Does the price of ham equipment normally rise during winter?

Question: Recently licensed technician here, and going straight into my general class, I'm keeping an eye on cheap (sub-$400) HF radios. I keep reading articles that suggest used radios that normally sell for under 350, but I can only find them on Ebay for over 400 right now, and rising, it seems. Is this a seasonal thing, or is this relatively abnormal, like the recent rise in price of firearms and ammo?
Comment: uff, with the current scale of global economic events, I don't think this can be generalized. Like, there's a shortage of plexiglas. A shortage of e-bikes in europe, sportive bikes in general have increased waiting times. You currently can't buy high-end last generation NVidia GPUs, and the current generation isn't yet available. ... I'd chalk this up to "people are at home trying to figure out how to spend their time".
Comment: nah, as Mike said: buy used! Especially now if people are upgrading to more expensive gear, sensible gear will probably stay affordable. Also, before you spend $1000 on HF gear... let me tell you about other expensive hobbies like 70 to 6000 MHz SDRs + separate amplifiers...
Comment: There are many QRP kits for under $350.  Even some SDR transceivers.
Comment: @MarcusMüller Yeah, but that doesn't mean he shouldn't keep looking. And there are ham radio sites that sell used gear, such as qth.com and qrz.com.
Comment: @MarcusMüller Yeah, I guess. The price of stuff in general is increasing. I was just wondering if I should wait until spring since I don't have my general yet anyways... or buy now while you can still get onto HF at all for below $1000...
Comment: Yes, I planned to buy used in the first place. Ideally under $350 (though that's getting harder to find). Anything I should look out for/avoid? I heard that the Kenwood TS-430S has conductive glue issues.
Comment: Well Prices on the regular Market are quiet stable. If you want stuff that is produced by HAMs that are doing this as a Hobby there can be availability issues. (Like Poty Antenna) I made the best deals during the Garage Sale that are organiced once a year by HAM Clubs near by. The good thing is you can get Broken Hardware and there is most likely some one that can fix it.
Answer: This question was asked in the middle of the pandemic, where people were largely isolated from physical social events.  I suspect that as a consequence of this, amateur radio activity increased to replace those missing social events (I know I did that for sure).  Possibly as a consequence of that, demand for amateur radios increased, to the point where even used equipment has become scarce.  Scarcity leads to higher prices.
Additionally, on October 20, shortly after this question was asked, the AKM chip fab factory caught on fire causing a partial building collapse.  This facility made ADC and DAC chips that are the leaders for SDR based radios and digital audio systems including radios, phones, and high end digital audio equipment.  AKM also makes oscillators used in radios.  While there should have been stock of these parts, when news of the fire got out, any available stock immediately disappeared or prices for it skyrocketed.  AKM outsourced some of its ADC/DAC production (but not the oscillators) to other companies including Renesas, which ironically had its own much smaller fire several months later.
Many manufacturers who relied on AKM parts have halted production, making the radio shortage worse.  Some still have their own stock and production may continue at least through July 2022, but will run out before production restarts and backlogs catch up, possibly in late 2022.
References:

https://www.rtl-sdr.com/avoiding-fake-rtl-sdr-blog-v3-clones-2021-supply-chain-updates/
https://www.akm.com/us/en/about-us/news/information/20210122-information/
https://www.converge.com/resources/news/supply-chain-disruption-news-akm-factory-fire/
https://www.reuters.com/technology/renesas-restore-fire-hit-chip-plant-100-capacity-around-mid-june-2021-06-01/


Can Orisa's halt grab a dead Junkrat's grendades?

Question: So in Overwatch can Orisa use her halt to move the grenades a dying Junkrat drops? I realize it would have to be fast and fired in right direction but would such action be possible?
Answer: Halt doesn't affect anything but heroes, so it wouldn't affect grenades either.
Answer: I have to disagree with Zissouu 's answer.

Halt doesn't affect anything but heroes

While I do not know if halt affects Junkrat's grenades, it sure does affact other things than just heroes.
Try shooting the ability in the starting area while waiting to attack. It will destroy destroyable objects and/or pull them in.
So I'm not 100% certain that it won't affect the grenades


Random number generation for gaussian, cauchy and levy

Question: I am conducting my thesis on Evolutionary Algorithm. To perform various type of mutation I have to generate random numbers from Gaussian, Levy, Cauchy distributions. How can I implement this? I need pseudocode or algorithm.
Thanks in advance.
Answer: First of all, do you really need to implement these RNGs at a low level of code?  If you are going to be, e.g., writing C code, you can link to the GNU Scientific Library, which has all three of those distributions and a lot more besides.  Available on both Linux and Windows, and Mac too I'm sure!  Higher level languages like R also have RNGs built in: rnorm for the Gaussian, rlevy (in the rmutil package) for the Levy, and rcauchy for the Cauchy in R.
To actually answer your question, assuming you have a good uniform RNG, and know how to generate exponential variates, I've attached the GSL C source for the Levy, which includes the Cauchy and Gaussian as special cases, and some extra comments in the code (although if speed is an issue, you can do better for the Cauchy and Gaussian.)  It's not 100% transparent, as it calls other GSL routines, but it should be obvious what's going on with those routines.
/* The stable Levy probability distributions have the form

   p(x) dx = (1/(2 pi)) \int dt exp(- it x - |c t|^alpha)

   with 0 < alpha <= 2.

   For alpha = 1, we get the Cauchy distribution
   For alpha = 2, we get the Gaussian distribution with sigma = sqrt(2) c.

   Fromn Chapter 5 of Bratley, Fox and Schrage "A Guide to
   Simulation". The original reference given there is,

   J.M. Chambers, C.L. Mallows and B. W. Stuck. "A method for
   simulating stable random variates". Journal of the American
   Statistical Association, JASA 71 340-344 (1976).

   */

double
gsl_ran_levy (const gsl_rng * r, const double c, const double alpha)
{
  double u, v, t, s;

/* gsl_rng_uniform_pos(r) returns a U(0,1) variate */

  u = M_PI * (gsl_rng_uniform_pos (r) - 0.5);

  if (alpha == 1)               /* cauchy case */
    {
      t = tan (u);
      return c * t;
    }

  do
    {
      v = gsl_ran_exponential (r, 1.0); /* Just use -log(u) where u~U(0,1) */
    }
  while (v == 0);

  if (alpha == 2)               /* gaussian case */
    {
      t = 2 * sin (u) * sqrt(v);
      return c * t;
    }

  /* general case */

  t = sin (alpha * u) / pow (cos (u), 1 / alpha);
  s = pow (cos ((1 - alpha) * u) / v, (1 - alpha) / alpha);

  return c * t * s;
}

Comment: Could you please post the pseudocode! GSL documentation is very difficult to understand
Comment: Here's the java version of my code http://pastebin.com/RcMhFsuZ. Please have a look. I would really appreciate it
Comment: @crucifiedsoul - your code looks fine to me.  Next time I'll give you Java code!
Comment: According to your code what will be the mean, standard deviation of Gaussian Distribution?
Comment: The mean will be zero, the standard deviation will be c*sqrt(2).


How to use API Documentation of dataset

Question: Some websites provide a link to a dataset (in Excel sheets format) which allows the dataset to be downloaded. But some others additionally provide API documentation, like this site. Can you please refer tutorials that explains about this concept, as well as how one may use it?
Answer: The API you've linked to is the HTTP API documentation, so you would need to able to perform HTTP requests to send get and post requests to the endpoint. Depending on your programming language of choice there are a ton of tutorials available, for example in python: https://www.datacamp.com/tutorial/making-http-requests-in-python
or https://www.geeksforgeeks.org/get-post-requests-using-python/
I don't know of tutorials for downloading from that specific provider, but the mechanics of http requests using the python requests library are roughly equivalent. For https://data.medicaid.gov/datasets, click on a specific dataset, then scroll to dataset API. From here you can get a single dataset, and if you click on the down arrow to the right of the text box you can try it out - button on the right. Then hit the Execute button and it will show you the curl commands and actually execute them as well as the request URL. So for example NADAC 2023, it will show https://data.medicaid.gov/api/1/metastore/schemas/dataset/items/4a00010a-132b-4e4d-a611-543c9521280f?show-reference-ids=false
This can be (roughly) translated into python using the requests library as
<code>response = requests.get('https://data.medicaid.gov/api/1/metastore/schemas/dataset/items/a217613c-12bc-5137-8b3a-ada0e4dad1ff/')
</code>
Of course, you then need to parse the response to find the actual location of the dataset ("downloadURL": "https://download.medicaid.gov/data/nadac-national-average-drug-acquisition-cost-09-06-2023.csv",) resend another request to download the actual data, and so on.
Comment: thanks for the answer, I have accepted your answer; but I noticed my question was not detailed enough. I am looking for tutorials that teach me how to download a dataset, for example by python code using the following information provided to download GET a Single dataset: /api/1/metastore/schemas/dataset/items/{identifier}

How to use API Documentation of dataset


Arp spoofing and ip detection

Question: I am testing two differents lan and I am tring to sniff traffic with Mitm attack using simple Linux shell command like arpspoof and whireshark to sniff the packets. In the first lan I can sniff without problem while in the second lan, using the same techniques, in whireshark I can see that is detected the use of the same ip for two differents MAC and I cannot see http protocol layer packets. Why in the first lan there are no duplicated ip? I thought maybe the switch arp table contains more than one entry with the same ip instead of containing only the modified row.
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
Answer: Switches don't have ARP tables, nor do they care about IP addresses. A switch will have a MAC address table that has a MAC address and the switch interface where the MAC address came in as the source MAC address.
The switch MAC address table contains a single entry for each MAC address. When you spoof a MAC address, it messes with the switch MAC address table, causing the interface for the MAC address entry in the table to keep changing.
MAC address spoofing is really about network disruption, rather than information theft. Multiple hosts claiming the same MAC address will cause the switch MAC address table to constantly change; some frames will go to one host, and some frames to another host.
When you use ARP spoofing, you are really spoofing the ARP cache in a host. The host with an incorrect MAC address for an IP address will send traffic for that IP address to that MAC address, and no other. This only works on a single LAN. If you are doing this across LANs, then you have a different problem: MAC addresses are only valid on the LAN where they exist, and any traffic destined for a different LAN gets sent to the MAC address of the host's configured gateway. You could spoof that, but then nothing from any host with the spoofed gateway MAC address will ever get off the LAN to another LAN.
Comment: Thanks. The two network I am working on are completely separated. It is just an example to say that arp spoofing one one works fine and there is no duplicated ip while in the other there is duplicated ip and I cannot sniff http layer. Maybe the problem is this duplicated ip. For example I have the gateway IP used by the real gateway MAC and the attacker MAC. Is it normal I think . . . ?

