive the stochastics of the breaking of the unstable equilibrium.  And if/when gravity is integrated into quantum mechanics, it too will have stochastics at its base.
Comment: Not sure what you mean by "physics is not determined". It's actually more subtle. For example, in QM, the classical limit can be recovered for expected values of coherent states (see https://en.wikipedia.org/wiki/Classical_limit, and Zwiebach, Mastering QM, Chapter 17, for example). There is loss of determinism in some experiments, but after all, the trajectory of cannon balls is still very deterministic.
Comment: @Frank -- that indeterministic physics can generally be approximated by a deterministic model is different from physics being deterministic.
Comment: I'm just pointing out that grand claims such as "physics is deterministic" or "physics is not deterministic" are not meaningful when you really look at it. It is more complicated. "Physics" has many branches. Physics deals with approximations all the time. Some theories of physics overlap with others in certain regimes. Some laws are valid only in a certain regime. You just can't make a claim such "physics is/is not deterministic", no matter how fascinating "the loss of determinism, hidden variables, spooky actions at a distance, etc etc" trigger the fantasies of the layman.
Comment: there is more! If you want to make physics say more than what it really says, you can also fantasize on "quantum teleportation", "entanglement", "uncertainty", "energy-time uncertainty", "time evolution operator", "no-cloning property" ... I'm just going off Zwiebach's QM textbook chapter titles - sure to trigger grand generalizations about the fate of the universe, consciousness, free will, the existence of god, not forgetting hours and hours of science-fiction... But physics makes no statement whatsoever about those grand generalizations.
Comment: but this is not how it works in reality. You can't stop at the layman sound bite "physics is not deterministic", however appealing it seems. Classical mechanics is very deterministic in its range of applicability. "Physics is not deterministic" is a meaningless simplification of what actually happens in "physics".
Comment: since physics is not deterministic, I suggest the following experiment: step from a ledge 100 times, and count how many times gravity is not going to pull you down towards earth. Surely, since physics is not deterministic, there will be some cases where you will just go up rather than down?
Comment: Not a strawman, I'm merely pointing out that gravity at the macroscopic level is quite deterministic on the following meaning of "deterministic": the same prior state of an object at time t predictably and reliably leads to another state at time t+1. So "physics is not deterministic" feels like an undue generalization to me. By the way, there are multiple possible ways to define "determinism", which makes the claim "physics is not deterministic" even more suspicious.
Answer: So, there are three models of quantum mechanics which maintain determinism: non-local hidden variables; superdeterminism; and determinism across many worlds. These are constrained by the Bell Inequality having being violated.
This is because, sensitivity to unitial conditions, the underlying characterustic of chaotic systems (such as whenever more than two oscillators interact), mean any quantum measurement could in principle be enough for a different outcome from otherwise the same initial conditions.
So. Non-local hidden variables are problematic because they violate Occam's forbidding of multiplying entities, a hidden invisible layer of order is required that seems to be unfalsifiable. Superdeterminism is problematic because from inside the system it would be unpredictable, and the implication has to be, for it to be verfiable, that you could step outside the system to view how it is deterministic, violating that determinism - so again it's unfalsifiable. Many world's (also called relative state interpretatiin) is probably the most popular interpretation of quantum mechanics among physicists, it allocates the randomness to which branch of the system we find ourselves in, and the system evolves down all posdible branches in a higher dimensional Hilbert space. It seems possible there is a fundamental limit to the information per unit of space-time, linked to the Planck length & time, which would help explain black hole behaviour. This would seem to place a constraint on the total number of paths a system could go in, but it's an extremely high number.
There is another option. The interpretations of quantum mechanics hinge on observer and observed, many worlds pictures states as relative, one quantum system observing another. The It From Bit doctrine suggests matter is not fundamental, information is. Emergent properties are self-stabilising systems, like life, and minds. I see these pieces as pointing towards a materialst-physicalist pan psychism, that the universe is on a deep level the result of it's own enquiry into itself, exploiting it's own lack of knowledge about itself to determine how to be, by amplifying those indeterminisms in a way that is self stabilising, like a mind. Like Indra's Net. Just a hunch though really.
I was talking about free will recently, and this may make the idea clearer: Free will from a self-conscious being's perspective; unfree will from the universe's perspective. Only, the universe has no perspective, there is in fact only intersubjectivity, no universal transcendental perspective, only relative local ones. Mind then wouod be the fundamental strata of being, and world and physicality arises from that, but is prevented from being arbitrary and purely subjective by arising with and in a shared intersubjective mental space. Arising at the 'door' (sense-gate) between mind and world. It's a logical continuation of the private language argument's intersubjectivity. To boil it down, we have freewill for the same reason we have identity, 'I' ness, or that fiat currency exists: we have a convention and act as if it's real, creating a world in which it is. You can say money isn't real, and I point to observables in the world which say it is - but the way in which it's real is not like atoms, it's like the category 'things you can sit on'. Relative, but social. See also peer-to-peer simulation hypothesis
Answer: In a deterministic universe nothing ever happens at random nor at will. A deterministic universe could not be intentionally created nor could it have evolved unintentionally through random fluctuations or probabilistic indeterminacy.
A deterministic universe is a logical impossibility. Determinism precludes both methods for determining the contents of a universe.
Comment: It doesn't matter that it would be a logical impossibility, because after all, we created "logic". The universe didn't ask for our "logic", and if somehow an observation undermines our human "logic", then the onus is on us to change it. You have to defer to what the universe will tell you, even if it contradicts human "logic".
Comment: @Frank A deterministic universe is not an *observation*. It is a product of human imagination, a demonstration of human capability to imagine illogical things.
Comment: @PerrtiRuismaki - it sounds like we agree then?
Answer: For a similar question on the physics site, the top-voted answer mentions indeterminism, but says the mechanism "is still not well understood". A significantly-upvoted comment says the alleged source of indeterminism is "sweep[ing] things under the rug" and alludes to non-locality. The second answer just says "no one knows". The third answer mentions indeterminism, but also points out that abandoning locality is an alternative. The fourth answer says it is deterministic. Interpret that how you will.
There are various interpretations of quantum mechanics which vary in terms of whether it is deterministic or stochastic, among other factors, and we don't know what the correct interpretation is.
I don't expect philosophy to produce better answers to this question about physics than ... well, physics, or for laypeople to be able to produce better answers than physicists. Anyone acting otherwise should be treated with significant skepticism.
Philosophical determinism vs measurement determinism
There's also an important distinction between philosophical or physical determinism and measurement determinism. We can perhaps say that the exact path of a falling feather released outside is indeterministic from a measurement perspective, as in we can't predict where it would go, because tiny, functionally-immeasurable differences in air pressure could change the result, and we may model this probabilistically. But it may nonetheless be philosophical or physical deterministic, as in if you could hypothetically release it under the exact same circumstances, it may travel along the exact same path every time.
Now we wouldn't typically describe a falling feather as indeterministic from a measurement perspective, because we understand the underlying mechanisms that would affect its behaviour (even if controlling for all of that may not be practically achievable, except maybe in a vacuum, and quantum effects could factor into it). For quantum mechanics, we don't understand the underlying mechanisms, and the most accurate model we have at this point to describe behaviour is probabilistic, and we may say it's indeterministic from a measurement perspective. This is the core of quantum mechanics.
Where interpretations of quantum mechanics differ is whether it's actually intrinsically deterministic. Some interpretations, including the popular Copenhagen interpretation, propose that quantum mechanics is fundamentally indeterministic, but not all of them do. Quantum informational interpretations, for example, state that "quantum mechanics is said to describe an observer's knowledge of the world, rather than the world itself".
Quantum mechanics is not magic
It's probably also worth pointing out that QM is not magic: it does not suddenly everything possible, even though some people seem to treat it as such. It's commonly referenced by free will proponents, but even being as generous as possible, the probabilistic behaviour of independent atomic particles wouldn't get you anywhere close to anything resembling meaningful human agency, under pretty much any interpretation of quantum mechanics.
Comment: (Downvoted by another answerer who doesn't seem to like me presenting facts and arguments that prove them wrong.)

