What exactly is a SIM card?

Question: Does a SIM card consist of only Flash memory or is there a microprocessor inside as well?
Comment: Not sure about SIM, but this chip in a credit card has a microprocessor that can perform encryption and decryption iperations.
Answer: There is a small microcontroller inside.
Most SIM cards these days can be programmed in Java and follow the JavaCard / GlobalPlatform standard. You won't get the keys to install your own applications though.
Comment: @VishalSharma SIM cards are secure devices, therefore the information about architecture and specs aren't available to the public. You probably don't want average joe mess with critical infrastructure like the cell phone network. That's why you won't find anything about the internals. All the information how to program them, what protocol they speak etc. is standarized and public information though.
Comment: SIM cards are no different in many ways to Smartcard and similar in some ways to  USB storage or SDCards.... they all have a small onboard processor that implements the interface protocol. In the case of SIM/Smartcards, the processor is very secure. This might help you: http://www.technoburst.net/search?q=SIM+cards+tutorial&x=0&y=0
Comment: The document for the SLE 88CNFX6600P (a random old SIM chip) gives an architecture overview: 32-bit RISC with proprietary instruction set, 660k EEPROM, encrypted 32k RAM, hardware crypto engine and random number generator, security sensors to detect glitching, power management, 33MHz internal clock, memory management with hardware firewalls, etc. Some other SIM chips are ARM Cortex M0 based. https://4donline.ihs.com/images/VipMasterIC/IC/INFN/INFNS15319/INFNS15319-1.pdf
Comment: I couldn't find any online resource/link, where it's explicitly mentioned that the SIM card contains microprocessor/microcontroller. Why do you think we don't have info/details of SIM card about the microprocessor, their architecture, specs etc. The same info is available for the smartphones though.
Answer: Even "simple" memory cards like SD, CF, MMC... must have processors inside them because you don't access the memory chips directly. Each memory chip is different in number of pins, address bus width, data bus width, access protocol... so the processor will create a common interface for communicating with external devices.
In case of SIM card there must be a microcontroller in the SIM card to process data, because the purpose of the SIM is to prevent the authentication key from being read. The phone never knows what key the SIM is currently holding. Only the mobile network operator and the SIM know that.
The phone just gives some data to the SIM and the SIM's processor will return back the encrypted data based on the key after some cryptography algorithm. That encrypted data will be sent back to the network operator, who will use the same algorithm to generate the encrypted data from the key in their database. If the two piece of data match, the authentication ends successfully.
More information about the authentication process can be found here
Comment: This is interesting. You are saying that an SD card has also got a microprocessor!
Comment: yes. SD protocol has a lot of commands that may be easier to implement in software. Moreover memory access is often in parallel and you need to convert to serial to send via that limited number of pins

What exactly is a SIM card?


Can I use a guitar amp with an electric bass?

Question: I have a passive bass and a Fender Frontman 15g guitar amp. Is it safe to use the amp with my bass?
Answer: The amp has 15W and an 8" speaker.  Problem with that is that an 8" speaker cannot move a lot of air before it has to turn around.  Meaning that it may be overtaxed with reproducing low notes.
Most guitar amps are comparatively robust against overdriving since that's what people tend to do a lot.  If most of your notes are low notes, the speaker may get a lot of power while moving comparatively slow, meaning that it may not get rid of the accumulating heat as much as it is designed for.
So probably the most strenuous you can be for a single-speaker guitar amp with a bass is by playing consistently clean low notes near to clipping volume.  While possibly cranking up the bass tone control to get more of a punch in your stomach area.
If instead you are aiming for a funky, treble rich sound, possibly with distortion and while leaving the bass tone control alone and forget about the kind of low sound you feel more than hear, I doubt that you'll be damaging anything.
You just might end up more underwhelmed with the amp's power than you would with a guitar.
Answer: As long as you're not expecting it to sound like a loud bass amp., yes, it'll be fine. Obviously you're not going to take it to gigs, but certainly for home or garage practice it'll be fine. Just make sure it doesn't get loud enough to distort - as at that point, it may well not be the amp's inbuilt distortion, but the speaker starting to break up! I'd be looking to add an extension speaker to it - 10" minimum, and watch the impedance, as that will improve the sound no end.
Comment: Unless the extension speaker is very cheap or free, you might as well look for a cheap used bass combo instead. It'll sound better and the controls will be more suited to bass.


Composer.lock in library

Question: I have an application using Composer here at work, and we commit the composer.lock file so our dev and prod are the same.  But when creating a library that is installed by composer, should I commit the composer.lock file for the library as well?  Or will that cause problems for our internal repo or for composer itself?
Answer: It won't cause any issue because the composer.lock is only used when you actually run composer install within the library's root directory. When it is installed as a dependency the dependencies' lock files are never taken into account.
That said, for libraries it indeed does not really make sense to commit a lock file, so feel free to .gitignore it. We just say to always commit it because that is what 99% of the people should do. If some library authors know better and ignore it in their libs that's fine, but it does not really matter either way.
Comment: Library maintainers will "run composer install within the library's root directory" when they're working on the library itself. They often find it useful to have the same version of e.g. phpcs or phpunit installed (require-dev more often than not, but still useful to have locked).

Maybe you could clarify why it "does not really make sense"? I can only think of situations where there is literally nothing being locked.
Answer: It's worth putting the composer.lock in a library for the same reason that you would put it in deployable projects; to allow you develop and test the library against exactly the same  dependencies that were used in it's development.
This would be useful for your automated testing of libraries, as well as helping to quickly identify whether bugs in the library are caused either by a an actual bug in the library itself, or a bug/changed behaviour in one of it's dependencies. Or to put it more colloquially it help avoids the 'works for me' problem.
As Seldaek said, the composer.lock file for a library is not passed up to be used by a project that merely requires that library. It is only used when you are running composer in the root of the library.
So with a small benefit of adding it, and with no downside, I'd recommend adding it.
Comment: I suppose it is useful when you want to have reproducible builds in your library.

Composer.lock in library


Lightweight Grid saving to file

Question: I'm trying to launching my first jobs on LightWeight Grid using ParallelDo. I have 10000 jobs, each of which returns a 1M output, which I would like saved to a file on the head machine, one file per run. My basic challenge is that Mathematica saves by default to the slave node.
I have many solutions, none of which very good:
1-Save in a temp directory on slave, then collect the files at the end of the job. My best option so far, but not very elegant. I pass the file names as variables, save those to a file, and write a shell script to copy the files to the local machine.
2-Pass output as variables to the head node. The problem is that this fills up the memory of the master machine and saves nothing until the 10000 jobs are running. I can break the job into chunks by hand, but that's not efficient.
Is there a way to either:
-Pass the output as a stream-like object that can be saved on the fly, rather than at the end of the computation,
-Save efficiently from the slave to the master computer.
-easily collect all the output from the local temp directories?
Comment: Hi, welcome to Mathematica.SE, please consider taking the [tour](http://mathematica.stackexchange.com/tour) so you learn the basics of the site. Once you gain enough reputation by making [good questions](http://mathematica.stackexchange.com/help/how-to-ask) you will be able to vote up and down both questions and answers. When you see good ones, please vote them up by clicking the grey triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge. As you receive help, try to give it too, by *answering questions* in your area of expertise.
Answer: This isn't a perfect solution either, but it's an improvement on your solution 2:
Use ParallelSubmit and WaitNext for parallelization.  Documentation is here and here.  With this method it is not necessary to collect all results to the main kernel first, and export them only afterwards.  You'll be able to collect one result, save it, collect the next, save that, etc.
Also, be aware of this bug which can cause the main kernel to run out of memory.  See the workaround at that link.

Lightweight Grid saving to file


XTS-AES key management

Question: XTS-AES uses two keys $(k_1, k_2)$, which are obtained from a concatenated key $k$. Does this key $k$ remain same for the whole disk or changes per sector?
Comment: I can't write a full answer right now: $k$ remains the same for the whole disk.
Answer: To answer the question we first need to take a quick look at how XTS encrypts data:
$$C=E_{k_1}(P\oplus(E_{k_2}(n)\otimes\alpha^i))\oplus(E_{k_2}(n)\otimes\alpha^i)$$
With $\oplus$ denoting bitwise XOR, $n$ denoting the sector index, $i$ denoting the block index within the sector. $\alpha$ is a polynomial in the $GF(2^{128})$ and is exponentiated appropriately and multiplied ($\otimes$) with the encrypted sector index.
As you can see you don't need to alter either the key $k_1$ or $k_2$ for each sector as the indices will introduce a unique whitening value for each block.
Comment: won't the behavior be  similar to two-time-pad, which is considered bad for cryptography?
Comment: @Baruntar, no as 1) you don't want to achieve perfect secrecy here (which two-time-pad can't provide) and 2) this is basically ECB mode (also bad) but with different whitening for each block (making it good).
Comment: but still the whitening of each block remains same over a prolonged period of time. Also you mentioned the aim was not to attain perfect secrecy. Can you provide reasons for the argument? I thought purpose of disk encryption would be to provide secrecy.
Comment: @Baruntar, secrecy? yes. *Perfect* Secrecy? no. Perfect secrecy means you can't learn anything about the plaintext except from what you already know even with infinite computing power. "Normal" secrecy restricts this to "reasonable" (polynomially bounded) power. And yes, the whitening will stay the same over time but this only tells you the block has changed and not the value it has changed to. XTS is not perfect (it's unauthenticated and lacks randomization) but it's the best we have at the moment for FDE.

XTS-AES key management


[Meta] Did our site make the cut for StackExchange 2.0?