Arp spoofing and ip detection


Do I have to do ghusl if I only notice the stains but don't recall ejaculating?

Question: I noticed in my underwear that there was a stain from a white liquid that came out, but I didn't notice it at the time so will I have to to ghusl for this? The stain also didn't have a smell to it at all.
Answer: Yes absolutely and do not watch these types of videos because it is forbidden Allah ordered us to lower our gazes and you should stop this act and repent to Allah and see his forgiveness.


If $X \subset Y$ is a subspace and $W$ is arbitrary, then $\frac{Y \otimes W}{X \otimes W} \simeq \frac{Y}{X} \otimes W$

Question:
If $0 \rightarrow X \xrightarrow{i} Y \xrightarrow{\pi} Z \rightarrow 0$ is a short exact sequence and $W$ is a vector space, then the sequence
  $$0 \rightarrow X \otimes W \xrightarrow{i\otimes \text{id}_W}Y \otimes W\xrightarrow{\pi \otimes \text{id}_W}Z \otimes W \rightarrow 0 $$ is also exact. In particular,if $X \subset Y$ is a subspace and $W$ is arbitrary, then show that $$\frac{Y \otimes W}{X \otimes W} \simeq \frac{Y}{X} \otimes W$$

Before proving it, here is a small lemma that we shall need.

If $\phi:W \to Y$ and $\psi: X \to Z$ are injective linear maps, then $$\phi \otimes \psi: W \otimes X \to Y \otimes Z$$  is also injective.

Proof: Suppose that $\{w_i\}_{i \in I}$ is a basis for $W$. Let $v \in W \otimes X$. Then there exists a unique $\{x_i\}_{i \in I} \subset X$ such that $v =\sum_{i \in I}w_i \otimes x_i$. It is easy to see that $\{\phi(w_i)\}_{i \in I}$ (All but finitely many terms are non zero) is a linearly independent set in $Y$. If $\phi \otimes \psi(v)=0$, then we have $\sum_{i=1}^n \phi(w_i) \otimes \psi(x_i)=0$. Let $y_i^* \in Y^*$ be such that $y_i^*(\phi(w_j))=\delta_{ij}$ for each $i=1,2,\ldots,n$ and $j=1,2,\ldots,n$. Let $z^* \in Z^*$ be arbitrary. Then $$0=y_j^* \otimes z^*\left(\sum_{i=1}^n \phi(w_i) \otimes \psi(x_i)\right)=z^*(\psi(x_j))$$
Since this holds for all such $z^*$, we must $\psi(x_j)=0$ for each $j=1,2,\ldots,n$ which further implies that $x_j=0$ for each $j$, as $\psi$ is one to one. Thus, $v=0$.
From the above lemma, we see that $i \otimes \text{id}_W$ is one-to-one. Since $\pi$ is surjective, $\pi \otimes \text{id}_W$ is also surjective. Now we just need to show the exactness in the middle. Now suppose that $\{w_i\}_{i \in I}$ is a basis for $W$. Let $v \in \text{Image}(i \otimes \text{id}_W)$.Then there exists unique $\{y_i\}_{i \in I} \subset Y$ such that $v=\sum_{i \in I} y_i \otimes w_i$. Also there exists $u \in X \otimes W$ such that $v=i \otimes \text{id}_W (u)$. Moreover there exists unique $\{x_i\}_{i \in I}$ such that $u=\sum_{i \in I}x_i \otimes w_i$. Thus, we have $$\sum_{i \in I}y_i\otimes w_i=i \otimes \text{id}_W\left(\sum_{i \in I}x_i \otimes w_i \right)=\sum_{i \in I}i(x_i) \otimes w_i$$
which gives that $$\sum_{i \in I}\left(y_i-i(x_i)\right) \otimes w_i=0$$
By a similar argument as we did above, since $\{w_i\}_{i \in I}$ are linearly independent, we have that $i(x_i)=y_i$ for each $i \in I$. Since $\text{Image}(i)=\text{Kernel}(\pi)$, we have $\pi(y_i)=0$ for each $i \in I$. Thus, $\pi \otimes \text{id}_W(v)=0$.
For the other direction suppose that $v \in \text{Kernel}(\pi \otimes \text{id}_W)$. Then $v$ can be written as $\sum_{i \in I}y_i \otimes w_i$ for a unique $\{y_i\}_{i \in I} \subset Y$. Hence we have $\left( \pi \otimes \text{id}_W \right)(v)=\sum_{i \in I}\pi(y_i) \otimes w_i=0$. Again, since $\{w_i\}_{i \in I}$ are linearly independent, $\pi(y_i)=0$. So, $y _i \in \text{Kernel}(\pi)=\text{Image}(i)$ and hence can be written as $i(x_i)$ for some $x_i \in X$. Thus, $$v=\sum_{i \in I}i(x_i) \otimes w_i=i \otimes \text{id}_W \left(\sum_{i \in I}x_i \otimes w_i\right)$$
For the second part: We show the isomorphism between $\frac{Y \times W}{X \otimes W}$ and $Z \otimes W$ by exhibiting a right inverse from $\frac{Y \times W}{X \otimes W}$ to $\frac{Y}{X} \otimes W$ and left inverse from $Z \otimes W$ to $\frac{Y \otimes W}{X \otimes W}$.
How do I show this?
Thanks for the help!!
Answer: Because your tensor product is exact, all you have to do is take the short exact sequences
$$0 \to A\otimes X \to B\otimes X \to (A\otimes X)/(B\otimes X)\to 0$$
$$0 \to A \otimes X \to B \otimes X \to B/A \otimes X \to 0 $$
to conclude. The first is the canonical SES for a quotient, the other is the tensored SES of the SES for $A$ and $B$.
Comment: What about the way I am trying? How do I fix the issues that  have ?
Comment: You're having too much of an issue because you're looking at elements. Use universal properties. There is always a map from $(A\otimes X)/(B\otimes X)$ to $A/B\otimes X$ that completes the diagram of SES, and it is forcedfully an isomorphism in your casef.


What is the word that describes willingness of a human or even an animal to provide value to others in general?

Question: For example, willingness to provide for someone is generosity and willingness to protect someone is bravery, but if we wanted to put both of these (an possibly other values) under an umbrella term, what would that word be?
Comment: 'Willingness to protect someone'; is not the primary meaning of _bravery_.
Comment: You've given this the [single-word-requests] tag but do not appear to have followed [the guidelines for those questions](https://english.stackexchange.com/tags/single-word-requests/info). Please [edit] your question with the requested information as existing answers (including mine!) may not actually be what you need.
Answer: Altruism appears to fit:

uncountable noun
Altruism is unselfish concern for other people's happiness and welfare.
Synonyms: selflessness, charity, consideration, goodwill
— Collins

the principle or practice of unselfish concern for the welfare of others
the philosophical doctrine that right action is that which produces the greatest benefit to others

— ibid.
Answer: If you provide for someone, then you are kind to them; similarly, if you protect them, it is often out of kindness, or that's what it amounts to anyway, kindness. As well, if you favour people with special advantages, which means that you make available to them certain opportunities of value, or, in the words of the OP, if you "provide value" to them, then, again, this is done out of kindness. So it seems to me that "kindness" is an umbrella term, at least a basic one.

(OALD)
kind adjective
(comparative kinder, superlative kindest)
caring about others; gentle, friendly and generous
• a very kind and helpful person

(OALD)
kindness noun  [uncountable]
the quality of being kind
• to treat somebody with kindness and consideration


Should a playlist be deleted after deleting it's videos?

Question: User can upload videos and create playlists with that videos. What would happen if the user deleted videos used in a playlist? Should a playlist be also deleted?
Answer: Should the system delete an empty playlist?
No. Because I've just removed the content (songs, videos, photos etc.) from that playlist or folder. I might want to add new videos to the same playlist later in future. But, a system should give an option to delete the playlist if user wants to.
Answer: Additionally to @Dipak's answer.
Lets say a user has a playlist with 3 elements. The user deletes element 1. After he deletes element 2. When he deletes element 3, he might not realize the playlist will end up "empty". So when the user deletes the last element you could:

inform him that the list will be empty
ask if he also wants to delete the list

Otherwise the user will wonder why the list isn't showing where it should.
An empty list might need to have a different display than a filled one.
Answer: I also believe that it shouldn't delete the playlist.
Making the analogy of a playlist as a "folder": the same situation if you create a folder on Gmail and it doesn't have any email inside; the folder continues to exist. The same if you have a folder on your OS and took all the files from it. The folder is still there.