Deterministic or stochastic universe?


How is age useful for Stack Overflow or Stack Exchange?

Question: Last time I was asked for my age on the web was when I created my email account. How is age helpful in user experience? Why is there an age section?
Comment: @Lix the OP is not under 13 he's just asking what is the benefit of showing user's age..
Comment: @Santosh its not a mandatory field - its optional - ie its for information only
Comment: Related: http://meta.stackexchange.com/questions/61770/how-do-i-use-stack-exchange-if-im-under-13-years-old
Comment: And specifically ["Why is this restriction in place?"](http://meta.stackexchange.com/a/102250/172936)...
Comment: No, I'm asking "Is there any use of showing age on Profile page? How can it help?"
Comment: It is there because your birth date is also supplied... If you remove that from your profile the age will also be hidden - its just information about the user...
Comment: Once again, why is birth date supplied? How can it help in Q&A? Specially in SO.
Comment: did you read the first two links in the comments here?
Answer: It's just another piece of information about you, same way like you can provide your real name (as the nick), your location and free text in the About section.
It does not have any "direct" value by itself, people should not treat someone differently just because he's X years old and not Y years old.
Answer: Maybe some users will trust you more when you are in a specific range of age? It doesn't bother me too much. Probably I would not vote someone for moderator when the age is only 13 ...
Personally I don't want to tell the world my age. On the downside, I will never get the "Autobiographer" badge.
Comment: I could not be proud of that badge ...
Comment: You could always provide *a* birth date (it doesn't *have* to be yours), get the badge and then remove the information ;)
Comment: I wasn't being *totally* serious there.
Comment: 13... I wonder who should run for moderator
Answer: The field is optional. If you don't want to make your age public, then you don't have to fill it in.
One's age is simply a logical thing to include in a personal profile, along with one's name, location, and website. As you observe yourself in the question, lots of other services ask you to provide your age, including email providers.
Ageism is, like other "-isms", strongly discouraged.