Question: I'm going to keep posting questions and answers here no matter what, but are we defined as an "Active" site or not under StackExchange's new rules?
Answer: We are not defined as "active" in terms of having 1 year before moving to the new system. So this site, at the latest, will be moved over to 2.0 within 3 months.
However, Taylor and I are excited for this, and might even be willing to migrate over even sooner, if possible.
Considering how many IT / developer related people also homebrew, we both feel that BrewAdvice will have no issue staying alive when it comes to a StackOverflow.com vote. I think we have almost a dozen active users on here who write code or do something in that field.
I think Taylor is going to contact Rich or someone else at SE to discuss this in further.
We'll make sure this site stays around even if we don't make the cut.
Please, continue to ask more questions as you have them, both about beer and about BrewAdvice!
Comment: I have been wondering how many visitors there really are, because things have seemed to slow down over the past 4-8weeks.
Comment: I can give you the actual analytics if you want. But ya, it has slowed down a bit. I had some extra google ad word credits from GoDaddy, so I had those pushing traffic for a little bit too.
Comment: Dashboard 1/1/10 - 4/14/10 http://skitch.com/hookedonwinter/n6hn1/dashboard-google-analytics
Comment: Dashboard 1/1/10 - 4/14/10 - overall stats - http://skitch.com/hookedonwinter/n6hn1/dashboard-google-analytics
Comment: General Traffic Sources 1/1/10 - 4/14/10 - http://skitch.com/hookedonwinter/n6hn2/traffic-sources-overview-google-analytics
Comment: If you want to see any other stats, let me know
Comment: Thanks for the info.
Comment: @brewchez:
Sorry, but I think I joined about 4-8 weeks ago.  Did I forget to brush my teeth or something? :)
Answer: Just FYI (and not sure where else to put it), Stack Exchange launched their site launching site (repeat words much PJ?) at area51.stackexchange.com. The beer community site is being discussed here: http://area51.stackexchange.com/proposals/1619/homebrewing-beer-wine-etc
Please go give your input over there. I'd love for this community to help shape the future of this site.
Comment: I registered and started adding questions/commenting - but, what is this exactly? If this proposal is accepted, what are the ramifications for brewadvice?


Voltage Circuit Switch with BJT

Question: I have Found One Circuit Which acts as Switch to Pass 15NV (15 Negative Voltage) to Opamps Negative (-VCC) Supply But I am unable to understand its working . Why Two NPN are used in this Circuit ? What is the Purpose of Capacitor C1 ? R3 is used to limit current or has different purpose ?
Please Help me understand the Working of this Circuit and its actual Usage .
Comment: The circuit topology is pretty standard, when \$Q_1\$ is operating in active mode. It sets a collector current that drives \$R_2\$. However, in this case \$Q_1\$ is saturated and its collector acts more like a voltage source than a current source. Which might make good sense if the topside of \$R_1\$ is how you enable/disable this. But you don't explain much of the context. So I can't really tell you much more. \
Comment: @jonk R2 is probably just raises the output to bias it on.
Comment: @jonk The Purpose of this circuit is to pass the -15NV which is generated From Somewhere else and give it to Opamps Negative VCC Supply. Please Check my understanding . When The Base of Q1 is less nagative ( approximately  by 0.7) than emitter then  Current will start flowing from collector to emitter . due to High Resistance of R2 there will Very Less Collector current so all Emitter Voltage appear across the R2.so  Q1 acts like switch here.  the purpose of R1 is just to give bias voltage to  Q1.
Comment: @Rohan I'm not sure I understand your writing. (My apologies.) I tried. But I'm just not parsing it well. The ***only*** question I have is whether or not there is a control signal that is used to ***enable*** and ***disable*** this supply. If so, it would likely be one that exists (unshown) at one end of \$R_1\$. Is there a control signal to enable/disable this supply to the opamp? Or not?
Answer: It looks to be a 12mA 15mA short circuit protection current limiter on Vee
It acts as a Voltage switch that limits current.
0.6V/47 ohms = 12mA
err 12.77

actually  up to 15mA at cold temp  as 0.6 rises 4mV/'C to 0.7V at +25'C rise
0.7/47=15mA

which is a typical BJT Op Amp current limit, since the Q2 base current is very low
~15V/12k /hFE=Ib the threshold is only 0.6V at room temp.

For more examples of this limiter, see this for a 12V 1A Zener regulator limited to 1.3A Short circuit output
Comment: Can You Please Elaborate its Current Limiting Action. 15mA will Flow through  transistor  Q2 base ?  you want say the base current of Q1 is very Low ? what happens  if more than 15 mA flows ?
Comment: Q2 Vbe sees 0.6V and pulls down Q1 Vb to limit current.  Current gain in the loop is hFE1*hFE2

Voltage Circuit Switch with BJT


Upload and Process File ASP.NET MVC 3

Question: I'm new to ASP.NET and MVC3 and I'm trying to figure out how to upload a file and process its contents and then display the results in a view.
I can successfully upload a file using the following view code:
@using (Html.BeginForm("Index", "Home", FormMethod.Post, new {
id="UploadForm",
enctype = "multipart/form-data"})){
<input type="file" name="file" id="Upload" size="60" />
<input type="submit" value="Submit" id="submitID" /> }

...And the following controller code:
public ActionResult Index(HttpPostedFile file) {
if (file != null && file.ContentLength > 0) {
var filename = Path.GetFileName(file.FileName);
var path = Path.Combine(Server.MapPath("~/REPO"), fileName);
file.SaveAs(path); }
return RedirectToAction("Index"); }

What I can't quite figure out is how to proceed after I've uploaded the file:  I want to execute a server-side code to read the file contents and then display the results on the index view.
So this is what I want to do:

Redirect to some process (controller action)
Pass the file name in a string to the action
Read the file using the server-side program to produce an output (this part is already coded in C# and outputs a string from a string input)
Pass that string back to the index view controller to display on the page

What do I do?  Please be explicit with an answer, and not assume too much, because as I said, I am relatively new to ASP.NET and MVC (~2 weeks).  Thanks for your help!
Answer: public ActionResult Index(HttpPostedFile file)
    {
        if (file != null && file.ContentLength > 0)
        {
            var filename = Path.GetFileName(file.FileName);
            var path = Path.Combine(Server.MapPath("~/REPO"), fileName);
            file.SaveAs(path);

            string result = DoStuffWithFile(file);

            ViewBag.FileResult = result;

        }
        return View();
    }

Then in the view use @ViewBag.FileResult to get the string.

Upload and Process File ASP.NET MVC 3


Cycles rendering mode crashes the entire program AMD OpenCL

Question: I never had this problem before, I recently came back to Blender and I'm doing the Donut series by Andrew Price, everything was working fine and I got midway but from one day to another, the entire program freezes and crashes or bugs out when I switch to render view mode in viewport or rendering with f12. I use a AMD RX 570 8gb, as I said everything worked fine, I already tried different drivers for my card, older and newer, I play a lot of games and there aren't problems there. I already switched to 2.91 version of Blender, and 2.9, Idk what else to do, I cleanly uninstalled my graphic drivers with DDU even, but it's the same, the program now gives an error with 2.91 tho, it says: "Split kernel error: failed to load kernel_indirect_background". The program is not frozen but I can only see the orange outlines of my objects if selected, there's nothing else in the viewport. Please help me, I'm really eager to learn to use this program again, and it's my favorite one tbh. I use Windows 10 Pro latest update.
Comment: If it was working before, then go back to the version that worked. There might be a conflict with that specific GPU (AMD's have a long history of problems with blender).
Comment: I mean it's still installed, the version is 2.9, I just downloaded the 2.91 as a portable version and I opened the same file in there, so it gave me the Split Kernel error. Version 2.9.0 doesnt give an error but the rendering is all glitched, there's straight lines in the inferior left part, and blue and red pixels appeared which weren't there before, I followed everything like the tutorial says, I didn't change anything as far as I checked.
Answer: Posted this in an AMD forum Users Post:
Re: In 2021,Why AMD GPU Still Sucks On Cycles?!
I think I might have found a so-called hack to get the 'Indirect_Background' one to work.

Start with initial default cube. Mainly so that Blender will recover faster.
Add a HDRI (don't really know if you have to).
Switch from 'Solid' view to 'Mat Preview' then switch to 'Render' view. Now I think it does start to hang, but immediately switch back to 'Mat View' and wait for it to clear its self up. Then switch back to 'Render' view.
Hit F10 while still in 'Viewport' (may not have to do this, but was in 'Mat Preview').
Go to Render tab and watch the magic happen (hopefully).

I don't think I've forgotten anything. You can then open another file and everything should still work. Even on start up.
*** Updated to Adrenaline 21.4.1, repeated what's above and it still works ***
Comment: Fantastic, going to mat preview THEN render worked, thank you so much
Comment: I'm so happy it worked for you (really).


Can a CSPRNG, seeded with a key, be used to generate a byte sequence as long as the plaintext to XOR it with that?

Question: Given a "safe" (meaning: brute-force is your only shot) cryptographically strong PRNG, wouldn't it be safe to encrypt data using the CSPRNG to create a key as long as the data and then encrypt the data by XORing it with the key?
Comment: We call that a (synchronous) stream cipher.
Answer: Yes it would.
As CodesinChaos reminded us in his comment:

We call that a (synchronous) stream cipher.

Look up RC4 and A5/1, two of the most statistically popular ciphers in the universe.  Also compare to a correctly generated one time pad.  Not a lot else to say at this point.
Answer: The only secure-proven encryption scheme is the one-time-pad. That uses a key of plaintext-length for XOR-encryption once, else it is broken. If your CS-PRNG is not breakable, in sence of any attacker is able to win the predictable game, it is close to being a OTP.
Now think about you would like to encrypt a branch of Wikipedia. How would you like to (1) store and (2) transport the key secure? How would you make sure that no key is used twice?