Interface Contract, Class Object?

Question: Is contract to interface as object is to class?
What is the need to differentiate identical things like this, from the code to the executing code?  I sort of get the idea behind naming a class a class and the instantiated executing class an object, but overall, is that the only reason for these semi-redundant terms?
Comment: I see the difference now, thx for the answers.  I've used them for years, albeit well and accurately from what I've seen, but I never really stopped to actually think the definitions through.
Answer: Not really. There are four terms here, so I'll go over each of them:
Interface
An interface is an abstract class (in languages like Java where there is no multiple inheritance, sometimes there are other restrictions, such as a separate data type) that is intended to be used as a common base to access a number of similarly-behaving objects. Conceptually, there is no requirement for abstractness, but usually, an interface will have at least one abstract method. An interface is a method for your program to communicate with a number of similar classes, each with different semantics but the same general purpose.
Contract
A contract is the implicit agreement you make between users and implementers of a class or interface. For instance, preconditions and postconditions (invariants are usually a contract within the class' implementation - generally, things like the relation between internal members don't need to be exposed). The specification for a return value or an argument can also be part of the contract. It basically represents how to use the function/class/interface, and isn't generally fully representable in any language (some languages, like Eiffel, allow you to put explicit contracts in, but even these can't always fully flesh out the requirements). When you implement an interface or derive from a class, you are always having to meet the interface requirements, or, when overriding a non-abstract class, to behave similar enough that an external viewer doesn't notice the difference (this is the Liskov Substitution Principle; a derived object should be capable of replacing the base with no difference in behavior from the outside perspective).
Class
A class doesn't need a lot of going over, since you clearly have used them before. A class is the data type, and in some languages is a superset of interfaces (which have no formal definition, as in C++), and in others is independent (such as in Java).
Object
An object is an instance of a class type (or of any non-class type, usually). The exact definition of an object is very specific to a language, but the general definition is the actual thing referred to by multiple references/pointers to the same thing - for instance, in some languages like Java, == compares whether two variables are the same object, not necessarily whether they are semantically the same. Objects are independent from classes or interfaces - they represent a single instance. Another way of thinking of it is that class or interface is the mold, and the object is the physical object that comes out of the mold (a rather bad analogy, but it's the best I can come up with right now).
Comment: Not sure about other languages, but in C# `interface` and `abstract class` are similar, however are different concepts; they are not the same and cannot always be used interchangeably.
Comment: I would not still omit the "implicit" - that doesn't necessarily describe the nature of what I understand as contract.
Generally a type system allows the programmer to express constraints on implementations. As such, a type definition - such as an interface in Java - can very well be viewed an explicit contract which is fulfilled by a type implementing it.
Comment: See for example this cseducators post:
https://cseducators.stackexchange.com/questions/544/explaining-how-an-interface-is-a-contract
Answer: No, not really.  A class is a template that you define.  Each object that instantiates that class follows the template.  They're not really redundant terms, because the two things are not identical.  You can think of a class as a user-defined data type.  Classes and objects are different from each other in the exact same way that the primitive data type int is different from the literal value 3.
An interface defines a set of methods that all implementing classes must support.  The interface itself is the contract that you define for the implementing classes.  It just says that any class that implements the interface, must have that interface's set of public methods.
Answer: Well I guess... if an interface specifies a contract than a class specifies an (or multiple) instance(s) of a particular object.
Terminology is less important than application though.
Answer: Actually, an interface is a contract, when an object is an instance of a class - they are different things that don't have too much in common.
The interface just provides a facade for objects, or a warranty for the caller that the object can do some operation, even without knowing it's implementation.
For example, you can have two classes implementing the same interface/contract, but do totaly different things (even though the meaning of doing them may be the same).
Take the IDisposable interface for example: Each object can release the resources that it uses, but it can do it in many different ways, it can choose not to release anything. It's the object's choice.
At least this would be the POV in .NET
Answer: To complete the previous answers, a word about interfaces:
If the class is more than a template for an object (because of its global characteristics independent of any instances), the interface can be also be described  as a point of view
A class implementing several interface:

complete the contract it needs to respect
allow the user to see any instances of that class from the point of view of the one represented by the implemented interface.

"Point of view" means you can using an object by focusing solely on the contract define by that interface.
It is in that aspect an interface is an "abstract class", as in an "abstraction" (something which takes after some of the characteristics of a class, but leave some others out). In java world, an interface leaves actually a lot out, since it can only be applied to define contract for instance, not for static methods or functions.
Answer: "Class" and "Object" represent two different things; they are related, but what they represent IS different, quite strongly.
The best way to describe this is to look at Static.  A class can have static members, which are completely separate from any INSTANCE of that class.  Objects of that class may or may not use those static members; but the instance of the object of that class is completely separate from any static uses of that class (or should be, at the very least).
Or think of the singleton pattern.  Storing an instance of the class object in a static class accessor is a common practice, and shows the difference.  You refer to the class static accessor to get the object instance of a singleton class; if the class static member does not have an object instance to refer to, the class creates the instance of the object.
Put another way; an object is an instance of a class; but a class can be more than just a template from which objects are instantiated.  Static members of classes have a representation in memory that is completely independent of object instances of those classes.

Interface Contract, Class Object?


How can I prove complex limits using epsilon delta definition?

Question: How can I prove that $$\lim _{z \to i} \frac {iz^3-1}{z+i} =0$$
Using the epsilon-delta definition I get stuck after factorizing $iz^3-1$ to get $$\left|\frac {(1+iz)(z^2+iz-1)}{z+i}\right| < \epsilon $$
Usually what I would do is get a $|z-i|$ term somewhere and then try to bound the other terms (at least that is what I did with real limits) how can I go around this problem? What am I doing wrong?
Comment: A general method one can use (for this problem there is simpler ways): The numerator (which is a qubic polynomial) vanish for $z=i$ so we can write it on the form $iz^3 - 1 = a(z - i)^3 + b(z-i)^2 + c(z-i)$ for some constant $a,b,c$. Since the leading term is $iz^3$ we must have $a=i$. The rest of the constants can be figured out by expanding and comparing to the left hand side (or using calculus; comparing derivatives of the two sides at $z=i$).
Answer: Factoring $i$ out of $1+zi$ gives $i(z+\dfrac{1}{i})=i(z-i)$.
Answer: From @user247327's hint, which is to factor the term $i$ out of $1+zi$, results in $$\left|1+iz\right| = \left|i(z+\dfrac{1}{i})\right| = \left|i\right|\left|z-i\right| = \left|z-i\right|.$$
Therefore,
$$
  \left|\frac {(1+iz)(z^2+iz-1)}{z+i}\right| =
  \left|z-i\right|\left|\dfrac{z^2+iz-1}{z+i}\right|.
$$
From this, try to bound the numerator and denominator of $\left|\dfrac{z^2+iz-1}{z+i}\right|$ by finding an appropriate disc of radius $\delta$, i.e. determine $\delta>0$ such that
$$
  0<\left|z-i\right|<\delta={}\operatorname{min}\left\{1,\text{some expression of }\epsilon\right\}
$$
and $\left|\dfrac{(1+iz)(z^2+iz-1)}{z+i}\right| < \epsilon$.


C.elegans and antioxidants

Question: How would you test the effect of antioxidants on C.elegans lifespan?
Is this done through feeding E.coli with antioxidants and then C.elegans with E.coli, or is there another method?
Answer: base on a article they do the test of nano-Pt, kind of SOD, and they do the experiment in several steps, first choose C. elegans strains and growth conditions, meanwhile prepare the nano-pt. then, do the lifespan assay. thired is Oxidative stress resistance. the last step is Fluorescence microscopy. in the mictoscopy they do several steps, include Measurement of lipofuscin accumulation, Detection of ROS, Measurement of SOD/catalase activit, Thermotolerance and Effects of dietary restriction
Answer: You can simply add the molecule of interest in the NGM or Liquid medium.
From this paper.

The worms were bleach-synchronized as follows: 2 mL of 6% NaOCl were
  mixed with 1 mL of 5 M NaOH per 7.5 mL of concentrated worm
  suspension, and shaken for 4–7 minutes until the carcasses dissolved
  as monitored by direct observation. The remaining eggs were then
  washed 3 times by pelleting at ~1150 g for 2 minutes at room
  temperature, followed by aspiration of the supernatant and
  resuspension in 50 mL of 0.1 M NaCl. A final pellet of eggs was
  obtained by centrifugation at ~1150 g for 2 minutes at room
  temperature, followed by aspiration of the supernatant. Eggs were then
  added to a 250 mL liquid culture, as described above. For experiments
  without RNAi treatment, bacteria were heat killed at 80°C for 60
  minutes. The worms were cultured at 20°C and monitored until they
  reached adulthood (~72 h), at which time FUdR was added to a final
  concentration of 400 µM. Worm viability was scored every two days by
  taking ten 10 µL drops (initially ~20 worms per drop) of the culture
  and counting the living worms under a microscope. The average number
  of living worms was then calculated. S medium or deionized water
containing 10 mM malate, succinate, or fumarate was added back every
  three days to compensate for metabolism of the compounds and
  evaporation, and S medium containing FUdR and bacteria was replaced
  every 6 days. At least two replicates of each experiment were
  performed.