Reason behind Inertia

Question: Has any physicist work on the reason behind Inertia?
Why do we have inertia only during acceleration?
No inertia during constant velocity.
Comment: This eludes to the question of what is momentum.
Answer: You have inertia all the time. Physics has advanced since Newton.
Now we know that an object has energy and momentum and that they combine together to give a 4d energy-momentum vector with four components. And mass is the length of that vector.
When objects have relative velocities that are small compared to the speed of light, those vectors point in almost the same direction so the sum of the lengths is really close to the length of the sum. And that's why two bowling balls have a mass that is really close to the sum of the mass of each.
We've also learned that mass isn't the source of gravity, that the stress-energy tensor is and that empty space itself can be curved in its own, even far from stress-energy.
We've also learned that you don't have to have mass to be affected by gravity.
And we learned that forces are really about exchanges of energy and momentum and so you can experience a force by exchanging energy and momentum with a field, even a field with zero mass (and that the squared lengths of the energy momentum can be zero even when the vector is nonzero).
So we've learned a lot.
Comment: @Anni You can read it everywhere. Light doesn't have mass and yet it's trapped by a black hole. So it's probably something you've heard before, I'm just making a big deal about the things you need to unlearn. For instance in my two most recent answer (http://physics.stackexchange.com/a/241765) I point out that you think things fall because of gravity but really the inertial frames are the freefall frames and the earth is pushing you upwards when you stand on the surface because the pressure of the ground on your feet exerts a force on you. So light effectively "falls" too.
Comment: 'We've also learned that you don't have to have mass to be affected by gravity.' what???? where i should read about it?
Comment: You dis not answer my question in a direct manner. Shall I read energy stress tensors?
Why does mass not resist velocity but only acceleration? I think no physicist could explain it so far.
Comment: @AhmetGazi You asked why inertia only exists sometimes. The answer is that inertia doesn't only hold sometimes. But answers aren't allowed to be that short. But that's the 100% answer to your question. Whatever speed you go, there is a frame that sees you at rest in which case, what velocity is there to resist?
Answer: Look inertia is present all the time. But you can feel it only when your state of rest or motion is changed because of acceleration. This doesn't mean that you have inertia only during acceleration.
Inertia is just a property due to which we remain at the same place as mentioned by Timaeus .
When you are standing on a bus and the bus accelerates then your feet accelerates with the bus due to friction but there is no force on your upper part and so it remains at its position ( due to inertia) . This is the reason why you feel inertia while accelerating.

Reason behind Inertia


Are locally compact Hausdorff spaces with the homeomorphic one-point compactification necessarily homeomorphic themselves?

Question: When practicing old qualifying exam problems, I had trouble with this one. Thanks for any help!
Is it true that if the $1$-point compactifications of two locally compact Hausdorff spaces
$X$, $Y$ are homeomorphic, then $X$ and $Y$ are necessarily homeomorphic? Give a proof
or counterexample, as appropriate.
Comment: Do you have a guess? There are some very elementary examples that will tell you the answer. Try to think of familiar compact spaces and remove a point. Do you always get the same space? You can then turn this into an answer.
Answer: Always think about the simplest cases first! What possible one point comp. could give rise to, say, [0,1]?
Comment: Just because I'll be studying for Quals myself soon enough, could one take as examples $X=[0,\frac{1}{2})\cup(\frac{1}{2},1]$ and $Y=[0,1)$? It seems the one-point compactifications will both give rise to something homeomorphic to $[0,1]$, while $X$ and $Y$ are not homeomorphic as they don't even have the same number of components.
Comment: Yes, that's the example I was thinking of! The key idea in constructing this example is that whilst restrictions of homeomorphisms are homeomorphisms, one needs "the one point that is added to be the same in each case". Trying to violate this gives rise to lots of similar examples.
Answer: Sharkos's answer tells the story simply and eloquently. I think it's worth noting that the converse does hold. That is, if $X$ and $Y$ are homeomorphic, then their respective one-point compactifications $\alpha X$ and $\alpha Y$ will be homeomorphic as well. Indeed, let $f:X\to Y$ be a homeomorphism and let $g:Y\hookrightarrow\alpha Y$ the canonical inclusion. Show that $g\circ f:X\to\alpha Y$ is continuous and injective. Since $X$ is dense (when canonically included) in $\alpha X,$ then there is a unique continuous function $h:\alpha X\to\alpha Y$ whose restriction to $X$ is $g\circ f$. Show that $h$ is a homeomorphism. You may need to consider separately the case where $X$ and $Y$ are compact Hausdorff and the case where they are not (one is trivial).
Comment: It seems to me that this is just true because the Alexandroff construction is indeed *topological*: i.e., makes use of only homeomorphism-invariant properties of the topological space.
Comment: True enough, Pete. The proof I outlined is very brief, for just that reason.
Comment: I just remembered that I wrote the wikipedia article http://en.wikipedia.org/wiki/Alexandroff_extension.  Take a look at the last sentence!
Comment: Interesting! I've not had much experience with category theory or functors, but that seems an apt perspective.


same article with different categories

Question: Can we access same articles in different categories? I want to show one article in different categories using Category blog layout. Please advise how.
Comment: Please look at this question- http://joomla.stackexchange.com/questions/8858/how-to-categorize-an-article-under-many-categorizes
Answer: Joomla does not allow an article to be placed in multiple categories.
But still we can alter the category blog layout to display the desired content.
This can be achieved using template overriding.
You need to override category blog layout template and place your code which will check whether the current category is the same in which you want to display that article then fetch the article data and render its content.
This is some sort of a patch you can say, so in case you need to achieve this scenario for large set of articles and categories then you need to write a little generalized code.
Answer: The easiest way is to copy the article and save it to the desired category: Edit article, than save as copy, choose different category...save.
And there is another, different option. You can label the requestet article as "main" and display only main articles of the same or different categorys under one menu-item or something like that, module and so on...
Comment: Nooo! What a content maintenance nightmare.
Comment: Yes it is. And imagine you have a multilanguage Website. It´s a mess...but the filter option at the backend is most helpull.

same article with different categories


Play youtube video in slider and pause slider

Question: I am making my custom jQuery slider. I want to pause slider while youtube video is playing. So I need a reference or any help so I can complete my slider.
Comment: What is your question? What kind of reference are you looking for? What have you done so far, and do you have any example code? Right now you're not really asking a question, but just saying that you need a reference.
Answer: With the YouTube API you can stop your slider when the video is on playing mode. Try to play a little bit with this > https://developers.google.com/youtube/youtube_player_demo?hl=fr and here you can find a great example of what you need > https://code.google.com/apis/ajax/playground/?exp=youtube#chromeless_player
You can get the current event of your video and then pause/stop your slider.
Let me know if you need more details about this issue.
Comment: Hi Ussama thnx for your help. I can pause slideshow when video is playing but can not pause slideshow when video is getting load first-time after click on play button.Currently It moves to next slide and it pause slideshow when video is ready to play.
Comment: So you just have to pause the slideshow when you click on the play button using a simple `.click()` mouse event.