Determining the conjugacy classes of a wreath product $G \wr S_n$

Question: If $G$ is a finite group and its conjugacy classes are known, can the conjugacy classes of the wreath product $G \wr S_n \cong G^n \rtimes S_n$ be determined?
Comment: Yes, this is well known.  It is described in detail in James and Kerber's book on the representation theory of symmetric groups.
Comment: Did you mean $G\wr S_n\cong G^n\rtimes S_n$?
Comment: In that case Chris, the notation is the wrong way round, and Alex's is what you meant ( and I think the group dealt with in James-Kerber as mentioned by Christian).
Comment: Alex: I mean for $S_n$ to be acting on $n$ copies of $G$, in the natural way. Have I gotten the notation the wrong way round?
Answer: This is indeed handled in Section 4.2 of James and Kerber's book on Representations of the Symmetric group.
We also considered this problem in Section 2 our paper describing a computer algorithm for computing conjugacy class representatives in permutation groups.
J. Cannon and D. Holt, Computing conjugacy class representatives in permutation groups,
J. Algebra 300 (2006), 213--222.
I can cut and paste the main bit of theory you need. The problem easily reduces to finding those classes that map onto a specific element of $S_n$.
Let $A$ be any group, let $P$ be a permutation group acting
on the set $\{ 1\ldots d\}$, and let $W := A \wr P$.
Then $W$ is a semidirect product of $A^d$ by $P$, and elements
of $W$ have the form $(g,x)$ with $g \in P$, $x \in A^d$, and
$x = (x_1,\ldots,x_d)$ with $x_i \in A$. In general, for $x \in A^d$,
we denote the $i$-th component of $x$ by $x_i$.
The action of $P$ on $A^d$ in $W$ is given by:
$$(g,1)^{-1}(1,(x_1,\ldots,x_d))(g,1) = (1,(x_{1^{g^{-1}}},\ldots,
x_{d^{g^{-1}}})).$$
Hence, for $g \in P$, $x,z\in  A^d$, we have
\begin{equation}\label{conjeqn}
(1,z)^{-1}(g,x)(1,z) = (g,y), \ \mathrm{where}\
y_i = z^{-1}_{i^{g^{-1}}}x_iz_i \ \mathrm{for}\  1 \le i \le d.
\end{equation}
$\textbf{Theorem}$   With the above notation,
let $x^{(1)},\ldots,x^{(k)}$ be representatives of the conjugacy classes of $A$.
Fix an element $g \in P$, and let $r_1,r_2,\ldots,r_s$ be representatives of
the cycles of $g$ in its action on $\{ 1\ldots d\}$. Then
$$
R := \{\,(g,x) \mid  x_i = 1 \ \mathrm{for}\  i \not\in \{r_1,\ldots,r_s\},\,
           x_i \in \{x^{(1)},\ldots,x^{(k)}\}\ \mathrm{for}\
i \in \{r_1,\ldots,r_s\}\,\}
$$
is a set of representatives of the $A^d$-classes of elements of $W$
of the form $(g,x)$ for $x \in A^d$.
The size of the $A^d$-class $R_{gx}$ containing $(g,x)$ is the product of the sizes of the classes of the $x_i$ in $A$ with $i \in \{r_1,\ldots,r_d\}$ with the lengths of the cycles of $g$ that contain $r_1,\ldots,r_d$.
The above describes the $A^d$-classes of $W$; i.e. the orbits under conjugation by the subgroup $A^d$ of $W$. To get the classes of $W$ itself, first of all we only consider those $R_{gx}$ as $g$ ranges over a set of class representatives of $P$. Then, for each such $g \in W$, the $A^d$-class representatives $R_{gx}$  are fused under the action of $C_P(g)$. This action is the same as the action of $C_P(g)$ on the cycles of $g$, so is easy to calculate.
Then the size of a $W$-class $R_{gx}$ is the product of the size of the class of $g$ in $P$ with the sum of the the sizes of the $A^d$-classes $R_{gx'}$ that lie in the orbit under the action of $C_P(g)$.
Comment: My answer was incomplete because it only described the $A^d$-classes. Calculating the $G$-classes from thsi information is not difficult - I have added some further explanation.
Comment: Thank you Derek, I see how an element $(g, x)$ is conjugate to something in the set $R$ you define. If I write
$$R_g := \{\,(g,x) \mid  x_i = 1 \ \mathrm{for}\  i \not\in \{r_1,\ldots,r_s\},\,
           x_i \in \{x^{(1)},\ldots,x^{(k)}\}\ \mathrm{for}\
i \in \{r_1,\ldots,r_s\}\,\}$$
is there a way to describe a subset of $$\bigcup_{g \in G}R_g$$ which contains only one representative from each conjugacy class?

Also is there a way to determine how many elements are in a each conjugacy class?
Comment: I think I get the idea of how it works now but I'm not sure what $G$ is in the second last paragraph of your updated answer, which is confusing me. In one place I'm interpreting that $A^d$ is a subgroup of $G$ but in another $g \in G$ where I thought $g$ is an element of $P$.
Comment: Sorry $G$ should be $W$. I don't have a $G$. I have $W = A^d \rtimes P$. Of course $P=S_n$ in your question.


What is this creeper that may be giving me a rash?

Question: I'm trying to identify which plant in my late mother-in-law's garden is giving me a rash. I think it might be this creeper that seems to grow both horizontally & vertically. The location is eastern Virginia, USA. Any help you can offer regarding identification would be a great help.
Comment: Lloyd, do you have other allergies?  Definitely need pictures.  I used to have this gorgeous golden hops that I couldn't touch much...thank you for the picture.  Is the other plant Mondo grass or Liriope?  Have you seen any flowers on this ODD PINATE leaved plant?  Be back soon...
Comment: no, no plant allergies that i'm aware of. i didn't grow up in this part of the world so everything here is outside my already extremely limited knowledge base. no flowers on the odd pinate leaved plant. as for the other plant, i'm sorry i have no idea what it is but there's a lot of what appear to be wild strawberries in the same bed.
Comment: I found the plant I am fairly sure is your problem...Trumpet Creeper and it affects everyone that touches it!  Wait until you see the pictures of this plant in flower!  Just wear a rubberized hazmat suit whilst in the garden, grins!  Make sure you take benedryl (sp) when you react like this.  Otherwise you keep getting more and more sensitized.  Just call me Doc Stormy.  I just went through an insect bite where I didn't take benedryl (sp) and I was pretty miserable for 5 days.  And I am not a sensitive person.  Of course ask your doctor...gotta put that in!
Comment: Wear gloves and long sleeves.  If you feel any burning or itching just quit and hire someone else to do this work.  Take benedryl!  Discuss this with your doctor of course first.
Comment: @stormy - it doesn't affect anyone  who touches it - I handle this regularly without any problem at all. But its the sap that can cause itching, though it should pass quickly if its this - if its an ongoing rash and itching, might be something else
Comment: Guess everyone is different.  I didn't know this either until I looked it up and it most certainly is an irritant for lots of people.  Definitely a good thing to put out there that his rash might not be from this plant.  But this plant most certainly causes skin rash and the itchies.  I've become more sensitized not less with age.  I hate worrying about allergies but I got stung at least 47 times by bald faced hornets because they pulled 47 stingers out of my skin.  Luckily I went to town to find a clinic cause I did get anaphylactic shock.  That was not a good day!
Answer: This is Campsis radicans or Trumpet creeper.  Most definitely your problem.  Causes lots of rashes and itching!  Very very aggressive plant, great if need to cover fences, wonderful flowers but you have to be aggressive back to restrain this plant.
Comment: Are there different kinds? I have a lot and I pull it up frequently with no problem. The deer love it also ( East TX).
Comment: No reaction of any kind. And as a child at my aunts in southern WI , I would put the flowers on all my fingers. The side of her house was totally covered with it. The beginning of my interest in horticulture ?
Comment: no flowers on it. i pulled a lot of it up thinking it was a bindweed and because it was pulling down the fence between my mom-in-law's yard and the neighbor's. i'll investigate further now i know what i'm dealing with. thank you, stormy.
Comment: So you pull it up and no irritation or rash?
Comment: @blacksmith37  Something is up with you and plants.  Grins!  I've no reactions either to Trumpet Creeper but had to hesitate whenever adding them to a landscape.  Individuals are different with sensitivities.  I've always had horrible hay fever but didn't keep me from haying most of my teenage life!  I wasn't very pretty or fun to be around as I growled moistly with swollen eyes and dripping nose, grins!  So this Campsis radicans was partly responsible for you becoming a plant person?...very cool. Hopefully you have one of these gorgeous plants to remind you of your ROOTS!
Comment: I did have a bad reaction to poison oak. Took an herbicde and wiped it out near my house.


I believe my ex is using DHS to create problems for me, what can i do?

Question: I have recently received a visit from child protective services. The visit was due to a report of possible neglect regarding my youngest child. I am confident after speaking with the social worker that this will be closed and deemed non-founded within a weeks time. I understand that reports are made anonymously and the identity of the reporter cannot, under any circumstance, be released. I however do not need it to be. I know it was my ex who reported. we are currently in a custody battle, and things have not gone in his favor thus far. However there has been a huge problem, the sheriff accompanied the social worker. that fine, i understand the need to do so. However we live on company property. The day after the visit my husbands employer told him this type of thing could not happen again. It looks bad on the company and if it happens again my husband will loose his job and our home as well. i am confidant that i have nothing to fear from the matter of DHS or anything of the sort. But I am also positive that my ex has discovered he can make my life troubled, by making reports (even non founded ones) to DHS. is there anything i can do to prevent my ex from costing us our home and my husbands job by making false reports, thus sending more police to our home for no reason at all?
Comment: It seems that you live in the US and that DHS is a state agency (not the federal Department of Homeland Security).  Is that correct?  More importantly, what state do you live in?
Comment: Define DHS and use proper capitalization would help.
Comment: The state in question does matter.
Comment: What you can do? Hire a Lawyer. Not ask random people on the Internet.
Answer:
is there anything i can do to prevent my ex from costing us our home
  and my husbands job by making false reports, thus sending more police
  to our home for no reason at all??

Many laws are similar across states. Thus, in your jurisdiction there might be a statute akin to Michigan's MCL 722.633(5), sanctioning "[a] person who intentionally makes a false report of child abuse or neglect under this act knowing that the report is false".
Since the sheriff got involved, there must be a police report reflecting that. You might want to approach the general attorney or police so as to proceed in accordance with the remedies provided by statutory law.

The day after the visit my husbands employer told him this type of
  thing could not happen again. It looks bad on the company and if it
  happens again my husband will loose his job and our home as well.

Although the incident from the false report evidently harmed your husband's reputation with respect to his employer, suing the false accuser at this point in time unfortunately seems a long shot. That is because the court would conclude that you have not suffered special damages. Likewise, applying the current case law, a finding of defamation per se would be hard to establish under the circumstances.
(Note: I am not knowledgeable of child custody laws, so I am not aware of whether the false report bears any relevance in family court)
However, if you or your husband suffer any losses as a result of unjustified actions directly or indirectly caused by the false accuser, he (the false accuser) would be liable for defamation and/or tortious interference with employment relation. The concept of losses not only includes termination of employment, but also other detrimental effects such as demotions and any new costs derived from having to move out of company property.
If the false accuser is aware of the link between your home and your husband's employment, a claim of tortious interference will be more evident because that awareness is one of the prima facie elements of that claim. (For more info on the prima facie elements of a claim, see leagle.com)
Immunity does not protect a person who makes reports that are knowingly and intentionally false. By law, the court can always order the agency to disclose the identity of the person(s) who made false reports that the agency determined were unfounded. See Michigan's MCL 722.625.
Answer: Talk to the attorney you have for your custody situation. If you don't have an attorney, find one. Google for free or low cost legal aid in your city or state. If you don't qualify due to income, they can make referrals.
You need an attorney to deal with the X (and their attorney), to carefully appraise your husband's company about the situation, and to interface with DHS and the state legal department, if needed.
The idea is not to threaten your X with legal action, or your husband's company if he is fired, or to push back against DHS; the idea is to be sure you (and your husband) don't do any of those things yourself, while making sure all parties know you are prepared to defend your position with legal representation, if needed.
I'm not going to try and predict or advise what might happen if DHS visits again, or your husband is fired, or your custody fight gets worse; that could be legal advice, which is off-topic here (and illegal). You need to deal with your own attorney.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/81732/discussion-on-answer-by-bluedogranch-i-believe-my-ex-is-using-dhs-to-create-prob).