C.elegans and antioxidants


If a creature is hiding within a pile of something can it take 10 on its hide check?

Question: Here is my scenario. The PC's are adventuring through a town filled with piles of dead fish. Within some of these piles are medium sized crabs which will ambush the PC's if they come close to their pile of yummy fishes. The question is when the PC's walk past the pile I assume they would make a spot check against the crabs hide check. But as the crab is hidden and technically not currently threatened could it take 10? Or does it have concealment? Or just a circumstantial bonus to hide? I am confusing myself here...
Comment: [Related.](https://rpg.stackexchange.com/q/35977/8610)
Answer: Hide checks typically aren't made until observation's possible
A creature (like a Medium monstrous crab) with concealment or cover (like beneath a Large pile of dead fish) makes its Hide skill check when potential observers have line of sight of to the place where the creature's hidden. Prior to the presence of any potential observers, it doesn't matter whether the creature's hidden or not (since no one's around to observe), so the game doesn't care, either. For this reason, taking 10 (and, similarly, taking 20) on Hide skill checks is normally impossible: a creature's Hide skill check is opposed by potential observers' Spot skill checks, and a creature trying to hide is usually "threatened or distracted" by the presence of potential observers.
However, taking 10 on Hide skill checks when time allows is a reasonable house rule—and one that this DM uses on occasion—as it gives some advantage to setting up ambushes. For example, a poor roll by one goblin raider no longer betrays the goblin raiders' presence, and lucky rolls by all the goblin raiders won't leave the PCs at a tactical disadvantage despite some PCs having invested heavily in the Spot skill. Note that this DM does not have a house rule that allows taking 20 on Hide skill checks—taking 20 typically involves multiple attempts to use a skill until getting it right, and allowing a creature to determine exactly the point at which it is perfectly concealed to the best of its ability is just too much for this DM. Nonetheless, a this player wouldn't reject out of hand another DM making a house rule saying differently, especially were observers present to provide feedback on the hiding creature's performance.
Comment: There are situations wherein taking 20 is reasonable, for example if your goal is to hide past 10 o clock in a city with a 10 o clock curfew but you can just poof away with no ill effects each time you fail, it makes sense to just skip time till the time you do the best you could, if there's no pressure.  Such situations are just exceedingly rare.
Comment: @thedarkwanderer Absent an onlooker to judge, I just don't know how the creature trying to take 20 on its Hide skill check *knows* it's finally hidden as best it can. I mean, you can reality check this if you want. Go hide somewhere. Now, without outside input, *how well* are you hidden? And, more importantly, *How do* you *know how well you're hidden?*


Is it possible for someone with juvenile felony charge (not conviction) to join the military?

Question: If someone were charged with a felony in the US (e.g. sexual assault, harassment, or murder) as a juvenile, but they're not convicted (their case or the charges were dropped), can they join the military after they turn 18? If not, then why?
Answer: According to the US Army's web site, which gives an overview of the entry requirements, the minimum age is 17 and it seems that only felony convictions and juvenile offences are a bar to recruitment - however the Army Recruiter should be able to confirm whether or not dropped charges fall in to these categories or exclude a candidate for any other reason.
Section 1 "meeting with a recruiter" section includes this:

Your local recruiter will conduct a prescreening to see if you qualify for enlistment. At the recruiting station, he or she will ask you about your:

Education level

Criminal history

Age

Marital/dependency status

Physical condition

And one of the "see if you pre-qualify" quick-quiz questions asks if one's age is between 17 and 34
Section 2, "required documents", includes this:

The U.S. Army makes every attempt to assess the moral quality of potential recruits. To this end, a thorough background check is done on all prospects.

It is imperative that you disclose all legal offenses

Felony convictions will result in candidates being exclude

Drug and domestic violence charges will exclude candidates (Some minor drug offenses may be waived on a case-by-case basis)

Juvenile offenses will also exclude you

Certain Army jobs requiring higher security clearance may necessitate more thorough investigations
Comment: Shorter: A non-conviction does not categorically disqualify you. A "juvenile offense" is a form of conviction. It probably requires explanation, however, and might conceivably limit your access to high security clearance jobs if the folks evaluating the background check for a security clearance think that the circumstances of the non-conviction crime cast enough doubt (even though not beyond a reasonable doubt of conviction) on your trustworthiness.


How close can villagers move to your house?

Question: My house sits 5 spaces away from a cliff (meaning I could make a horizontal line of 5 flowers between my house and the cliff, for example). Knowing that a villager's house has a width of 3 (size is 3x3), can a villager move in between my house and the cliff?
Answer: After a bit of digging I found that... YOU will always maintain the shape of your house, no matter how much you upgrade it.  You also have the protection of a 1x1 "No Build" zone around your house.  Essentially it just means you need to be able to move freely in this area.  VILLAGERS also need to follow these standards.  They need a 3x3 plot PLUS the 1x1 free space around their home.  So!
They would not be able to squeeze their house between you and the cliff because they do not have enough room due to not having the 1x1 "Walking Path" around their plot.  I hope this helps!
Thanks to GameFAQs for the Info! (Two Links there)
Answer: When I built my house it was in the middle of trees. Now there is a villager's house four spaces away from me and another three spaces away and another six spaces away.
Comment: Can you elaborate on this at all? Perhaps provide a picture explaining just how far away things are.


Japanese Acer tree, roots have grown through bottom of pot

Question: I have a Japanese Acer tree in a pot. The roots have grown through the bottom of the pot and into the ground. I don't think they can have gone deep as under the pot is gravel and then weed control fabric  I think I need to repot the tree but don't want to risk  killing it as I really like it.
Can you tell me the best way to go about separating it from the ground and then reporting it?  If I have to break the pot it's not a problem. Thank you.
Answer: This often happens with potted plants stood on anything other than a hard surface such as paving, I'm afraid. It's hard to estimate how far down the roots may have penetrated the ground beneath, though the size of the plant in comparison to its pot can be a useful guide.
There is, though, no choice but to remove or break the roots which have gone out of the pot - you can try digging around to see if you can loosen and extract as much root material as possible, but usually, its not possible to get it all because its difficult to move the pot out of the way to gain proper access, and they will have to be cut off.
If the root coming out of the pot is thick, then you may need to break the pot, but if they're just fibrous, it might be possible to extract the plant, leaving the pot intact, otherwise, cut it off. Have ready a larger pot with drainage holes and some fresh potting soil - if the rootball of the Acer, once unpotted, is very dry, soak it in a bucket of water for an hour or so, then transfer to the new pot, packing in new potting soil beneath and around it. Water in well, allowing excess to drain away freely from the bottom of the pot. And this time, stand the pot on something to keep it off the surface below (pot feet or bits of broken tile, whatever); this will prevent the same thing happening again.
Keep well watered - if the top starts to die back because of the loss of root material, you may need to cut down the Acer by up to a third to reduce the strain on it of trying to keep its leaves alive. Alternatively, wait until Fall and do it then, when the plant is no longer supporting foliage and growth in the upper parts.
Comment: Thank you so much for taking the time to give me such an in depth answer. If there's less risk to the tree, I'll wait until Autumn as I don't want to damage it.
Comment: Ah, autumn you say - does that mean you're in the UK? If so, do it late September if you're in the north, October in the south and west...
Comment: Yes I'm in the UK, North West. I will set a reminder on my calender for early September to get everything ready. I don't know how to put a photo on here or I would put a photo of the tree on for you to see it. Thanks again


What's a good way to encapsulate data access with PHP/MySQL?

Question: Most of my experience is on the MSFT stack, but I am now working on a side project, helping someone with a personal site with cheap hosting that is built on the LAMP stack.  My options for installing extras are limited, so I'm wondering about how to write my data access code without embedding raw queries in the .php files.
I like to keep things simple, even with .NET.  I generally write stored procedures for everything, and I have a helper class that wraps all calls to execute procedures and return data sets.  I'm not looking for a full-blown ORM, but it might be the way to go and others who view this question might be looking for that.
Remember that I'm on a $7/month GoDaddy account, so I'm limited to what's already installed in their basic package.
Edit: Thanks rix0rr, Alan, Anders, dragon, I will check all of those out. I edited the question to be more open to ORM solutions, since they are so popular.
Answer: ActiveRecord seems to be the state of the art at the moment. I can't recommend any good PHP frameworks for that though. I tried Propel which, while nice, is not easy to set up (especially on a host that you can't install anything on).
Ultimately, I rolled my own ORM/ActiveRecord framework, which is not too much work and very instructive. I'm sure other people can recommend good PHP frameworks.
Answer: Take a look at the Zend Framework, specifically Zend_Db. It has a Database Abstraction layer that doesn't require anything other than the MySQLi extension to be installed and isn't a full-blown ORM model.
Answer: Maybe Doctrine would do the job? It seems to be inspired by Hibernate.
Answer: rix0rrr hit on it a bit, in that many tools are a pain to set up. Of course, I have my own solution to this problem that has been working quite well for the past few years. It's a project called dbFacile
I also wrote a bit of a usage comparison of the tools I found a few years ago. It's incomplete, but might give you a good starting point.
You mentioned that you don't want to embed raw queries but you don't want ORM, so I'm a bit confused about the middle ground you're hoping to find. I also have an ORM project that aims to require minimal setup and great ease of use.
The only requirement for my projects is PHP5.
Answer: I would try a framework. Zend Framework has been cited. Symfony seems interesting. It's based on ideas from Ruby on Rails.
Answer: You could also take a look at Prado.  http://www.pradosoft.com/  It uses Active Record and DAO.  Also if you use .Net then some of the formatting and conventions are similar.