And you're welcome.
Answer: I suppose you're using an embedded player using the iframe api:
https://developers.google.com/youtube/iframe_api_reference
If not, I strongly suggest you do so. It'll allow you to listen to the player's state change event and execute a function when it starts playing.
Taking the page's example, in the "Get started" chapter, I'd suggest doing something like this:
<code>var player;
function onYouTubeIframeAPIReady() {
    player = new YT.Player('player', {
        height: '390',
        width: '640',
        videoId: 'M7lc1UVf-VE',
        events: {
            'onReady': onPlayerReady,
            'onStateChange': onPlayerStateChange
        }
    });
}

function onPlayerStateChange(event) {
    if (event.data == YT.PlayerState.PLAYING) {
        // Pause your slideshow
    }
}
</code>
Modify the parameters for the player to your liking and write your own code to stop the slideshow in the onPlayerStateChange function. There are other states that you might want to check in that same function, described in the "Events" chapter, such as the paused or ended states.


Alternative chalk board materials

Question: For the sake of context, this is a fantasy setting where this character has no access to magic and lives in a small village. He would like to write a book and since wiriting materials are a little expensive he would like to plan out pages in inexpensive chalk first. My thought is to use a series of unglazed clay or ceramic tiles since clay is plentiful. Does this make sense or would it be too much of a pain to use?
Comment: Why do you need an alternative material for the board? What's wrong with slate, or a piece of painted wood?
Comment: if you want cheap bark or wood and charcoal which are as close to free as you can get. you can get chunks of charcoal out of any cooking fire.
Comment: @ChristopherJamesHuff you don't even need to paint the wood, just a dark wood rubbed smooth with sand was common for a long time. Medieval masons used wooden boards to do the the geometry for cutting windows and other precise stone shapes
Comment: @John yeah, I only suggested painted wood because that's a more modern chalkboard material, but plain wood will work too, you just need to be a little more selective about the type of wood. Which really just shows that the question needs clarification: alternative to what, specifically? Are we looking for historical materials used before modern industrially-produced chalkboards? Alternatives *to* those materials, something that *wasn't* widely used in recorded history?
Comment: @john, and Christopher thanks guys, as you can see I was having trouble finding the steps prior to slate chalk boards and clearly over thought it. I guess the answer is alternative to a missing link that you have given great options for
Answer: The ancient erasable and reusable low-tech scratchpad is a wax tablet. Wax tablets were used for a thousand years in the classical world, and they have the advantage of being hand-portable, unlike a blackboard.

Left, modern reconstruction of a Roman wax tablet diptych. One wrote on them with the sharp end of the stylus; corrections and erasures were made by tamping the wax with the blunt end of the stylus; for a full reset the wax was melted. Photograph by Toilet, available on Wikimedia under the GNU Free Documentation License, Version 1.2 or any later version. Right, a 19th century slate tablet for use by school pupils; one wrote on them with a chalk pencil, and they were erased with a damp sponge. Photograph by GodeNehler, available on Wikimedia under the Creative Commons Attribution-Share Alike 4.0 International license.
Blackboards or chalkboards are a modern invention, late 18th or early 19th century. The original blackboards were made of natural slate stone, sort-of oversized versions of the slate tablets used by school pupils since the 1500s or so.)
The Greco-Roman wax tablets and the early modern slate tablets have left their traces in the fixed phrases tabula rasa (literally, scraped tablet), (to start from a) clean slate, and to wipe the slate clean.
Answer: A piece of soapstone will write on a slab of slate just like chalk on a chalkboard without the need of manufacturing or processing of the materials. Sourcing these materials should be easy enough to justify and use of them is realistic and perfectly reasonable.
Answer: Birch bark, provided that you have those trees around, is rather cheap as a writing material:

Birch bark or birchbark is the bark of several Eurasian and North American birch trees of the genus Betula.
The strong and water-resistant cardboard-like bark can be easily cut, bent, and sewn, which has made it a valuable building, crafting, and writing material, since pre-historic times. Today, birch bark remains a popular type of wood for various handicrafts and arts.
Removing birch bark from live trees is harmful to tree health and should be avoided. Instead, it can be removed fairly easily from the trunk or branches of dead wood, by cutting a slit lengthwise through the bark and pulling or prying it away from the wood. The best time for collection is spring or early summer, as the bark is of better quality and most easily removed.
To prevent it from rolling up during storage, the bark should be spread open and kept pressed flat.

It was commonly used before the invention of paper

Birch bark manuscripts are documents written on pieces of the inner layer of birch bark, which was commonly used for writing before the advent of mass production of paper. Evidence of birch bark for writing goes back many centuries and in various cultures. The oldest such manuscripts are the numerous Gandhāran Buddhist texts from approximately the 1st century CE, from what is now Afghanistan.