Non-losing strategy for white

Question: If you modify chess so that white gets to make one extra move within the first 10 moves, is it possible to show there is a non-losing strategy for white?
Answer: Student T gives an explicit answer, but you can also view it from a game-theoretical perspective.
Suppose normal chess is a draw (or a win for black). Then, white can play 1. Ng1-f3 and Nf3-g1, effectively becoming black and the rest of the game is normal, so it is a draw (or a win for white).
Suppose normal chess is a win for white. This will almost certainly involve moving a pawn two steps from its initial position within the first 10 moves, or moving a bishop, queen, rook or king. You can use your extra move to perform this move in two steps, e.g. e2-e3-e4 or Bf1-d3-e2.
In any case, White will not lose the game.
Comment: This is a non-constructive proof. You must be a mathematician!
Comment: @jknappen - the second tempo is 'paid' by the extra move White gets. And DagOskarMadsen, you are right.
Comment: That is a very elegant answer!
Comment: This is not a proof. The knight manoeuvre cost two tempi, not only one. Thus it does not prove that Black has no winning strategy.
Answer: Yes. 1.e4, then move the white Queen out to f3|g4|h5. Prepare for Qxf7+ then Qxe8 or Qxd7+ then Qxe8. Now white wins because the black king is gone.
Comment: Say 1.e4 Nf6. Can you win Black's king by force now? Or are you just going to grab a piece? Can you prove that White can win or draw with an extra piece?
Comment: 2. e5 and your knight can't run (otherwise 3. e6 wins) so white can at least grab your knight without using his extra move.
Comment: 2.Bc4 can give Black some trouble.  1.e4 Nf6 2.Bc4 (threatens 3.Qh5,Qxf7#) g6 3.e5 (threatens 4.e6,exf7# or 4.Qf3,Qxf7# if the knight moves anywhere but d5, where it is lost.) e6 4.exf6. Now if 4…Qxf6 5.Qf3,Qxf6 and if anything else then 5.Qg4 threatens 6.Qxe6,Qxf7# or even just 6.Qxe6,Qxe8#. 5…Be7 doesn't prevent mate on f7, and 5…Qe7 or 5…Qf6 loses the queen. Also 5…d5 just loses to 6.Bb5,Bxe8#  Sacrificing the knight on d5 on move 2 or 3, followed by e6, seems best for Black, but probably still loses.

Non-losing strategy for white


Thymolphthalein solubility

Question: I already know that thymolphthalein is soluble in alcohols, very alkaline aqueous solutions, acetone, and propylene glycol methyl ether.  My questions are what other solvents dissolve thymolphthalein, and what additives increase solubility (for example, specific surfactants)?
Answer:
One expects [poly(ethylene oxide)-co-(polypropylene oxide)-co-poly(ethylene oxide)] triblock surfactants will micellize it (e.g., Pluronics); possibly Tergitols.  It looks too bulky to fit inside even gamma-cyclodextrin.
Hang a suitable side chain off the phthalic anyhydride and the product will dissolve in pretty much anything.  What does pH mean outside water?

Thymolphthalein solubility


metadata of All THE FIELDS OF ALL THE OBJECTS

Question: We are trying to make a list of all the fields which we have created between our two consecutive releases.
We need the metadata of All THE FIELDS OF ALL THE OBJECTS for this reason, so that we can identify the fields created recently using the created date. We have about 407 objects.
Please suggest any way that it can be done or if there are any applications which would assist in this.
Answer: You can try Schema Lister.
Check the below link
https://schemalister.herokuapp.com/

Select your environment and API version
Authorize the Apps through OAuth and it will generate a list of all
the objects and fields.

The benefit of using this app is that you don't need to install anything in your Salesforce org and don't need to provide your Salesforce username and password.
Let me know if it helps.
Comment: Thank you for the quick response. I tried it, however, it gives a list of objects, its fields, labels and api names and field type. It does not have other attributes like created date or modified date. We need these attributes to filter the fields based on when they were created. Please suggest.
Answer: The Metadata API will NOT return all the Object Names and Field Names. Instead, it provides a specific "view" of Custom Objects and Fields that are relevant to Metadata connections. Salesforce calls these "channels." You need to use the SOAP Describe API to globally list all of the objects, and then Describe all of the fields. This will provide what you are asking for.


LDAP mounting home over network

Question: Guys i am working with LDAP and was successful in making the user logging in using PAM but how can i sync the directories so that if the user logs in and saves any data in his home folder can access all his data by logging in anywhere in the network.
Ultimately i want that the LDAP user can access his home data anywhere in the network.
Answer: Your server containing the home directories can share them via NFS and the clients can mount them.

LDAP mounting home over network


Where are all the native revisioned databases?

Question: I've read all the SO questions, the Coding Horror articles, and Googled my brains off searching for the best ways to revision control data. They all work and they all have their appropriate implementations based on use cases and so on. What I really want to know is why hasn't a database been written to natively support revisioning on the data-level?
What I am baffled with is that the API is already practically in place with transactions. We start a transaction, change some data, and commit. We are authenticating against the database too so blame is present. My company stores end of month versions of our entire database for accounting purposes which equate to tags. Does this not scream RCS?
Branching is something that databases could benefit from greatly too in regards to schema more than data. Since I really only care about data and this would increase the difficulty of implementation by a massive degree I'll stick to just tags and commits.
Now I know that databases are incredibly time-critical applications so any unnecessary overhead is shunned into oblivion and some databases are epic-level huge and revisions will only exponentiate that size. A per-table, opt-in revision control undoubtedly has a place in small to medium scale environments where there are milliseconds to spare and data history has a degree of importance. I want commits, I want logs, I want reverts, I want diffs, I want blame, I want tags, and I want checkouts. I want MF-ing revision control.
I have a question in there somewhere...
Answer: You could read about temporal databases.
In "Temporal Data & the Relational Model" by Date, Darwen, and Lorentzos, the authors introduce a sixth normal form to account for issues in tracking temporal data.
Richard Snodgrass proposed TSQL2 as an extension to SQL to handle temporal data.
Implementations include:

Oracle Workspace Manager
TimeDB
Comment: I'm surprised I have never heard of this but it looks very promising as to what I have envisioned in my head from a quick read of the Wikipedia article. I'm not looking for anything production ready, just something to hack around with.
Comment: Wow - so TSQL2 was a child of the 90's. Pre-wikipedia days.

I think it needs to be awoken cos the soil for those seeds of ideas is a bit more fertile these days.
Answer: One native solution is Oracle's Flashback Database (aka Total Recall).  It is a chargeable extra to the Enterprise Edition, but it is pretty cool.  It transparently stores versions of the data for as long as we want to retain it, and supplies syntax to query old versions of the data.  It can be enabled on a table-by-table basis.
Essentially Flashback DB is like using triggers to store records in tracking tables, but slick, performant and invisible to normal working.
Answer: Several DBMSs implement engine-level versioning mechanisms. Unfortunately there is no vendor-independent standard for this so they are all proprietary. Oracle flashback has already been mentioned. Microsoft's Change Data Capture feature in SQL Server is another one.
Comment: *"Several DBMSs implement engine-level versioning mechanisms. Unfortunately there is no vendor-independent standard for this so they are all proprietary"* I know this answer is written before 2011, but the ANSI/ISO SQL 2011 standard has added this to the standard.. The syntax is more os less `WITH SYSTEM VERSIONING` to the `CREATE TABLE` statement and a range with `TIMESTAMP(6) GENERATED ALWAYS AS ROW START|ROW END` for the columns..
Answer: You forgot I want performance. A DBMS is a pretty low level data storage mechanism, and in systems with billions of rows, performance can be important. Therefore, if you want this sort of auditing system, you can build it yourself using the tools available to you (eg. triggers).
Just as in a filesystem, not all files are appropriate for version control, in a database not all rows would be appropriate for version control either.
Comment: I have done the trigger route which is okay and fully in-application logic and they both definitely work but I just don't know why none of these exist. I would like to see a revision comprise of changes to more than one row and even more than one table, however. And as I said this would have to be an opt-in and per-table addition as performance is always important. I guess since this couldn't be done on a large deployment effectively is why it has never been implemented in mainstream DBs. Boy would a few of my smaller, more specialized web sites and applications benefit, though.


How to remove a broken tub drain

Question: By the looks of things, a "handy" homeowner glued a tub drain in place well over 20 years ago. The metal is now so corroded and brittle that it's falling apart with minimal amount of pressure. It has no crossbars for a drain key, it's too brittle for an extractor, and there's barely any metal left for pliers (just a bit where the threads were glued). I'm at a complete loss as for how to remove this thing.
Comment: A thin small screwdriver   Work it slowly between metal and plastic threaded area until you can get needle nosed pliers in. Then peel the metal away from the plastic
Answer: Get a hacksaw blade and slowly cut a vertical slot in the metal. Check the cut often because you don't want to cut into the threads, just touch them. Then try to bend outward at the cut. If it doesn't break at that point, cut another slot the same way about an inch away from the first slot and pry that section out.
Comment: Thanks mate! My hacksaw has terrible teeth and it wasn't doing much more than surface scratches. It gave me an idea tho, and I was able to get it off in a few seconds with a dremel. Threads are still in tact and a new drain has been installed.
Comment: Glad it worked out....  Good question and good photo for your first one.
Answer: I've successfully used what I call an inside-out pipe wrench.  It grabs the inside of a pipe.
The correct name is a Drain Key.   It was a little awkward to use but it works.  There are other models and versions.

https://www.grainger.com/product/SUPERIOR-TOOL-Drain-Key-Drain-Key-1TKC2

How to remove a broken tub drain


is this the right way to ground fault protect both sides of an mwbc?