Is it true that any current smartphone is broadcasting audio and position of its owner even if switched off and not given permission by the owner?

Question: Is it true that any current smartphone is broadcasting audio and position of its owner by design even if switched off and not given permission by the owner to broadcast?
Comment: Where did you hear that?
Comment: So, you were told verbally? I'm afraid it is up to you and the person who told you to back up these claims. We cannot defend every random things people say to each other.
Comment: I think you are going to have to cite where you heard this. It is so sweeping of a statement that I think you might have lost some context.
Comment: All phones everywhere regardless of maker?
Comment: @schroeder I can tell you who told me if you tell me the benefit of knowing who said it.
Comment: Are you thinking of e911 perhaps?
Answer: This statement is not completely accurate.
The second part, "...and position of its owner...", requires the smart-phone to have a particular type of a gps tracking chip in it. This, I believe, is different than the usual "Turn on GPS so I can find my phone if I lose it" feature.
About the first part, "...broadcasting audio ... even if switched off ..."
This is possible under certain conditions. Short answer -- this does NOT happen.
What you are referring to is, basically, malware. In order for this malware to be installed on your phone, the following things need to happen:
1. The attacker needs a reason/motive to install it.
2. The attacker has to know the OS of your phone & have the appropriate software for that OS.
3. The attacker must have PHYSICAL ACCESS to your phone. (i.e. physically have it in his/her hand)
4. The attacker needs to have it unlocked & have a Cell-phone hub, capable of talking to your phone, available when it is physically available.
So, have you made anyone angry lately? Do you have any information that some-one else may want? Have you lent your phone to someone who has the equipment to do such a thing lately?
So, basically, you don't need to worry about it.
Note: Yes, I do know the source of this information. No, I cannot say.
Answer: The answer that can be relied on pretty much 99.9% of the time is 'no'.
For the audio part of your question: Probably some phones, somewhere, might do this if they are located in an area with an extremely nosy government. There is something they inadvertently agreed to that allowed their phone company to mine their data, or a government agency needs to spy on your phone for National Security. Also, your phone could be hacked. But no, about 99.9% of phones do not record your audio. It is an incredibly rare occurrence that they do.
For the location part: This is partly correct. While your ISP can track you as long as there are at least three strong signal towers that are capable of pinging your phone in the area, they do not track you unless a similar scenario to the ones mentioned above happens.
If you are truly so paranoid that all phones are out to get you, I have two possible solutions for you.
Solution one: disconnect from cellular data at all times, run a trusted AV at least twice a day( please do your research before downloading a random one off the internet), and when you use wifi, only use trusted networks and configure your phone to route all your traffic through Tor.
Solution two: Destroy your phone with a hammer (please don't)
When your phone is off, the same answer applies. People can still track you and record your audio, but it is EXTREMELY unlikely and quite difficult.
Assuming your phone is off: For most phones, some core functions will continue until the phone is powered off. If the hacker's attack is sophisticated enough, they will be able to exploit said features into gaining privileges to use the microphone, thus recording audio. However, as long as you are disconnected from wifi and cellular, the attacker will not be able to use any information they have exfiltrated until you regain some sort of internet connectivity.
Comment: This does not answer the case in the question *for when the phone is off*. All your scenarios are for when it is on.
Comment: I actually did solution two a couple of years back. Don't do it. The destroyed phone got extremely hot, I threw it in the garden and it set fire and exploded.
Comment: You are going to have to explain how it is possible to record audio when the device is off.


How to remove splash screen from my acer aspire laptop running ubuntu 16.10

Question: I have a Acer laptop running ubuntu 16.10 . I got this laptop from government for my good marks but every time I boot my laptop I have to see a creepy image of our chief minister after this image ubuntu logo appears. I want to remove this chief minister"s photo (splash screen). When I got this laptop it was running win 10 with same boot picture. Later I moved to ubuntu but the boot image is still there.
Answer: Press F2 when you see the chief minister's face, you should be taken to a screen labelled "Setup utility" or similar, there should be a boot tab, under the boot tab there should be an option labelled "show boot logo" or similar
press enter and highlight disabled and your problem should be fixed. The boot logo option may not be under the boot tab. In that case you will need to look in all the tabs for such and option.
Comment: Thanks for the answer . But there is no option in bios (boot).
Comment: @GauravThakur If so I'm afraid you'll ave to get used to your chief minister's face, or obtain a new computer. FYI, this has nothingto do with Ubuntu.


Difference between getAttribute() and getParameter()

Question: What are the differences between the getAttribute() and the getParameter() methods in HttpServletRequest?
Comment: Related: [How to servlets work? Application/Session/Request scopes?](http://stackoverflow.com/questions/3106452/how-do-servlets-work-instantiation-session-variables-and-multithreading)
Comment: In what class/package/API?  Did you try reading the JavaDocs for the relevant methods?
Comment: attribute is only for http request  that helps servlets work together
Answer:
getParameter() returns http request parameters. These are passed from the client to the server. For example http://example.com/servlet?parameter=1. They can only return String.

getAttribute() is for server-side usage only - you fill the request with attributes that you can use within the same request. For example - you set an attribute in a Servlet and read it from a JSP. These can be used for any object, not just string.
Comment: I suppose when you use something like `${attrName}` in a jsp page, those are the attributes you set using `request.getSession().setAttribute()`?
Comment: Since request attribute are stored on server side, can I set request attribute for a inter-server post-redirect-get request? I want to send information from one server to another server in JSF through an attribute in redirect request. I am able to send via a POST request as of now.
Comment: In this case, "Parameter" seems to be synonymous with "query string"
Answer: Generally, a parameter is a string value that is most commonly known for being sent from the client to the server (e.g. a form post) and retrieved from the servlet request.  The frustrating exception to this is ServletContext initial parameters which are string parameters that are configured in web.xml and exist on the server.
An attribute is a server variable that exists within a specified scope i.e.:

application, available for the life of the entire application
session, available for the life of the session
request, only available for the life of the request
page (JSP only), available for the current JSP page only
Comment: "Generally, a parameter is a string value" Other than *strings* what could we be sending?
Comment: ^Objects as in the case of request.setAttribute
Answer: request.getParameter()
We use request.getParameter() to extract request parameters (i.e. data sent by posting a html form ). The request.getParameter() always returns String value and the data come from client.
request.getAttribute()
We use request.getAttribute() to get an object added to the request scope on the server side i.e. using request.setAttribute(). You can add any type of object you like here, Strings, Custom objects, in fact any object. You add the attribute to the request and forward the request to another resource, the client does not know about this. So all the code handling this would typically be in JSP/servlets. You can use request.setAttribute() to add extra-information and forward/redirect the current request to another resource.
For example,consider about first.jsp,
//First Page : first.jsp
<%@ page import="java.util.*" import="java.io.*"%>
<% request.setAttribute("PAGE", "first.jsp");%>
<jsp:forward page="/second.jsp"/>

and second.jsp:
<%@ page import="java.util.*" import="java.io.*"%>
From Which Page : <%=request.getAttribute("PAGE")%>

Data From Client : <%=request.getParameter("CLIENT")%>

From your browser, run first.jsp?CLIENT=you and the output on your browser is
From Which Page : *first.jsp*
Data From Client : you

The basic difference between getAttribute() and getParameter() is that the first method extracts a (serialized) Java object and the other provides a String value. For both cases a name is given so that its value (be it string or a java bean) can be looked up and extracted.
Comment: This was a great example. This should be the accepted answer. The accepted answer is correct but for new comers an example clarified everything. Thank you.
Comment: Great answer. Maybe worth adding that scope of attributes come into play when you intercept a client's request server side and append some additional information to the request.
Answer: It is crucial to know that attributes are not parameters.
The return type for attributes is an Object, whereas the return type for a parameter is a String. When calling the getAttribute(String name) method, bear in mind that the attributes must be cast.
Additionally, there is no servlet specific attributes, and there are no session parameters.
This post is written with the purpose to connect on @Bozho's response, as additional information that can be useful for other people.
Answer: The difference between getAttribute and getParameter is that getParameter will return the value of a parameter that was submitted by an HTML form or that was included in a query string. getAttribute returns an object that you have set in the request, the only way you can use this is in conjunction with a RequestDispatcher. You use a RequestDispatcher to forward a request to another resource (JSP / Servlet). So before you forward the request you can set an attribute which will be available to the next resource.
Answer: -getParameter() :

        <form name="testForm" method="post" action="testJSP.jsp">
            <input type="text" name="testParam" value="ClientParam">
            <input type="submit">
        </form>