It has also the advantage of taking less space than writing on pottery or tablets, because it's thinner.
Answer: Consider the metalpoint / https://en.wikipedia.org/wiki/Silverpoint technique. The wikipedia page gives a good historical account you can use for inspiration
Several folk have already mentioned bark as an erasable substrate.
Paper covered in wax works as well, and is an upgrade. And access to graphite works event better
You could have a story line where the writer gradually upgrades materials - maybe using fishbone + bark at first, then getting access to metal pointer, finding chalk and/or graphite, with paper upgrading to wax on bark, then wax on hemp or other rough fibre, then paper etc...
Comment: Silverpoint styli are made with silver; I doubt that's a cheaper alternative to "writing materials".
Comment: The common name for the technique is based on the silver styli, but that's just a historical oddity. I recommend reading the wikipedia page. It gives a solid history for the writing utensil and materials used (including eg. copper, bone, iron, etc...), suggesting how one might progress through them
Answer: Charcoal on panel.
Coat the panel with traditional gesso, a mixture of skin glue and chalk (or another whitening agent). The result can be a perfectly smooth and beautifully white surface, and you can easily wipe off the charcoal and start over. When the surface gets too grey, you can wipe it clean with a little water, or simply apply a new layer of gesso.
Answer: If you have pottery (very likely in medieval settings), then the ostraca are cheap (literally broken trash), plentiful and durable. And they were good enough for ancient Greeks as well.
Alternately, in more Chinese-like settings, where bamboo is abundant, you can use bamboo slips.

Alternative chalk board materials


How can I run and stop IISExpress from jake

Question: I'm able to kick off IIS express to run my mvc 3 app with the following coffeescript line:
iisex = jake.createExec(['iisexpress /path:' + process.cwd() + ' /port:9090 /systray:false'], {printStdout: true})
#listening code here
iisex.run()

I then run some jasmine tests using
ex = jake.createExec(['phantomjs run_jasmine_test.coffee http://localhost:9090/app/applebees_testrunner.html'], {printStdout: true});

Test pass and now I want to kill IISExpress.
The problem is that now I have a long running process and the process wants me to 'press q' to stop the server.  Is there a way to send a q to the running process so that the server will stop?
Answer: Perhaps this helps.  Is there a way for you to run the following command (needs cmd line opened with admin rights - to do this manually).
iisreset /stop


Finding value of x ? Rate of change

Question: A cube of ice is melting at a constant rate . The initial volume of the ice cube is $20cm^3$ and volume after $5$ mins is $15cm^3$. Find the rate at which the length of the cube is decreasing at the time $t=12$mins
My attempt
Let length of the cube = $x$ cm
$\frac{dV}{dt} =( \frac{dV}{dx} )(\frac{dx}{dt})$
$\frac{dV}{dt} = \frac{20-15}{5} = 1cm^3/min$
right now , I understand I need to find
$  \frac{dV}{dx} $
I must form an equation of with x
Using ratios ....
$V= (x)^3 $
$ \frac{dV}{dx} = 3x^2 $
Now I'm struggling to find the value of $x$ to substitute into.
I was told
$x^3 = 20 - 12(1) $
But I don't understand the above equation at all .
Any help would be appreciated ! Thanks!
Answer: hint
$$V (t)=(x (t))^3$$
$$\frac {dV}{dt}=3x^2 (t)\frac {dx}{dt} $$
$$\implies \frac {dx}{dt}=\frac {dV}{dt}\frac {1}{3 (V (t))^\frac {2}{3}} $$
At $t=12 \; min $,
$V (t)=15  \;cm^3$
$\frac {dV}{dt}=\frac {15-20}{12} \;cm^3/min $

Finding value of x ? Rate of change


Is it possible to convert 19.5V 3.33A to 12V 5.5A?

Question: I have a laptop charger which has 19.5 V 3.33 A output. I want to use it for raspberry, which needs 5V and 2.5A and for monitor which needs 12V 3A. Is that charger strong enough to run the whole system? Is it possible to convert 19.5V 3.33A with a buck step down to 12V 5.5A which will be connected to monitor and then use an another step down to 5V 2.5A to feed the raspberry, or I have wrong idea about everything? Sorry I do not know much about electrical engineering.
Thanks!
Comment: People who know nothing about EE nor basic Grade X11 physics should stick to buying solutions.
Comment: Tibor - Hi, "*I have a laptop charger which has 19.5 V 3.33 A output*" Just a warning that some laptop chargers sold on Ebay, Amazon, AliExpress etc. which *claim* to have a quoted current rating, *don't really have that rating* and can have poor quality or even unsafe internal construction.
Comment: A rpi doesn't need 2.5 Amps tho.
Comment: This is a bad idea.  You'd be better off using power supplies designed for each output, or for suitable combined 5v/12v output.
Comment: Welcome to EE.SE! Keep in mind that *"Is it possible ...?"* is a yes/no question. In this case, the answer is "Yes". If you're asking us to design it for you, that would be too broad. You would need to specify something about the level of performance you expect as well as what constraints you have on the implementation. What is your specific question?
Answer: The answer to your header question is NO!
Input 19.5x3.33 = 64.935 Watts.
Output 12x5.5 = 66 Watts.
So your new output power is higher then your input power which is against the law of conservation of energy.