Question: is this the correct way to ground fault-protect both sides of an mwbc?
 pigtail the (line) neutral to two separate gfci outlets, and pigtail the (load) neutrals to the neutral that's going outside.
Answer: Close, but not quite.  From the point of the two GFCIs onward, the neutrals must be kept separate.
Consider: if you had a device drawing power on the black hot circuit from a load farther down the line, and nothing on the red, which GFCI would its neutral return current flow through?  Since they're just connected in parallel in your diagram, it would flow through both, and then trip both, since current out is not equal to current in within each GFCI.  If you separate the neutrals, you can make sure all the current from the black hot flows back through its proper GFCI, and none crosses over to the other one.
Also note that this scheme will fail if you use any 240V devices on this circuit.  The only way to do a mixed 120/240V circuit is with a 2-pole GFCI breaker.
Answer: That drawing cannot possibly work. Right off the bat, you are paralleling, providing two paths for neutral to go. That itself is a code violation, nevermind the GFCIs.   It won't work because as Nate Strickland describes, neutral won't know which path to take.
GFCIs involve looping all the wires of a circuit through a current transformer, where each wire creates a magnetic field and all the magnetic fields should cancel each other out.  Therefore, all the wires of the circuit have to go through ONE current transformer. Any scheme where a GFCI doesn't handle all the wires, can't work by definition.
I gather you have an existing MWBC that stops at several junction boxes, and you need to GFCI protect them all.
Solution: A 2-pole GFCI
So only a 2-pole GFCI will work.  I've never found one offered as a stand-alone GFCI (deadfront).  Mainly they seem to appear as 2-pole GFCI+circuit breaker combo's.  And those always take 2 full spaces.  And they must be listed or classified for your panel, so unless you have a modern GE, Eaton, Sq.D. or Siemens panel (or Challenger which take BR), you could be in trouble. Check Eaton's CL line which fits some panels, but you could be out of luck.  In that case, it's "subpanel time".
Solution: Don't use Load terminals
You're not required to use Load terminals.  You certainly can install GFCI receptacles and leave the warning tape on the "Load" terminals. Just then, the downline "rest of the circuit" won't be protected.  Place all the wires on "Line" (most GFCIs permit 2 wires per screw, but remember, you already need to pigtail neutral because it's a multi-wire branch circuit!)
This means downline receptacles will not be protected, and you will need separate GFCI receptacles there as well if you need protection there.
Comment: Are you saying that keeping neutrals separate after the GFCI won't work?  Or are you assuming that isn't plausible on already-installed wire because there isn't a second neutral?
Comment: @JPhi1618 I'm saying his drawing won't work.  Which means yes, if there's a pre-installed situation of 3-wire connecting to a junction box of outlets, then onward as 3-wire to another junction box of outlets, then he is sunk indeed.


How do I replace the Magento favicon?

Question: I'm trying to replace the Magento favicon, but I can't seem to find it. Where is it?
Answer:
First point, check the source of your front page

if you found a meta like this: <link rel="shortcut icon" href="a/path/favicon.ico" type="image/x-icon" /> just change the favicon in the named path

Else, browsers try to get the favicon to the root of your website so:

either you put a file favicon.ico at this place
or you put a meta like above with the good path to your favicon.
Comment: This only works if you have just one shop. Better upload the favicon to the theme.
Answer: The easiest way is to add the favicon meta tag to your theme's header and point it to the favicon in your root. A more complex way (I think) is replacing the favicon in /skin/frontend/theme/interface/favicon.ico, but I never had any success with that method.
Comment: The path is basically `$MAGENTO/skin/frontend/package/theme/favicon.ico` thanks it fixed it :)
Answer: You can also consider using rewrite and completely bypass Magento:
.htaccess:
RewriteEngine on
RewriteRule ^favicon\.ico$ /images/favicon.ico [L]

Comment: It works, but it's not preferred I think. Better do it right in the template, less confusing. And if you have multiple shops with multiple designs and multiple favicons, you need to use conditions in the htaccess. All in all you better upload the favicon to the template.

How do I replace the Magento favicon?


Add color to part of a mesh or OBJ Qt3D 5.9 in QML

Question: In Qt3D 5.9, I am using scene 3D to render an .obj file and display it. I also have enabled object picking, so when a user selects part of the object, I know exactly where on the model they clicked. What I would like to do is add color to that part of the obj/mesh that the user clicked on. To be more specific, for the 'y' value that the user clicked on, I want to color a line all the way around the object model on that 'y' value. I've looked around online and can't find anything to help. Unfortunately I'm not familiar when it comes to 3D objects, meshes, etc. How can I color just part of a mesh in Qt 3D 5.9?
Answer: Since you managed to load your own meshes, I suppose you understood how the GeometryRenderer and Geometry QML Components work. The Geometry component takes attribute that define (for instance) the position and normals of your object. The names you give to these attributes allow you to retrieve them in custom shaders. You can add an Attribute in your geometry that defines a buffer in which you will store vertices colors instead of positions and normals.
Then, you will need a custom Material (If you haven't a custom Material, try to read the QML doc to understand how it works. I know, the doc is not really complete but it is a good start)
This custom material will allow you to call your own shader, in which you can retrieve the color of a vertex in the same way you retrieve it's position.
So to conclude, since you want to color just a part of the vertices, you will need

A buffer containing all the colors of all vertices of your mesh
A Geometry attribute that tells how to read this buffer
A script that update the buffer on selection
A custom material and a custom shader that uses the color buffer to paint the object

This is a not-so-easy thing to accomplish, but it is possible and should give you a better undestanding of how Geometry, Materials and shaders work in QML.
If you are not familiar with these, I would suggest that you first put asside the par vertex color buffer and try to make a custom shader that paint all your object red. From that you will be able to go on and find out how to pass per vertex colors to your shader
Good luck


Making a residual plot in multiple linear regression

Question: I need to make a residual plot and I was wondering whether I make the plots in multiple linear regression on one independent variable at a time (like making a simple linear regression) or the all of the ten independent variables at the same time (like multiple linear regression)? They produce different results for me obviously.
Comment: Hello - "residual plot" can refer to many different things.  What is your goal?  Also you may want to look into partial plots, a.k.a. partial regression plots.
Comment: My goal is to check heteroscadisticity and linearity of the data. I have ten independent variables and I'm not sure whether to plot the residuals individually against dependent variable or all of them at the same time, like when doing a multiple linear regression
Comment: Each plot is valuable, and in addition you should inspect fitted values versus residuals. But no finite amount of plots will be guaranteed to "catch" heteroscedasticity or non-linearity if it exists.
Answer: To check for overall heteroscedasticity:

On the Y-axis:  your model's residuals
On the X-axis:  either your dependent variable or your predicted value for it.  You might try a plot using each.

Note that John Fox in Regression Diagnostics finds that, typically, only when the variance of the residuals varies by a factor of three or more is it a serious problem for regression estimation.
To check for overall linearity:

On the Y-axis:  your dependent variable
On the X-axis:  your predicted value for the dependent variable

Then you might create a linear fitline and one using a lowess and/or a quadratic or even a cubic fit, to compare to the linear one.
To check for heteroscedasticity, linearity, and influential points with respect to each X-Y relationship:

Create partial plots, a.k.a. partial regression plots.  Each will
show an individual X-Y relationship while controlling for the other
predictors.


Multidimensional Array Object allocation

Question: So far, I'm trying to create a 2-Dimensional JSON array to hold a series of shapes inside a series of 'frames'. So far I thought I had it, but I can only push shapes to frame[0]; as soon as I pass it frame[1] I get the error Uncaught TypeError: Cannot read property 'shape' of undefined.
Why can't my browser recognise frame[1] as a potential next storage area for the frame array? Is it something to do with how I've initialised the JSON Array?
Relevant code so far:
function Obj(type, x, y, w, h, r) {
"use strict";
this.type = type || null; //rect, crcl, line, text
this.x = x || null;
this.y = y || null;
this.w = w || null; //used for rect, line
this.h = h || null; //used for rect, line
this.r = r || null; //used only for crcl
}
var keyframes = {
    'frame': [{
        'shape': []
    }]
};

var shape1 = new Obj('rect', 20, 20, 20, 20, 0);
var shape2 = new Obj('crcl', 20, 20, 0, 0, 20);

keyframes.frame[0].shape.push(shape1);
keyframes.frame[1].shape.push(shape2);

Answer: It does recognize frame[1] as a potential place to put something, but you haven't put anything there.  Your code expects frame[1] to be a reference to an object but you only initialize the first element that way.
keyframes.frame[1] = { shape: [] };

will initialize the next element. Without that initialization, keyframes.frame[1] is undefined.
Comment: Perfect, now I just need to remember to initialise the next frame each time one is created. Thanks!
Answer: PROBLEM:
Your initialization of keyframes is as follows:

an object
contains a 1 element array 'frame'
'frame' contains an object

You CANNOT access keyframes.frame[1] because it does not exist (frame is a 1 element array so ONLY keyframes.frame[0] is valid)
SOLUTION:

Create the keyframes.frame[1] element

keyframes.frame.push({shape: []});       //now keyframes.frame[1] exists

push shape 2 to the object added above as you attempted before

keyframes.frame[1].shape.push(shape2);       //this should now be valid


Android GPS Tracker is not disabled

Question: Here I am facing an issue with GPS in android.
In my code I am just displaying a marker on the map based on the current location, and its working fine.
When i call this code GPS Tracker Engine Symbol is coming at the top of the screen.
And in the onPause() method I am calling myLocManager.removeUpdates(this) ,but even I am out of that activity *that GPS Tracker is not disabled..
Which become a big headache for me because it consuming more battery even app is in Sleep mode.
I am using  MyItemizedOverlay to draw the marker when location updated.
Can any one please help me how to solve this..?
Thanks in advance.
Answer: Are you using MyLocationOverlay to display your current location?
MyLocationOverlay handles location updates on its own, i.e. it uses GPS. Call .disableMyLocation() to stop location updates.
Comment: Thanks for the Reply.No I am using MyItemizedOverlay.How can I disable my location in this case.