    <%
    String sValue = request.getParameter("testParam");
    %>
    <%= sValue %>

request.getParameter("testParam") will get the value from the posted form of the input box named "testParam" which is "Client param". It will then print it out, so you should see "Client Param" on the screen. So request.getParameter() will retrieve a value that the client has submitted. You will get the value on the server side.
-getAttribute() :
request.getAttribute(), this is all done server side. YOU add the attribute to the request and YOU submit the request to another resource, the client does not know about this. So all the code handling this would typically be in servlets.getAttribute always return object.
Answer: getParameter - Is used for getting the information you need from the Client's HTML page
getAttribute - This is used for getting the parameters set previously in another or the same JSP or Servlet page.
Basically, if you are forwarding or just going from one jsp/servlet to another one, there is no way to have the information you want unless you choose to put them in an Object and use the set-attribute to store in a Session variable.
Using getAttribute, you can retrieve the Session variable.
Answer: from http://www.coderanch.com/t/361868/Servlets/java/request-getParameter-request-getAttribute

A "parameter" is a name/value pair sent from the client to the server
  - typically, from an HTML form. Parameters can only have String values. Sometimes (e.g. using a GET request) you will see these
  encoded directly into the URL (after the ?, each in the form
  name=value, and each pair separated by an &). Other times, they are
  included in the body of the request, when using methods such as POST.
An "attribute" is a server-local storage mechanism - nothing stored in
  scoped attribues is ever transmitted outside the server unless you
  explicitly make that happen. Attributes have String names, but store
  Object values. Note that attributes are specific to Java (they store
  Java Objects), while parameters are platform-independent (they are
  only formatted strings composed of generic bytes).
There are four scopes of attributes in total: "page" (for JSPs and tag
  files only), "request" (limited to the current client's request,
  destroyed after request is completed), "session" (stored in the
  client's session, invalidated after the session is terminated),
  "application" (exist for all components to access during the entire
  deployed lifetime of your application).
The bottom line is: use parameters when obtaining data from the
  client, use scoped attributes when storing objects on the server for
  use internally by your application only.
Answer: Another case when you should use .getParameter() is when forwarding with parameters in jsp:
<jsp:forward page="destination.jsp">
    <jsp:param name="userName" value="hamid"/>
</jsp:forward>

In destination.jsp, you can access userName like this:
request.getParameter("userName")

Answer: Basic difference between getAttribute() and getParameter() is the return type.
java.lang.Object getAttribute(java.lang.String name)
java.lang.String getParameter(java.lang.String name)

Comment: you are not rigt about this.


How to do inter process communication using single bidirectional pipe in linux?

Question: How do 2 processes communicate by using single bidirectional pipe, such that both the ends of the pipe could read and write.
Comment: Yet another valid question being closed for the wrong reason?  This question doesn't ask for learning material at all.  It simply asks for help!
Answer: You don't. Pipes are unidirectional: you write at the write end, and read from the read end.
If you want bidirectional communication, use a socket, or two pipes.
You can use a pipe for bidirectional communication if both processes keep both ends of the pipe open. You need to define a protocol for whose turn it is to talk. This is highly impractical.


Can one person value two other persons equally?

Question: If one thinks deeply enough about the subjective value they place on their connection to other individuals, would they discover clearly distinct rankings of value?
Comment: In some cases, multidimensional metrics can be reduced to a single dimension. But not always. It's legitimately possible to have two separate metrics that can not be combined into a single metric.
Comment: This assumes valuation is one-dimensional. It's possible to value X greater than Y under one measure, but Y greater than X under another measure.
Comment: The combination of many 1 dimensional metrics can net together into a multidimensional metric. It could be that you prefer one person for x reason more often across time than you prefer another person for y reason. This maybe why people are valued similarly to begin with. It might be too much effort for too little gain when it comes to searching for how much one values another.
Answer: (This is an extended comment, not a properly sourced answer)
I have a feeling that you are looking for an explanation where it is shown that loving/treating two or more people equally results in some sort of contradiction or fallacy. That is not the case. Based on logic alone, there's no apriori reason that an agent can't assign the exact same value/ranking to two distinct entities (or more).
There might be empirical evidence suggesting that it is impossible to value two other people equally, but that would be a question for psychologists, not philosophers.
There is a case to be made that "loving" or "valuing" a person looses its meaning if it is applied to too broad a category. I was part of a large social circle that included over a 100 people, and another member of the group told us once that she loved each and every one us and that we were all her special friends. I remember thinking to myself that her statement doesn't really make sense: By definition, a friend is someone you single out for special treatment compared to other people. if everyone in the group was her special friend, then there was nothing special about the friendship. Another way of looking at it is: If everyone is a VIP (Very Important Person), then no one is a VIP - VIP by definition should apply to a small number of people compared to the overall group.
So although there is no contradiction in valuing more than one person, there is some sort limit on how many people you can value, before the term looses it's meaning.
In the case of your earlier post about polyamory - which this seems to be a follow up on - there is no inherent contradiction in the idea of polyamory itself. It is possible to say however, that beyond a certain number of partners, the person is no longer polyamorous, they are simply promiscuous.
Comment: I think the polyamory one is more complicated. There may be legitimate questions in the domain of biology, neuroscience, or elsewhere about having multiple sexual lovers and all that works, but I strongly agree that there's no automatic fallacy in loving two people to the same extent.
Answer: I think one thing that would help your line of questioning a bit is that you can restrict your question to this: can you love two people maximally and equally.
It seems obvious and intuitive that I can love/value people equally. For instance, there's a category of people who I do not know. For such people, I value them as human beings and from this ascribe to them moral value. As far as I can tell all such people are people I value equally.
There's also a lot of open questions as demonstrated by the comments whether valuing/loving people can be reduced to a single composite value (or perhaps whether even if there are numeric (or more generally ordinal) values for valuing people).
For instance, I may have friends that I love playing board games with, and other friends that I like to talk about heavy matters with, but I might "love them equally" under some valuation.
It seems the area where this might pose an issue is something like this:

Can I have two number ones in my life?

Here, I think there's more of an open question than "can 2000 people be tied for #1000" in terms of my valuing people. The less high up on the hierarchy there more obvious it is that there can / could be ties.
But then it's hard to think of what specific philosophical resources one can use to look at this question.
Here's some suggestions for possibly sympathetic views:

Aristotle's Nicomachean Ethics BK I -- on the good we pursue in life, the concept of eudaimonia and BK VIII - on friendship and its different forms. (See for instance his critique of Plato's Republic and the idea of common children and his ideas about the nature of family).
Kierkegaard's Works of Love. A helpful secondary source is M. Jamie Ferreira who works through different sections. I don't know what would be the best section for help with your question (or line of questions).
Kierkegaard's Fear and Trembling. On it simplest level, it asks does loving God mean hating Isaac? For the contra, Levinas' Totality and Infinity. And all of the secondary literature on this are basically about the question of whether and how having different loves relates.
The Confucian Analects -- though you would definitely need a guide to interpret it. And Mencius.
Interestingly, Hegel, especially in the Philosophy of Right.

For literature that would tend to disagree with you:

I feel like Sartre and de Beauvoir both wrote things about love that would strongly disagree with what you're suggesting.
Michel Foucault, History of Sexuality
Many contemporary interpreters of Kant somehow get a polyamory or something like that out of him (even though his own views are greatly opposed to it).
Answer: The 'two causes' (or the persons) of one's birth are equally important. So people give equal importance to their parents.
In the case of identical twins also most of us value them equally until we  know closely.
Good mothers value their children equally.
Sanyasins, when they are in a higher level, value everybody equally.
Comment: This is an interesting point, although by the time a child matures enough to start having subjective values they will have found one parent to be a better caretaker, or more agreeable.
Comment: That is right. But I didn't mean all people. I meant about normal case.
Answer: Certainly, but the logic would likely be fuzzy (T/F for any given aspect of affinity can be a value between 0 and 1). Certainly relationships can have a utility function.
In terms of valuing two other people equally, there is no mathematical or philosophical reason one cannot, unless the sorting algorithm requires a clear hierarchy with no ties...
Answer: Your question has a common language issue: what is "value two other persons equally"? So, the answer is yes and no.
Yes, because all our interactions end up in one final and binary outcome: attraction or rejection. So, if you feel attracted to your father and mother, you value two other persons equally.
No, because for the outcome above, we assess hundreds of features of each person. Your father can have a funny conversation, your mother not so much, but she's patient and he isn't at all. While you feel attracted to both of them, you have a completely different assessment of each one. In such case, you do NOT  value two other persons equally.


What if three players are "the closest investigator"?

Question: In Eldritch Horror, when a monster causes the closest investigator to move one space closer to the monster, but more than one investigator is on the closest space, who moves?
Answer: The final decision is always down to the active investigator when you are deciding the nearest but two or more targets are an equivalent distance.
From the rules reference (page 9):

When determining the "nearest" space or token, find the space or
  token separated by the fewest number of interconnected paths.

If two or more spaces are tied for nearest, the active investigator
  chooses
Comment: I would add that when there is no active investigator (for example something happens in the mythos phase), then it's the lead investigator to choose.
Comment: I did read that, but I am talking about three investigators (read tokens) on the nearest space.  This rule does not answer that.  Hence the question.  Thanks for the response, though.
Comment: The rule specifically talks about spaces or tokens, only the bullet point says spaces. I would infer that the bullet point is generalising when it only says "space" and that the same applies for tokens.