But according to your question details your equipment requires only 48.5 Watts.
That is do-able but only if your buck step down converter (or converters) has/have at least 75% efficiency.
But as Chris Stratton already said: it is better to use supplies which are dedicated for the circuits. You will be spending time and effort on something special, whilst there are cheap, ready made solutions. The idiom "penny wise, pound foolish" comes to mind.
Comment: sounds like an interesting project Tibor is trying, and he'll probably learn a lot.  "it is better to use supplies which are dedicated for the circuits" _assumes he isn't doing this to "just" learn more for fun_
Comment: there are cheap ready made switcher modules on every online marketplace. so long as you de-rate them 30% or so on current they work well.
Answer: Yes, it is possible
power of laptop charger is = 19.5 * 3.33 = 65 Watts
your loads power:

raspberry pi = 5*2.5 = 12.5 watts

Display = 12 * 3 = 36 watts
total power = 48.5 watts

Total power < power of charger,
you can use it. it will work
Comment: Conversation of energy is not violated, sure.  But actually implementing it will require some effort and will probably not turn out economical.
Comment: Uh, 12v at 5.5a is 66 watts.
Comment: DC-DC converters are pretty cheap. If you can convert 19.5 V to 12 V with 80% efficiency, and then 12 V to 5 V with 80% efficiency, the numbers work out almost exactly. You get 4.33A @ 12V, the monitor takes 3A, and the remaining 1.33A converts to 5V @ 2.55A. Of course, if you convert directly from 19.5V to 5V, you get almost 3.2A to play with.
Comment: @HotLicks: Uh, Satish corrected the mistake in the question of thinking that the input to the RPi stepdown converter would be the same current as the output.


DataFolder not found in the UI

Question:
I created a DataFolder of ContentType dataextension through SOAP API.
It was successfully created and I was also able to create a Data Extension with the ID of the data folder created in step 1
I am able to normal operations on the data extension.

However I am not able to see the data extension or the folder in the Marketing Cloud UI. If I create a data extension without mentioning CategoryID I am able to see the data extension in the UI at root level.
Where can I find this data extension in the UI?
Answer: You have to provide parent folder ID.
"datafolder.ParentFolder.ID"
You can check those in UI by "right clicking" a folder and inspecting one (Web-dev tools in Google Chrome for instance)

DataFolder not found in the UI


How to add facebook friends searchbar in website

Question: I am learning facebook php and javascript sdk. I am trying to create a facebook search friend bar in my app where user types friends name and as user types, the searchbar should display most appropriate result while user is typing. Similar to what facebook search bar does. Is there a social plugin or any other tool available to acieve this task? To achieve this, I tried facebook comments plugin with user_friends permission. When user writes any friends name followed by @ sign on comments field, facebook gives most appropriate result. But I dont know how to get what user wrote on comments. Any pointers will be helpful.
Answer: FB introduced API versoining. If you are going to create new app it will use version  v2 and you will not get full friends list from me/friends.
/me/friends returns the user's friends who are also using your app
In v2.0, the friends API endpoint returns the list of a person's friends who are also using your app. In v1.0, the response included all of a person's friends.There are two key use cases where apps need access to non-app friends: tagging and inviting. In v2.0, we've added the Taggable Friends API and the Invitable Friends API to support these flows.After a person has logged in with v2.0 of Facebook Login, calling /v1.0/me/friends and/v2.0/me/friends` will both result in the v2.0 behaviour - both calls will return the set of the person's friends who also use the app.
Read this documentation
https://developers.facebook.com/docs/apps/upgrading
Answer: Either you can create this by yourself (not too much of complex). You have access to the friendlist, so you can get all the friends with <code>/me/friends</code>. You can store them (their name/info) into a variable in your application and implement search. This will make your facebook api concepts better.
Or there are many friend selectors plugin/codes that you can integrate in your application. But you'll have to modify them accordingly since you dont want to show a pre-populated list of friends instead you want to implement search.
I've used mbrevoort's multi-friend selector in my applications.
But if you just want to implement search, implementing on your own would be really easy and less complicated!


SSH when to use public key and password?

Question: I think I understand the difference between Public Key authentication and Password. But how do I decide which one to use and which one is most secure in what situation? Can anybody give me some real life example about when to choose public key and when to choose password?
Comment: Here you can find the answer: http://lwn.net/Articles/369703/
Comment: **Use public key:** *any time you can.* **Use password:** *when you can't use public key.*
Answer:
But how do I decide which one to use and which one is most secure in what situation?

A public key is probably always more secure than a password, as long as the corresponding private key has a password.   This way, even if someone acquires the private key, it's still not usable unless they also have the password, whereas with a password, that's all that's needed.
However, brute forcing a password for a stolen key is probably easier than brute forcing a password for an ssh login, since the later will be slower and obvious -- the server will note the repeated failures and can restrict and report the attacker's IP.  A 10 character password using Base64 characters has 64^10 = 1152921504606846976 possibilities, so it may be feasible for a clever person to crack this, if they can try it with their own equipment on a copy of the key.
Of course, you can't force users to password protect their private keys (unless you issue them).  But you can't force people to be careful with passwords generally, so a password alone doesn't really solve the "irresponsible user" problem.

Can anybody give me some real life example about when to choose public key and when to choose password?