Android GPS Tracker is not disabled


SQL Server database optimization for large database

Question: I am developing a website with huge data which to be stored in SQL Server database. How should I optimize it to make it faster.
1. Using Stored procedures.
2. Functions / Views.
3. Any other methods
Comment: how huge is huge for you in Gb ?
Answer: Well, the most important thing would be to use appropriate indexes on your table that have large amounts of data stored in them.
You also might consider using partitioned tables.
Usind SPs or Views won't make your database faster.
Answer: The most important thing to know in database tuning is how the data will be used.
Indexes can do wonders for increasing data retrieval speed. But over-indexing can create huge performance bottlenecks when writing data. (The indexes need to be updated as the data is written. This can, in the worst case, make your writes take several times as long as they would without the indexes.)
Likewise with views. A good indexed view can be a wonderful thing for performance and manageability if the data is largely read-only. But they can really drag a database down on writing.
Partitioning can be critical. If your data lives on a quality storage medium with lots of spindles, you can partition your data so that the most referenced data is spread across different spindles. That way you don't have read heads sitting idle while several requests are queued up on one drive.
Depending on your data access needs, it is also a popular ploy to setup multiple databases, only one of which can be written to. The others are all read-only copies. That way, you can query and analyze the data in an almost real-time fashion (if that is acceptable) and spread the load out across servers.
Finally, query tuning is very important. You can use the tools that come with SQL Server to help tune your query. Often, you don't even need an index to drastically improve read performance. You just need to alter your query to avoid unnecessary columns (that may rule out an existing index, for example) or unnecessary joins, sub-queries, etc.
Answer: Of course other methods
1) Optimization tables structure(if posible)
2) Optimal indexes structure(complicated indexes, included fields)
3) Partitioning(if server's a few physical disks)
4) SQL data compression (only Enterprise edition)


SYN scan victim sending back RST

Question: I'm confused on the case of SYN scan and closed ports (the case of open ports makes sense). So, the attacker sends a ~40 byte SYN packet, a "closed port" would send a RST packet back to the attacker and is thus "unexploitable". Does this mean that the attacker can't send another SYN packet to the closed port to continue attempting to flood it? Or does that just mean that this port is unexploitable by other means but another SYN packet can be sent and the attacker can continue the process forever?
Answer: It depends on what the attacker is trying to accomplish.
Usually the goal with a network scan, is to identify active hosts on a network, and what services they offer. Either for the purpose of attacking them or for network security assessment.
You're describing a SYN flood attack, which is different than a scan.
A SYN flood occurs when a host sends a flood of TCP/SYN packets, often with a forged sender address. Each of these packets is handled like a connection request, causing the server to spawn a half-open connection, by sending back a TCP/SYN-ACK packet (Acknowledge), and waiting for a packet in response from the sender address (response to the ACK Packet). However, because the sender address is forged, the response never comes. These half-open connections saturate the number of available connections the server is able to make, keeping it from responding to legitimate requests until after the attack ends.
In the case the port is actually closed, you won't get any half-open connections, but you could possibly saturate the targets connection with packets, which would be a denial of service attack as well.
Answer:
Basically you are mixing up two different phases of hacking methodology. Purpose of a syn scan is not to attack but to gather information (pre-atttack phase) and flooding would be carrying out a real attack once you have found out a vulnerability.
The purpose of port scanning is to find out the open ports and applications listening on those ports. Basically discovering exploitable communication channels.
If the port is closed there is no communication channel. The port will not accept any kind of packets.

Flooding attack is an attack that attempts to cause a failure in a computer system or other data processing entity by providing more input than the entity can process properly

If you keep sending syn packets to a closed port (like you mentioned) it can not be considered as flooding as your packets are not being accepted by an application. You may be flooding the bandwidth by generating a large number of syn packets.
Answer: In a "SYN flood" attack, the attacker wants to make the target server allocate resources to handle apparent connection attempts. The attacker sends SYN packets which tell to the server "I want to connect to port n". If there is, on the server, some software which currently expects incoming connections on port n, then the server responds with a ACK+SYN packet and, more importantly, reserves some RAM on the server to maintain the state associated with the alleged new client. However, if there is no software listening on port n, the server respond with a RST (which some firewall may or may not drop, by the way), and reserves no RAM.
It is not the sending of the RST which makes the attack fail; what makes it fail is that the server reserves no RAM in that case. The server will not drown under the half-open connections since it forgets them immediately.
If the attacker receives a RST packet, then he knows that his flooding attempt is ineffective, but that's just a byproduct. Note that the main advantage of the SYN flood attack (advantage for the attacker) is that the attacker needs not receive any response from the server, so he may use fake source addresses (that's called IP spoofing), which helps him covering his tracks. If the source address is spoofed, the attacker, by construction, never sees any response packet from the server, be it ACK+SYN or RST.
Comment: If the server doesn't respond to the SYN, then this means that the server is not expecting connections on that port, i.e. is immune to SYN flooding on that port.
Comment: If the server doesn't respond to the SYN, does that mean it's more difficult for the attacker to DoS the server?
Answer: Yes, you can continue to send SYN packets to a closed port all you want, but at that point you'll just be exhausting bandwidth.
Exhausting system resources is done with systems that actually respond and allocate resources such as memory to expected subsequent interactions, so that type of attack isn't possible with closed ports.
Just keep in mind there are numerous types of DoS: some bandwidth, some system resources, etc.

SYN scan victim sending back RST


Is prime order group used in ECDSA unique?

Question: In ECDSA, we use a prime order group $\langle G\rangle$ for cryptographical use. Assume $\#\langle G\rangle = p$. Is there another subgroup in the curve used for ECDSA whose order is also $p$?
Answer: This question has two faces;

The number of rational points of the used curve is prime like secp256r1, i.e. $\#C(K) = p$ where $K$ is the field where curve $C$ is defined;
In the group theory, let $G$ be a finite group and $H$ be a subgroup of $G$.
Then the order of $H$ must divide the order of $G$. This the Lagrange's Theorem in group theory. More formally;

Lagrange's theorem - If $H$ is a subgroup of a group $G$, then ${\displaystyle \left|G\right|=\left[G:H\right]\cdot \left|H\right|.}$

Below a corollary to the Lagrange theorem;

If the order of the group is prime then there are no subgroups other than the trivial subgroups.

Therefore, an order $p$ group has no subgroups other than the trivial subgroups which are the identity group and the group itself.

The number of the rational points of the used curve is not a prime,  $\#C(K) = n$;
This really depends on the group. The Lagrange theorem doesn't guarantee the existence of the subgroups if an integer divides the order of the group.
Consider the Curve25519 which has a prime order subgroup $n$ and the co-factor is $h=8$ ( $h = \#E(\mathbb{F}_p)/n$) then we have the subgroup of order $2,4,8,n,2n,4n,8n$, i.e. we have all possible subgroups.
You can find a group that has two prime subgroups of order $p$ the if there are no other subgroups the curve group will be isomorphic to $\mathbb{Z}_p \oplus \mathbb{Z}_p$. Is this possible in Elliptic Curves?
I haven't seen an example in secure elliptic curves. The reason is simple; we want a large prime subgroup order that is close to the curve order in order to effectively use the curve. If there are two different subgroups of order $p$ then the curve order will be $\geq p^2$. This means you are wasting your computations.

More into theory (4.1 is in the second edition of Washington's Book);

Theorem 4.1: Let $E$ ben elliptic curve group over the finite field $\mathbb{F_q}$. Then $$E(\mathbb{F_q}) \simeq \mathbb{Z_n}
> \text{ or } \mathbb{Z_{n_1}} \oplus \mathbb{Z_{n_2}}$$ for some
integer $n \geq 1$, or for some integers $n_1,n_2 \geq 1$ with
$n_1|n_2$.

If the $E(\mathbb{F_q})$ falls into the first case implies that the subgroup order $r$ must divide $r|n$. But the subgroups of $\mathbb{Z})_n$ are unique. Therefore there cannot be two subgroups that have the same order.
The second case is more interesting [1] [2] [3] since it is a direct product of groups. Since $n_1\mid n_2$ there is a subgroup of $H$ of  $\mathbb{Z_{n_2}}$ such that it is isomorphic to $\mathbb{Z_{n_1}}$. Now we have two subgroups of the same order $\Bbb Z_{n_1} \oplus \{0 \}$ and $\{0\} \oplus H$.
As said before we don't prefer curves that can have two different subgroups of order large prime.
Comment: Yes, I guess there is no another such subgroup in the ECDSA-used curves due to the efficiency concern. But I am just not sure. This is important for my work. Thanks for your answer!
Comment: @user77340 if you are not using a self-created curve, then no! You may see the details of the curve on their paper.


LtSpice antisymmetric sine pulse

Question: I am trying to create a pulse voltage source in ltspice. The pulse should look like a half cycle of a sine wave however the rise and fall times should be different. I can create such pulse with the PULSE function of ltspice and can create a half cycle sine wave but I don't know how to create a nonsymmetric sine pulse. The rise time should be 10 microseconds and fall time should be 15 microseconds. I added a picture that I drew for you to visualize.
Thanks in advance.
Comment: Does LTspice have "switch" component?
Comment: Not like a real one that you can open and close but it does have switches that are controlled by voltage or current.
Answer: This is not a very beautiful approach, but it works (for this signal).
First I created two voltage sources, which provide the two halves of the signal.
So V1 is SINE(0 8 25k 0 0 0 0.25), a 25 kHz sine but only for a quarter cycle, so that it stops at the maximum value.
V2 is SINE(0 8 16k6667 10u 0 90 0.25), 16.67 kHz sine but shifted by 90° so it starts at the maximum, again for a quarter cycle, so that it will stop at zero.
The real output is then a BV-source with V=min(V(Vout1),V(Vout2)) so it outputs always the smaller of the two voltages, which works in this case because one starts at the maximum value and the other one stops at the maximum value.
The frequencies are easy to calculate: it's just \$f = \frac{1}{4 \times t}\$ where t is either the rise or the fall time.
Comment: Thank you so much for your time. I had tried the same thing with using 2 voltage sources but the one I inverted with 90 degrees always had a DC voltage at the beginning so I tried to subtract that DC with another voltage source and it was not efficient as this one and also have other problems. Turned out I was completely wrong with the frequency calculations. I found the frequency of each voltage source as they are normal sinusoids and then specify the cycle number as 0.25. I still don't understand what is wrong in my approach but yours worked out perfectly. Again thank you.
Comment: @Arsenal You could reduce your approach by only using two sources: voltage `sin 0 8 {50/3} 10u 0 90 0.25 rser=1`, and current source (pointing down) `sin 8 8 25k 0 0 0 0.25` in parallel. You reduce the behavioural source, while having a convergence-friendly solution, and with only one node, which will also behave like a quasi-real source by having an output impedance. If you need repetition, you could make use of the builtin `MODULATE(2)` with an FM-pin driving source.
Comment: @EkinAlparslan hmm, your approach doesn't sound wrong. Without the netlist it's hard to tell. Probably a minor mistake which takes hours to figure out :D Glad I could help.
Comment: @aconcernedcitizen that is an interesting approach and I think worthy of an own answer. Like I said, this was just the first thing which came to my mind and those ideas typically aren't very beautiful.
Comment: @Arsenal Nothing interesting about it, feel free to modify your answer with it. :-)

LtSpice antisymmetric sine pulse


Will Totem be substituted by Banshee?