Stubbing features in text classifications

Question: I'd like to classify short texts of chats to sentence types (i.e. an informational question, a request, a statement etc). In some of the texts there is extra information, like mentioning of another person. In case the mentioned person is known, we have extra metadata about him/her. For example, in the context of medical chats, a mentioned patient could have additional features of (sex, age). Assuming sex is a categorical feature (which I one-hot encode) and is age numerical, how should I treat instances where no one is mentioned? Simply padding with zeros seems wrong.
Answer: It's not clear how you classify texts to sentence types, but assuming you vectorize text in some of the standard ways (e.g. bag of words), you receive a number of features 'connected with words appearing in the text'. AFAI understand, after you discover a mention, you can extract extra features.
It's not clear for me to too what do you want to do with these extract features. If they are extra features for text classification than you have a classical case with missing values in categorial / numeric features. Look for 'imputation of missing features' - there is a lot about it. Out of standard ways to deal with it, I would recommend adding yet another feature indicating whether the information is missing or not, so e.g. when you don't have age, you put 1 to that column - apart from putting 0 to age or any value you impute (e.g. mean).
BTW these extra features needs to be properly included into classification algorithm, as they have different nature (e.g. range) than typical bag of words features. You may need to normalize them for example.
Comment: Thank you, one of the issues is that I don't know in advance how many people might be mentioned, and taking some max value seems an overkill. I'll read about feature imputation.


How to block the response of certain DHCP server

Question: There are multiple DHCP servers that run on our LAN, and some of them are unwanted. Can I configure my OS to reject certain responses so that I can get the correct one?
Answer: Unfortunately that's the wrong way to achieve this. DHCP is a protocol that works completly in broadcast. From the discovery, to the offer, to the request and the acknowledge; every single step happens over the broadcast address 255.255.255.255.
The DHCP server normally uses option 54 to identify himself (See RFC2132, Chapter 9.7). If you have a rouge DHCP server in your net, nothing stops him from identifying himself as your DHCP server with that option 54.
So, you can configure your client system to ignore other DHCP servers, but as you see that's only an ineffective solution.
If someone stuck a "rogue DHCP server" in your network, then you need to find out how/why and take necessary measures to ensure it doesn't happen again. Such a problem should be solved at layer 1 or 2, if possible.
One solution is called DHCP snooping. This is a mechanism where your switches are configured to determine where DHCP messages are allowed to come from. Your switches must support that.
Another solution is using VLANs. In a company for example, you can put every department or every floor in a separate VLAN. If now there is a rouge DHCP server only that VLAN is affected and you can encircle the rouge device very fast. Switches must of course support VLANs.
Comment: I am not the administrator of the network, so the only changes I can do is on my own system.
Comment: @SiyuanRen When using `dhclient` you can use the reject directive, see https://www.freebsd.org/cgi/man.cgi?query=dhclient.conf&sektion=5


Global proof of Serre duality

Question: Does anyone know of a global proof (involving no local argument) of Serre duality at the level of varieties or manifolds (as opposed to schemes).
Comment: Could you clarify what "no local argument" means?  Is the Hodge theorem a "local argument" because being harmonic is a local condition?
Answer: You might like the proof in section 5.3 of Voisin's book Hodge theory and complex algebraic geometry.
Answer: I thought I'd offer a high-tech alternative for certain varieties. If $X$ is smooth and projective over a field $k$ then Bondal and van den Bergh give a proof in Generators and representability of functors in commutative and noncommutative geometry that $D^b(\mathrm{Coh}X)$ is saturated which is a strong representability condition on cohomological/homological functors to the category of $k$ vector spaces. It follows immediately that $D^b(\mathrm{Coh}X)$ has a Serre functor by using the fact that $Hom(A,-)^*$ is representable for every bounded complex of coherent sheaves $A$.
Answer: Since a $\bar{\partial}$-Operator is an elliptic Operator, you can use elliptic theory in order to prove the Serre duality. In fact the Serre duality is a kind of corollary of the"fundamental theorem" (as I Know it). In fact, you do not need the Hodge theorem, since the Hodge theorem itself is a corollary of the theorem.
For a reference of this "fundamental theorem" (perhaps slightly reformulated) I would refer to one of the following:

Wells, Differential Analysis on Complex Manifolds;
Gilkey, Invariance Theory, the Heat Equation and the Atiyah Singer Index Theorem

(a complete proof for pseudodifferential operators)

Warner, Foundations of Differentiable Manifolds

(the theorem is included as an exercise on the last page

Kazdan, Lecture Notes on Applications of Partial Differential Equations to Some Problems in Differential Geometry (online available  here)

(Corollary 2.5, for a sketch of the proof)
Answer: I like the presentation from Analytic methods in algebraic geometry by Demailly. Here is the link: http://www-fourier.ujf-grenoble.fr/~demailly/manuscripts/eem2007.pdf.
Answer: Have you looked at the one in Griffiths and Harris?  That's at least rather different from the general nonsense one in Hartshorne.

Global proof of Serre duality


Does the FL1 train now go directly to Termini in Rome?

Question: The offical travel planner (also on google maps) it says that the FL1 train goes directly to Rome central station (Termini). But wikipedia page and other pages says it doesn't , which is correct?
Comment: A couple of months ago when I used it, FL1 didn't and you had to change, or you could take the more expensive Leonardo Express direct to Termini
Comment: Yes, that's what I am reading everywhere too. But it does not align very well with the offical travel planner...
Answer: Being the FL1 a regional train operated by Ferrovie dello Stato, I would trust their official FS site more than the ATAC journey planner (or Google for that matter). The FS page on the Airport train services says that the FL1 takes you from Fiumicino to most train stations within Rome. These are (ordered by closest distance from the airport):

Roma Trastevere
Roma Ostiense
Roma Tuscolana
Roma Tiburtina

Quoting from the linked FS page:

FL1 REGIONAL TRAIN to and From Rome/Fiumicino Airport
With trains departing every 15 minutes Trenitalia's FL1 regional train takes you from Leonardo da Vinci Airport to the main train stations in Rome (Trastevere, Ostiense, Tuscolana and Tiburtina).
The train also stops in many other important stations in Rome, and travels as far as Fara Sabina/Orte.

It would therefore seem that to date the FL1 train does not stop at Roma Termini. For more information here is a PDF with the full list of stops. Below is a map of the regional train network, courtesy of Wikimedia:


Adding an html action link to an Entity Framework Code First AddModelError string

Question: I am pretty new to programming so sorry if I'm being stupid, but I am writing an ASP.Net MVC3 application in which, if a particular exception is caught a message is displayed because of a composite key violation.
I can catch the exception but in the message I want to add an action link to edit the data that has failed the key violation test.
I can't work out how to use a link in following example. How can I make "HERE" an action link?
            catch (DataException)
            {
                if (duplicateKeyAttempt == true)
                {
                    ModelState.AddModelError("", "A delivery charge already exists for this combination of customer type and delivery method. " +
                        "Please check the information you have provided, this selection cannot be saved. " +
                        "If you want to edit the existing database entry, click HERE");
                }

Thanks...
Answer: Have you tried changing the Error to just output the raw HTML for the link like this:
if (duplicateKeyAttempt == true)
            {
                ModelState.AddModelError("", "A delivery charge already exists for this combination of customer type and delivery method. " +
                    "Please check the information you have provided, this selection cannot be saved. " +
                    "If you want to edit the existing database entry, click HERE");
            }

What have you tried so far?


Appfabric cache

Question: I am downloading content files(zip) from server to iPhone, directly by specifying the server path in the iPhone . Is there a way to cache the content in server to Appfabric and iPhone to read the content from Appfabric cache.Any help or pointer would really help me meet the project deliverables.
Answer: So if I'm understanding the question correctly (and do feel free to correct me if not), it boils down to 'can I get items cached in AppFabric directly onto an iPhone'.
Right now, the only client libraries for AppFabric are for .NET applications (and I don't see much likelihood of Microsoft producing any in Objective-C either :-P ). Also bear in mind that Windows Server Appfabric is designed to sit behind the firewall, not to be directly accessible from the Internet (although I'm reasonably sure you could get round this with a VPN client). So on the surface, the answer is 'no, you can't'. But you could put a website or webservice in front of AppFabric that returns items from the cache, and call that from the iPhone - that's probably your best bet.
Answer: Yoy will have to create a web service/application that hosts those files for you in appfabric and get served to the iphone over TCP/IP. Most likely you'll need win servers for doing that. If what you have is Linux, take a look at Memcahced.

Appfabric cache


Is there a word we can use to refer to big clusters of clouds?

Question: Is there a word we can use to refer to big clusters of clouds, attached or unattached? I am thinking there might be a word, but I've never really heard of words related to cloud being used in any book I've ever read. I keep seeing words related to a type of clouds, but not related to a group or cluster.
Comment: [What is the collective noun for "clouds"?](https://english.stackexchange.com/q/44214/291924).
Answer: There are many choices.
English corpora
If you search there with the phrases
a NOUN of clouds  or
the NOUN of clouds
you will see many options (ranked by frequency).
These are a few from the first page: mass, sea, line, blanket, layer, canopy et al.
Answer: Jack's answer is good (and useful for poets), but the most idiomatic noun for a mass of clouds is bank.
The OED (Oxford English Dictionary) includes a sub-entry for cloud-bank, citing one J. Hodgson (1858): "A cloud-bank that seemed to rest on the sea."


What security risks do you face when connecting to a server via RDP?