Some people find keys a hassle because you need to store them.  Using a password login is its own hassle, though, if you frequently log in and out, since you must re-type the password each time.
Comment: There is some additionnal fact: If your key gets stolen, then generate a new pair of keys ASAP and make sure that the other key wil be invalid.
Comment: Always thought you could remove password protection from private keys even if issued by a third party with a password. Cannot image how to prevent one from doing so.
Comment: @Zelda : Removing the password would require the password, since the key is encrypted with that password.  Without it, you can't decrypt the key...but I think you mean in the case of issuing keys to users?  Good point.  I'm not keen on the idea anyway.
Comment: @BonsiScott How is that different from if someone figures out your password? You have to know in either case, or it becomes a moot point. Of course good security hygiene would be to change authentication credentials on a regular schedule anyway, but that goes for passwords as well as keys.
Comment: Someone who steals your key (or your password) is unlikely to tell you about it anyway, lol.
Comment: I also want to add that root authentication should be avoided at all cost directly througt the SSH deamon and should allow only to use sudo with a regular user
Answer: Which to use is rather simple.
Key based authentication is generally better as goldilocks has stated. But it effectively binds a user on machine 1 to a specific user on machine 2. Therefore it can be a giant pain in the back side if you need an unknown number of users or unknown number of machines to login.
A good example of when to use passwords would be a server in which it's mission critical to be able to access no matter where you are or what kind of device your using. So when you need access to that server you can get it, via cell phone, toaster oven, friends computer, public computer, or other place that you don't want to permanently "grant access" to.
That said, that server would obviously be a security weak point. Most people and circumstances should use keys. Passwords do have their uses though.
Comment: I disagree, but perhaps I was not clear. A key is a MACHINE + user to MACHINE + user combo. A password is simply a user to Machine + User combo. So 900,000 different machines to one machine + user, passwords are the way to go. Most of us don't really do that we connect 1 machine + user (coteyr@localhost) to 1 machine + user (someone@someserver). If I wanted to build a system that says no matter what client I (coteyr) want to connect to someone@someserver then my only real option is passwords.
Comment: Your premise about keys binding "user on machine 1 to a specific user on machine 2" in a way that passwords don't is **incorrect**.  You must log in as a specific user, whether that's via key or password does not make any difference.  WRT having "an unknown number of machines to login" to, you can use a different key for each of them if you want (see `man ssh`, the `-i` option), and *your remote user can allow for more than one key* -- which actually makes the key login *more flexible* than the password login, since normal *nix systems only allow for one password per user.


find maximum and minimum for any function

Question: I'm writing an optimization algorithm thats supposed to find the maximum and minimum value of any given function. Whats the fastest numerical approuch to do so?
Comment: Functions in one real variable? Continuous? Is it known that there is only one local maximum in an interval?
Comment: yes continous functions with one real variable and one local maximum
Comment: I think you must specify the question. There are many fast algorithms for special classes of functions, but there is no algorithm that can handle "any given function".
Comment: Are there other restrictions? Saw-tooth functions with domain $
Comment: I have a function f(x). It is continous and differentiable. I don't know how it looks but I can determine y for every x.
Answer: I don't know how this method is called, so IÄll describe it in full:
If $f\colon[a,b]\to\mathbb R$ has only one local maximum in $[a,b]$ one can use a search basesd on the golden ratio $\phi=\frac{\sqrt 5-1}{2}$.
Given $x_0<x_1<x_2<x_3$ with $x_2-x_0=x_3-x_1=\phi(x_3-x_1)$ and the unique local maximum in $[x_0,x_3]$, do as follows:
If $f(x_1)\ge f(x_2)$ replace $(x_0,x_1,x_2,x_3)$ with $(x_0, x_0+x_2-x_1, x_1, x_2)$, otherwise with $(x_1, x_2, x_1+x_3-x_2,x_3)$ and repeat.
Care must be taken if due to rounding errors the correct order of the $x_i$ might be destroyed.
Comment: I found a technique last year from the 1970s called *Brents Method* which uses parabolic interpolation with safeguarding by the golden search. Perhaps that is what you are thinking of?
Answer: It is very helpful to have an estimate for the number and distribution of local maxima, because most methods can only find a local maximum.  Without such knowledge, I would initially partition the interval into a large number of subintervals, and maximize over each one.  Within each subinterval, you could use @Hagen von Eitzen's algorithm, or the bisection method, or Newton's method to find a zero of $f'(x)$.  After maximizing over each interval, take the maximum of the maxima and (hopefully) there you go.  You can't be sure you've got the maximum, because if one of your intervals had two local maxima, you might have found the smaller one.


interrupts to notify events in linux

Question: I want to write a program which notifies when the laptop battery level falls below a certain threshold level. I am using ubuntu 11.04 . Is there a way in which i can generate an interrupt without polling the battery. What system calls in linux are used to achieve this ?
Answer: There is no system call interface to ACPI in Linux... All of the I/O is done using /proc/acpi or /sys/class entries. Easiest implementation would be a polling software, and read the interface periodically (going to sleep if the threshold is not there yet) — this is because typically /proc and /sys files construct the desired information while handling the read(2).

interrupts to notify events in linux


What is the definition of Infinitely Often class in complexity

Question: I was reading a paper and I came across the term $L\notin i.o.Dtime(2^{n^c}/n^c)$. What is the meaning of this?
Answer: $L\in DTIME\left(2^{n^c}/n^c\right)$ if there exists a machine $M$ running in time $O\left(2^{n^c}/n^c\right)$ which correctly decides membership to $L$ for an infinite number of input lengths, i.e. for every $k\in\mathbb{N}$ there exists $n\ge k$ such that $\forall x\in\{0,1\}^n : M(x)=\mathbb{1}_{x\in L}$. You can think of it as having a non trivial special case where we can decide membership to $L$ (where by non trivial I mean an infinite set of inputs, not just very short ones).
Comment: Then what is the difference between normal classes and infinitely often. Why it mentions infinitely often explicitly? Any normal class is generalized for any length input..
Comment: I didn't say all input lengths, consider the language $L=\big\{\langle M\rangle | L(M)=\Sigma^* \lor |\langle M \rangle| \text{ is odd}\big\}$ is infinitely often linear, since I can trivially handle odd length inputs, even though $L$ itself is undecidable.
Comment: Okay got it...Thanks


use of HTTP Proxy using cURL in C

Question: I'm working on this project that uses proxy server and curl in c and i cant find a good tutorial that teaches me how to. Can you please help me?? i need an example code that shows the use of a proxy server to connect to google.com. maybe using the CURLOPT_PROXY option..
Thanks in advance.
Answer: Well all you do is your normal curl retrieval, but just set the proxy server option.
<code>   curl_easy_setopt(handle, CURLOPT_PROXY, "127.0.0.1:96666");
</code>
EDIT
<code>  /* create headers */
  struct curl_slist *headers=NULL;
  headers = curl_slist_append(headers, "Content-Type: text/xml");