Question: since Banshee now can play videos with subtitles, probably in few months it will gain full dvd menu support, and is in strong development, will it be the time to remove Totem form the default application list? I guess so.
Thanks.
Answer: I believe it is too early to say whether Totem will be replace with Banshee in the future. While it is a good idea, Banshee does not yet have full support for Video Library management, so it is not really meant for being your dedicated video player.
Totem is more mature, and while it does not have library support, the fact that it is a dedicated video player means it is more likely to hang around for quite a while until Banshee is more mature in that aspect, and able to replace it completely.
Comment: I agree that it is too early to tell.  IIRC, there's been talk about writing a minimal, 'library-less' interface for Banshee, which could make it a better replacement for Totem, in my opinion.
Comment: @MichaelMS: That might make a lot of sense :) - my only problem would be that Banshee is evolving well into a Windows Media Player replacement, and in many ways that will attract converts from windows.
Answer: Unfortunately, I believe in this possibility in the not too far, the Banshee to time is becoming a player full multimedia, although heavy consumption features of the PC. And now as the default Ubuntu tends to be more developed, these resources are still assumes no it. But in terms of video, vlc is very complete.
Answer: Totem supports playing audio on the fly i.e. when you place your mouse pointer over a music file, it plays it straight away. If banshee can support that I think they might consider.
Comment: That's the file manager (Nautilus) that does that. For proof, open the file manager and go to Edit>Preferences>Preview.

Will Totem be substituted by Banshee?


How to get started with fingerprint recognition?

Question: I have started with Matlab and Digital Image Processing. I am trying to do Fingerprint recognition. I found many research papers regarding this but I am unsure where to start. Concisely, what is the most basic approach/algorithm for doing fingerprint recognition ?
Comment: Have you learnt the basics of image processing yet? Perhaps getting upto speed with that and then attempting something more challenging like fingerprint recognition might be a better idea. On the surface, it is as simple as pattern matching with a stored template, but when you dig deeper, there's different layers of advanced topics involved like identifying fingerprint patterns like ridges and whorls, knowing what features to look for and store (you can't do pixel matching on a database that could be in the millions) aligning and orienting the sample correctly with the template, etc.
Comment: Ideally you should always have done your research before posing a question here.
Answer: This  may help you.
Also, everything related to fingerprinting in here.
I think is a good documentation to start with and view some source code. Nevertheless, you should learn some other algorithms before you start coding.
Answer: The following are the basics of image processing for finger prints

Make sure you understand what a finger print is. It is basically a signature for every human being. Every finger on each hand on every person (even twins) have unique patterns. These patterns are of interest to you.
These patterns are classified into categories. Deltas, circles etc.
You must understand what valleys,ridges, bifurcations, etc are.
Once you understand the two above and a bit more, you go onto fingerprint acquisition.
Once you have an image. The interesting and difficult part begins. Such as segmentation, enhancement of certain patterns, noise reduction, finally encoding.
The encoding part is the penultimate part. When you have an filter/processed image, you create a digital signature which is called encoding. This signature is what the whole fingerprint ended up in.
You then create more digital signatures for other images.
You make comparisons of these images, trying to figure out matches.
Matching itself is another story. Where you will try to see false matches and true matches.

Still there are plenty of other things you need to do. But these are the basics. Lengthy but you can do it if you have interest in it  :)
List item
Comment: Well there are so many techniques out there. You are on the right track. But Matching can always be different. You could even use Manhattan distances as well. Matching minutias would be helpful. Take a this very good link on fingerprints. Will help you alot http://fingerchip.pagesperso-orange.fr/biometrics/types/fingerprint_algo.htm
Comment: thanks. How do you create a digital signature for these ? I currently store information regarding ridge endings and bifurcations. then I use elastic string matching algo to match them. Is there a better way ?
Answer: Take a look at this repository.
It uses oriented gabor filters to perform noise removal, thereby enhancing the image. It can also recover broken ridges up to a certain extent.
https://github.com/Utkarsh-Deshmukh/Fingerprint-Enhancement-Python


Access static web-server through managed switch

Question: I have three devices:

Windows PC
Managed switch: D-Link DGS-1510-20
Linux Webserver with static IP

Schematic
How do I configure the switch to access the static IP webserver from the Windows PC through the switch in a local Network?
(complete networking noob here..)
Answer: Removed first line - Overlooked link Schematic
A switch is not supposed to access anything but to forward traffic of machines that wants to access a machine within your LAN. In short: a switch is a Layer-2-Relay (See the OSI- or TCP/IP reference model for an explanation of networking layers).
I now assume, that you want to be able to access the webserver on your windows pc which is connected to that switch.
Usually, regardless of whether the switch is managed or not, it should forward traffic to a device without configuration.
To achieve this, your client and your windows-pc must be in the same LAN (say in the same IP-subnet) and either directly or indirectly connected to the switch.
If client and server are not within the same IP-subnet, you may have to configure the switch's routing. Unfortunately, I dont know how to do this on your device.
Also, make sure that the windows firewall is not blocking traffic to your webserver.
-
Note: Switches supporting VLAN's are Layer-3 capable. Otherwise communication between computers across (V)LAN's would be impossible.
To gain a solid knowledge of computer-networking, I recommend Cisco's CCENT Certification Guide. Even if you don't want to get the certificate it provides great explanations of networking fundemantals for people who have never been in touch with computer networking.
Comment: Thank you! I will try to route the client IP to the server IP-subnet (cant be changed).
Answer: if it's layer 2 switch or asuming  you are using layer2 switch then connect your server and pc to layer 2 switch and configure network adapter ip setting
For example
Window pc - ip address 192.168.10.3 Subnet mask :255.255.255.0 Gateway : 192 .168.10.1
Web server :192.168.10.2 Subnet mask :255.255.255.0 Gateway :192.168.10.1
Ensure that both web server and pc is connected to same gateway 192.168.10.1 .. consider this brief example and use your internal ip address you will be able to access server services from pc


Did Valmiki address Rama as the the supreme being when he spoke to him personally in the Uttara Kanda?

Question: Logically he should have because he has already narrated how Brahma and others called Rama as Vishnu and Narayana and the supreme being at the end of the war.
Answer: Valmiki addressed Rama with the words like Dashrathe, Mahavrata Rama etc. But when Sita went into Patala, Lord Brahma addressed Lord Rama as Vishnu:
Uttarakanda, Sarga 98:

I would not have reminded thee of this secret but for the present necessity. Do thou now once more remember thy birth from Vishnu. By nature, Sita is pure, chaste and ever dependent upon thee. And by virtue of her ascetic dependance upon thee she has gone to the region of Nagas. Thou shalt again meet her in heaven (Vaikuntha). Hear, what I communicate unto thee before the assembly.

And Sage Valmiki was present there when Lord Brahma said this as at the end of the conversation with Lord Brahma, Lord Rama said to Sage Valmiki:

O illustrious sir, the Rishis living in Brahmas region have grown desirous of hearing my future history. So let it be taken up next morning.
Comment: Are these shlokas from Uttarakanda?
Comment: yes, they r from Uttarakanda.. @Pandya
Comment: Ok. It would be useful if you mention the location of the verse which sarga of Uttarakanda. I found it is Sarga 98, revised your answer
Comment: @Paṇḍyā Verse numbers are visible from the screenshot itself. Are screenshots visible to you? You could've added them yourselves right? Exact location of verse is upto the OP.
Comment: @Sarvabhouma Sarga number is required to locate the verse


A monkey-like creature with no legs?

Question: Is it possible that a monkey-like creature, in the mountains, could evolve to have no legs and a really strong set of fore-arms? I was thinking that this might be possible because of the climbing skills needed to navigate the environment.
Comment: no there would be no reason that losing the legs in lew of stronger arms would be chosen, in fact medium strength legs and arms will always have better grip than 2 strong arms
Answer: I'm no biologist but I'll give some educated guesses. I'm gonna go with no.
First, if you look at any real monkey/monkey-ish creatures who mostly dwell in trees, not only do all of them have four limbs, most of their feet are "hands" that can grab. Not just that, most of them have tails that can also grab. I'm gonna guess that's because when you're living in trees for your entire life, you're gonna need all the limbs you have to support yourself, in order to move around safely.
That said, speaking of lack of rear limbs, bats have highly devolved rear limbs. If I recall correctly some of them have hooks for feet. Same goes with pterodactyl, because neither need to rely on limbs to travel - they can fly. So, if we're talking about monkey-like creatures with devolved legs, they'll have to be dwelling in highly vertical environment, like high cliffs covered with thick, strong vines all year long. And they'll have to be able to glide around like flying squirrels. And they'll probably need strong tails too.
Answer: The only way I could see something like that happening would be if a species like a cassowary bird were forced into trees from environmental pressures, but would only really have any chance if that niche were for some reason unoccupied.

A monkey-like creature with no legs?


How will one stake Ether?

Question: Once Ethereum makes the switch to proof of stake how will one choose to stake Ether? Will they have to use a special program or will Ether not in use be considered staked and be used to gain more Ether?
Answer: After moving to Casper POS, To become a validator (mine new ethers) you will need locking up an amount of your ethers (to be bonded) by sending them to the Casper contract. If i remember they will stay locked for 4 months.
Answer: The Ethereum Launchpad has the instructions for staking:
https://launchpad.ethereum.org/
The launchpad informs you of the requirements, including running one of the Lighthouse, Nimbus, Prysm, Teku clients.
The ETH Staker community is highly recommended.  They are very knowledgable, but their first value is "Welcoming First, Knowledgeable Second":
https://ethstaker.cc/

How will one stake Ether?


When is the union of topologies a topology?