Question: What security risks do you face when connecting to an (possibly foreign) RDP server? Opening an unsigned RDP file triggers the following warning:

RDP is a one way street, right?
Comment: Did you check this answer https://security.stackexchange.com/questions/38539/why-would-a-remote-desktop-connection-harm-my-pc
Answer: If the server's identity cannot be trusted, it is possible that you are subject to a man-in-the-middle attack. If that happens, an attacker can potentially read and/or alter your RDP traffic in either or both directions.
Having a MitM on RDP is just as bad as dealing with one on a web session, if not worse. Anything you send to the remote system - keystrokes, mouse activity, file/clipboard transfers, etc. - can be monitored and recorded by the attacker. Additionally, the same can also be altered by the attacker. Traffic coming to you is just as vulnerable. The attacker can see and hear all of the output from the remote system, as well as possibly alter it in transit. They could use this to inject malicious payloads into file/clipboard downloads or take over the session. Any local resources you share (e.g.: printers, local/networked drives, etc.) are put at risk as well.
That being said, most of these warnings are probably benign. The most common reason for seeing this is because the system is using a self-signed SSL certificate instead of one from a trusted Certificate Authority. This is the default configuration for all Windows systems, and usually is not changed except in very security-conscious business environments.
If you want to be sure whether you can trust a self-signed certificate, you need to check the certificate on the system locally first. Note the certificate's fingerprint while logged in locally, then compare it to the fingerprint of the certificate presented over RDP when you try to connect.


How to use group by, max of a column and also getting other columns of the model from a Django queryset?

Question: I have a model that looks like this
class Documents(models.Model):
    id = models.AutoField(primary_key=True, editable=False)
    uid = models.CharField(max_length=64)
    version = models.IntegerField()
    reviewed_dtm = models.DateTimeField(null=True)
    timestamp = models.DateTimeField(auto_add_now=True)
    document = models.FileField()

I want the average time difference between the timestamps for the maximum version and the minimum number for every uid. I basically want to know the average time it takes for a document to be reviewed by a user since its creation. Being reviewed is optional, if a user finds the document to be good then marks it as reviewed, or else sends it for the new version. Then another record is made for the uid with an updated version.
Answer: I wrote the ORM query for it. Here it is:
Documents.objects.values('uid').annotate(difference = Max('reviewed_dtm')-Min('timestamp')).aggregate(Avg('difference'))
Answer: it looks like you are looking for Window function
If you are not familiar with it, first of all, read how to use it in pure sql to understand this concept
Comment: Yes, I want the ORM query for it. Thanks


SSD "healthcheck"?

Question: Is there a program for linux to check the health an SSD drive?
Comment: Are you meaning you want to write a program like this, or you're looking to download and use?
Answer: The standard way to do diagnostics for hard drives was always smartctl. I guess the same interface should work for SSD... but I've got no experiences with SSD yet.
Answer: SSD Life is a good software, but for Windows only :(
As said liori above, you can use any SMART control software and look for attribute value, what corresponds to drive health. For example, for Intel SSDs it's a E9 - media wearout indicator, it's value is a drive health (100 = 100%).
Answer: You can try new software - SSDlife
Freeware version basic enough and support all major SSD drives and controllers.
Comment: This answer is not helpful at all! The linked site gives a dubious impression; besides it only offers software for _Windows_.

SSD "healthcheck"?


sanding old plaster wall texture to prepare for mudding

Question: Should I sand/grind old plaster texture before skim-coating?  If so, what is the best tool to use? The goal is to prepare for new smooth walls.
Answer: I assume you have a textured surface.  If so, yes sanding the peaks down a bit will help later on with the skim coat, because less skim coat will be required to fill in the uneven spots.
But there are things to consider.

Plaster dust gets everywhere, so sanding creates a big mess
Plaster is very hard, so it is hard or harder to sand that straight mud or joint compound
Plaster may contain asbestos if it is old, so you might want to test first before sanding

I would start with 120 grit paper and then move to 220 grit for finishing  Since plaster is hard, if you are not getting anywhere with the 120 , move to a 60 or 80 grit if necessary.
For sections that stick out the most, you may be able to scrape them off as opposed to sanding.
A power sander will be quicker than manunaly sanding with a standard block or pole  drywall sander.  I know some of the power sanders for drywall have vacuum attachments which may be wise to rent one to keep the dust down.
Also, with this type of job definately wear mask and tape off other areas of the house prior to sanding.  I usually try to leave windows open for fresh air because it gets really dusty.
Comment: it would help. But I'm pretty sure a pro plasterer would just put up mesh and scratch and skim coat over it all. Also he should know what kind of plaster he's got (lime or gypsum). Since the wall is covered in layers of paint anyway, I would definitely use an adhesive like weld crete first, otherwise you may find your beautiful skim coat crumbling off in a few years.


how to approach this sort of probability problem

Question: Question 2: Suppose a new Internet company Mumble.com was to require
all employees to take a drug test. Mumble.com can aord only the inexpensive
drug test { the one with a 5% false positive and a 10% false negative
rate. (That means that ve percent of those who are not using drugs will incorrectly
test positive, and ten percent of those who are actually using drugs
will test negative.) Suppose that 10% of those who work for Mumble.com are
using the drugs for which Mumble.com is checking. An employee is chosen
at random.
(a) (3 marks). What is the probability the employee both uses drugs and
tests positive?
(b) (2 marks). What is the probability the employee does not use drugs
but tests positive anyway?
(c) (2 marks). What is the probability the employee tests positive?
(d) (2 marks). If the employee has tested positive, what is the probability
he or she uses drugs?
Comment: Might be helpful: http://people.hofstra.edu/Stefan_Waner/RealWorld/tutorialsf3/unit6_6.html
Answer: (a) The probability she uses drugs is $0.1$. Given she uses drugs, the probability she tests positive is $0.9$. Multiply.
(b) Same idea, a little simpler.
(c) Add the answers to (a) and (b).
(d) Let $D$ be the event she uses drugs, and $P$ be the event she tests positive. We want $\Pr(D|P)$. By the defining formula for conditional probability, we have
$$\Pr(D|P)=\frac{\Pr(D\cap P)}{\Pr(P)}.$$
The numerator has been calculated in (a), and the denominator in (c).
Answer: Hint: This question uses both conditional probability and Bayes' Rule.
Also, please show us what work you have done in your attempt to solve this problem. We are not here to answer your homework questions without any effort on your part. Thanks.


Where can I get easy double kills with the Fusion Rifle?

Question: I have a Vanguard bounty ("Overcharge") to "kill 2 enemies at once with a Fusion Rifle, 20 times". I've tried cornering enemies to get the double kill, but it doesn't seem to count. Is there an area or technique that is most efficient for completing this bounty?
Answer: The temples under the Moon are a good place to earn this Bounty. Play your favorite Story mission or Strike and you will inevitably be attacked by swarms of Thralls who love to charge you head-on, in single file. They also have low health stats, so the fusion rifle is more than capable of tearing through them and getting three or four dead in one burst. I doubt you get additional credit for killing more than 2 enemies at once, though.
Pocket Infinite is a fusion rifle that fires like an automatic. It can make Fusion Rifle multikills much easier to acquire on any location.
Comment: You don't get credit for more than 2 in one shot. The thrall swarms on the moon is where I did most of mine, it really is the best place.
Comment: Any good levels in particular?
Comment: I found that Shanks love to fly close together, tend to not run away, and stay relatively motionless if you'd prefer to play on Earth.
Answer: In this video, it's described that The Last Array (Earth) is a pretty good place to get this bounty.
Answer: Hive Thralls are your best bet at nailing this one quickly.
Most strikes featuring hive will have tons of them,  but I find the best ones to try (for quick repeatability) are actually either the fist of Crota mission, when omnigul spawns droves of them in,  or the first story mission on the moon,  once the hive gates open,  there's plenty of them to massacre.
if you just want it done quickly,  FR the Thralls,  and let the Knights kill you.  The kills still count towards your bounty,  and you get put back to the last check point (the gates opening ) so you can do it again without having to re-do the whole mission from the start.


Why is it possible to eliminate this branch with alpha-beta pruning?

Question: Can someone explain to me why it is possible to eliminate the rest of the middle branch in this image for alpha-beta pruning? I am confused because it seems the only information you know is that Helen would pick at least a 2 at the top (considering if we iterate from left to right in DFS), and Stavros would absolutely not pick anything above 7. This leaves 5 possible numbers that the rest of the branch could take on that Helen could potentially end up picking, but can't because we've eliminated those possibilities via pruning.
Comment: Meanwhile, you may want to have a look at these notes [http://web.cs.ucla.edu/~rosen/161/notes/alphabeta.html](http://web.cs.ucla.edu/~rosen/161/notes/alphabeta.html). In my opinion, they provide a good explanation of the $\alpha-\beta$ pruning algorithm. I may provide an answer later, if nobody does it.
Answer: You can't prune the nodes that are cross out if we search from left-to-right in the tree using alpha-beta pruning. To do this analysis we can pretend the right branch of the tree doesn't exist. (Branch C from the root.)
In the left branch (A) of the root Helen will get 2 or more.
In the middle branch (B) from the root after going down the left, Stavros will get 7 or less.
Now, we can ask what happens if we put different values for the crossed out branches. If putting different values doesn't change the value at the root, then pruning is correct.
Suppose that after the 7 on branch A at the second level we make the value of branch B to be -10. In this case the value of the second branch will be -10, and Helen will prefer the first branch at the root.
Suppose that after the 7 on branch A at the second level we make the value of branch B to be 100. In this case the value of the second branch will be 7, and Helen will prefer this branch.
Thus, the value of the crossed off nodes matters, and they cannot be pruned.
You may find this tool useful for exploring alpha-beta on binary trees:
https://movingai.com/ab/