  /* pass our list of custom made headers */
  curl_easy_setopt(easyhandle, CURLOPT_HTTPHEADER, headers);
</code>
Comment: thanx.. but what if i needed to add some extra http headers to the request before sending them??

use of HTTP Proxy using cURL in C


Help finding diagnostic software?

Question: Do you guys know if diagnostic software is capable of telling me everything going on in each cylinder?
Comment: To what level of detail? No software is going to tell you everything what's going on in a specific cylinder. You can gather some information, but other things you have to rely on experience.
Comment: I think the question would be okay with one small change but the title needs work. Fred's answer is good.
Answer: Engine control systems on most common vehicles do not have sensors of any type in each cylinder. This means that engine computer does not have the information to pass on to the software you seek. Some info can be deduced from the available sensor data. Misfire is required by regulation to be reported per cylinder, although it is not required in all circumstances and not all OEM's provide accurate misfire data. For example Honda's data is poor at times while Toyota usually gets it correct.
Some individual cylinder mixture data can be deduced under some conditions by the computer from the oxygen sensors on recent engine designs, I know of no OEM that attempts to include this in the output data stream. It would be very helpful if they did.
Some light aircraft have individual cylinder and/or exhaust gas temperature sensors that can be used for indirect fuel mixture estimates. Parts of this system could be adapted for automotive use.

Help finding diagnostic software?


What exactly are crystal planes and how do they reflect x-rays?

Question:
What exactly are crystal planes and how do they reflect x-rays?
Are crystal planes real physical planes or just an abstract concept?
What are these planes made of?
If they are an abstraction, what do the x-rays hit and get reflected by? Individual atoms?
Then where is the concept of a plane coming in?
And why do different crystal structures have different 'active' reflecting planes?
Could someone please clear up the concept of these planes and Bragg's Law for me?
Answer:

In the image above, you can see a series of Bragg planes drawn in the crystal. This is called one "set of planes". Another "set of planes" would be if one would just draw a series of horizontal lines through the atoms. (Of course by lines I mean planes, but they are projected here onto a 2D image).
The planes are those formed by the atoms, so in that sense they are real -- but they are not "mathematical" planes as those stretch to infinity.
These planes are made from the atoms that form the crystal. Different crystals will have different structures and therefore the planes will be different.
X-rays are actually reflected by electrons most strongly. Therefore, what they are actually scattering off of are the core electrons around the nuclei. What is happening is that because of the structure of the crystal, one can make each of the reflected X-rays constructively interfere by hitting the crystal just at the right angle with the right wavelength of X-ray.
The concept of the plane arises when one considers constructive interference as I have described in 4. The atoms effectively form an X-ray diffraction grating (in a reflective geometry as opposed to a transmissive geometry that we are used to).
As you can see from the picture above, there are many different "sets of planes" that one could draw. Depending on the angle of incidence and reflection with respect to the crystal, one can reflect off any of these planes in principle.
The Bragg Law is a constructive interference condition. The path-length difference between planes is $2d\sin\theta$ and this must be equal to an integer number of wavelengths, $n\lambda$, for the X-rays to constructively interfere with one another. Therefore $2d
sin\theta = n\lambda$ is the condition to get "Bragg Scattering".
Answer:
and 2. Crystal planes contain sets of atoms, which occupy identical positions in the primitive cell.
So to say, the planes are made out of atoms (and nothing in between). Or if you want a more quantum mechanical picture, you would have electron orbitals in between, which are responsible for the chemical bonding.
X-rays get scattered by individual atoms. If many atoms act as scattering centers (e.g. a crystal plane or a set of), the scattered spherical waves, originating from the atoms as point sources, become a planar wave again.
This depends on the crystal structure and symmetry.
Wikipedia might help with nice pictures there.


Why did the bountied questions increase so rapidly?

Question: I don't get it, just yesterday, the number of bountied questions on Stack Overflow was about 50, and today, 500! What could have caused this increase?
Comment: This is a support question asking for help - the answer is helpful, not sure what the downvotes are for. This isn't necessarily something that's easy to figure out on your own. Also, if the answer is correct, this isn't no-repro! Please don't vote to close it as such.
Comment: @AnnZen Could it be that once you looked with a filter applied, and another time without that filter?
Comment: Do you mean that the bounty increased, or that the score on the question increased rapidly after a bounty was placed on it?
Comment: @RobertColumbia I think she's referring to the total number of bountied questions on Stack Overflow, which [as of the time of writing](https://stackoverflow.com/?tab=bounties) is 490. I might be wrong, though, and she would need to clarify if/when she migrates this to Meta Stack Overflow.
Comment: @RobertColumbia I mean the number of questions with bounties increased. On stack overflow, not stack overflow meta.
Answer: You had a filter applied, so you saw only part of the questions.
You can see a filter is in use by watching for the orange indicator next to the filter name:

To get back to full list of questions, just go back to homepage, or the full questions list.
Comment: Thanks. I always go to stack overflow with [python] tag.