Question: The union of two topologies on some set may or may not be a topology. When is it a topology?
Comment: Here's an obvious sufficient condition: when one is contained in the other. But that's not a necessary condition.
Comment: I'd very much doubt there's any non-trivial condition, you would have to check these kinds of things on a case by case basis.
Comment: If $X$ has cardinality one or two then this result is true, otherwise it is false.  https://proofwiki.org/wiki/Union_of_Topologies_on_Singleton_or_Doubleton_is_Topology
Answer: Let $\tau_1$ and $\tau_2$ be two topologies on a point set $X$.  That is, $\tau_1$ and $\tau_2$ are subsets of the powerset of $X$, each indicating which subsets of $X$ should be called open.  Let $\tau = \tau_1 \cup \tau_2$.  In general $\tau$ is not a topology on $X$, but let's see which conditions are satisfied and which could fail:
(1)  $\emptyset \in \tau$.  True since $\emptyset \in \tau_1$ (and $\tau_2$).
(2)  $X \in \tau$.  True since $X \in \tau_1$ (and $\tau_2$).
(3)  Arbitrary unions of open sets are in $\tau$, that is,
$$\bigcup_{\alpha \in \mathscr{I}} U_{\alpha} \in \tau.$$
Not true in general.  At best, I can partition the sets into those in $\tau_1$ and those in $\tau_2$ so that we have:
$$\bigcup_{\alpha \in \mathscr{I}} U_{\alpha} = \bigcup_{\alpha \in \mathscr{I} \cap \tau_1} U_{\alpha} \cup \bigcup_{\alpha \in \mathscr{I} \cap \tau_2} U_{\alpha} = V \cup W,$$
where $V \in \tau_1$ and $W \in \tau_2$ because each $\tau_i$ is a topology.  But here's where we get stuck.  I have no guarantee that $V \cup W$ is in either $\tau_1$ or $\tau_2$, hence I can't place $V \cup W \in \tau$.
(4) Finite intersections of open sets are in $\tau$, that is,
$$\bigcap_{i=1}^n U_i \in \tau.$$
Again, I could partition the sets according to $\tau_1$ and $\tau_2$ so that
$$\bigcap_{i=1}^n U_i \in \tau = V \cap W,$$
for $V \in \tau_1$ and $W \in \tau_2$.  But unless $V \cap W \in \tau_1$ or $\tau_2$, I cannot find $V \cap W \in \tau = \tau_1 \cup \tau_2$.
So this leads to the necessary (and sufficient) conditions:  $\tau = \tau_1 \cup \tau_2$ is a topology if every pairwise union $U \cup V$ and intersection $U \cap V$ of open sets $U \in \tau_1$ and $V \in \tau_2$ lies in either $\tau_1$ or $\tau_2$.  Of course, this does not strike me as a very useful or easy condition to check.
Comment: @SamBlattner The set $\mathscr{T}_{1} \cup \mathscr{T}_{2}$ consists of all \textit{sets} in $\mathscr{T}_{1}$ or $\mathscr{T}_{2}$. When one considers whether $V \cup W$ belongs to this union, we evaluate whether one of $\mathscr{T}_{1}$ or $\mathscr{T}_{2}$  contains $V \cup W$. You are mistakenly thinking (methinks) that one must evaluate whether, if $\mathscr{T}_{1} = \{ T_{1}, T_{2}, \dots \}$ and $\mathscr{T}_{2} = \{ T'_{1}, T'_{2}, \dots \}$, $V \cup W \in \{ T_{1} \cup T'_{1}, T_{1} \cup T'_{2}, \dots, T_{2} \cup T'_{1}, T_{2} \cup T'_{2}, \dots \}$
Comment: Thanks for the reply. I was looking for an useful necessary and sufficient condition, but this makes me think there is no such thing.
Comment: I understand completely the failure of condition (4), but I don't understand the failure of condition (3). Do you think you could explain it? By definition $V \in \mathscr T_1$ and $W \in \mathscr T_2$, which seems like it should by definition of unions imply that $V \cup W \in \mathscr T_1 \cup \mathscr T_2 \equiv \mathscr T$...? Or am I mistaken?
Answer: Years late to answer this but:
There is actually a problem in Munkres related to this: prove for a family of topologies $\{\tau_\alpha \}$ on a set $X$ that there is a unique smallest topology containing all of the topologies in the family.
If you set $S = \{ U : U \in \tau_\alpha \text{ for some } \alpha \}$ and consider the topology generated by $S$ (as a subbasis) I think this does the trick.  It also provides a less wordy sufficient and necessary condition to your question.


Tiling shower walls how and where to start

Question: I'm about to start tiling my shower walls I just don't know where to start or how, I've never tiled before my shower is 5ft in length 32 inches wide and 80 inches high I have chosen a 12 by 24 inch tile but got 10 by 16 inch tiles I got everything I need for the job just need advice for starting and laying the tiles
Comment: Hello, and welcome to Home Improvement. Unfortunately, this is too broad for our Q&A format. Please take our tour to see how better to contribute here.
Answer: If both corners are equally visible the best way is to start in the middle plumb on center. As you get to the corner measure and cut to fill. The leftover peice is the size of your starter for the next wall. Draw a new plumb line on the short wall according to off cut. This method does not always work out. If you end up with a tiny piece in the corner, offset your center line until visually appealing.
If your tile is 16 wide it would work out like this

Your short starter peice on the short wall would be about 5-1/2 inches
Starting at one corner is much easier but real professionals will normally start on center.
Comment: +1 for adjusting the starting point until "visually appealing".
Comment: That's exactly what I got, nice much respect
Answer: Best place to start is on the bottom of the largest wall. Start in the corner that will be seen most. This will be your "pretty" corner. Finish that wall and then start at the bottom corner of the smaller walls and work up and out. You can save all your cutting till the end of each wall or cut as you go up. This also might depend on you laying pattern and how good you think you can slide them in. Some people measure and cut all at once before starting, some cut as they go, and some do all the wall row end cuts when finished with the wall. Your last 2 walls can be done at the same time. Make sure, if you precut, to include grout lines in your calculations.
Comment: Fine to start in a corner but you should check how close your grout lines will be to the other edges. You don't want to get to the other side or the top of the shower and realise you need a narrow sliver of tile to finish it. If that's going to happen, start with a half or 3/4 tile instead of a whole one. If there are any other features in the shower that will need tiling around you might want to check where those will end up in relation to the grout lines too.


In what context would one think a cone surface is not a smooth manifold?

Question: Here the cone surface is $C:=\{z^2=x^2+y^2,\, z\ge 0\}$ in $\Bbb R^3$. Sometimes it is said $C$ is not a 2-dimensional smooth manifold. Talking about manifolds without specifying the atlas is meaningless, of course. However, it's pretty easy to see that under many atlases, for example any atlas that's compatible with the atlas containing the projection to the $xy$-plane as the only chart, $C$ will indeed be a smooth manifold. So I wonder, in what "usual" context (topology, atlas etc), would anyone possibly regard $C$ not as a smooth manifold?
Comment: @mathreadler that's a reasonable guess. However, if one equips it with a nice chart like projection, there'll be nothing special about the peak.
Comment: If one accepts the premise of your question, would there be any manifold at all that is not smooth? For any point or region of non-smoothness one could simply pick a chart in which it looks smooth.
Comment: I see. The proper term should be "an embedded submanifold in $\Bbb R^3$". Thanks. @Rahul
Comment: Uhm, it's not differentiable at the peak, I guess?
Comment: I have not heard about these charts. They sound fishy. I could imagine you approximate the surface by some sequence of functions getting arbitrary close in some sense and still being differentiable there for all manifolds in that sequence. But I don't know if that is what charting means.
Answer: It is not a smooth manifold in the sense of the differentiable structure it inherited as a subspace of $\Bbb R^3$. For instance, the smooth function $f:\Bbb R^3\to\Bbb R$ given by $(x,y,z)\mapsto z$ is not differentiable as a function on the cone.
To elaborate a bit, a subset $S$ is an embedded $n$-dimensional submanifold of an $m$-dimensional manifold $M$ iff there for every $s\in S$ exists an open $U\subseteq M$ with $x\in U$ and a chart $\phi:U\to \Bbb R^m$ such that $\phi(U\cap S)$ is an $n$-dimensional hyperplane in $\Bbb R^m$. In that case, the different charts $(\phi|_{U\cap S}, U\cap S)$ may be extended to a maximal atlas on $S$, and this is the differential structure that $S$ inherits from $M$. There is no such thing for the tip of the cone in $\Bbb R^3$.
Comment: Thanks. Could you elaborate a bit on the differentianle structure inherited from $\Bbb R^3$. Can it be easily defined?
Answer: An elementary property (that is often needed) of smooth manifolds is the tangent space at each point, which is obtained by taking derivatives of curves. Consider any curve on $C$ that passes through the peak. This curve is not differentiable at the peak (you can consider it as a curve in $\mathbb{R}^3$), hence we are missing a tangent space at this point.
Comment: why the curve is not differentiable at the peak?
Comment: Just consider a 1-d curve which has a similar peak. It's not possible to put a well defined tangent at that point, the limits for the differential quotient from right and left are different.
Comment: $C:(x,y,z):z=\sqrt{x^2+y^2}$  suppose it is a smooth manifold meaning there exists a smooth parametrization$ φ(u,v):U⊂R2→C$ such that $φ(u,v)=(φ_1(u,v),φ_2(u,v),φ_3(u,v))$ such that $φ_3=\sqrt{φ_1^2+φ_2^2}$ being continuously differentiable at every point but it fails at the peak since the limit at the peak of the derivative fails to be unique because if i approximate it through different paths(curves) it will be different. (So which is the the derivative and what limiti to take to continue my proof.?
Comment: I give you a hint: consider a curve on there being like $x \mapsto -\vert x \vert$ (intersect a plane with the cone). This is clearly not differentiable at 0.
Comment: What should be the tangent space at the peak? What are tangents at the peak? They are not defined there.
Comment: thats what i ask .
Comment: ok ! thank you.
Comment: Can you help me to write down the exact math?
Comment: https://math.stackexchange.com/questions/2902120/proving-the-cone-is-not-a-smooth-surface here if you can help.
Answer: For surfaces in $\mathbb{R}^3$ there is also an equivalent geometrical property that some set is a surface (smooth submanifold of dimension 2, without border) if and only if locally it can be represented by a graph of a smooth function. It means, locally your surface has a form:
$$
 x = f(y,z) \text{ or } y = f(x,z) \text{ or } z = f(x,y),
 $$
where $f$ is some infinitely smooth function. This comes from the fact that
if you have general parametrization $p(u,v) = (x(u,v), y(u,v), z(u,v)), \, (u,v)\in U,$
where $(u,v)$ is the parametrization, then the differential of $p$ is injective (by definition of a surface). Injectivity of $p$ will imply that matrix of the differential will have rank 2, which says that locally you parametrize your surfrace by some pair $(x,y)$ or $(y,z)$ or $(x,z)$.
Then you need to work a little with the implicit function theorem to obtain
the formula above.
For the case of the cone it becomes obvious. The only way to choose coordinate system so that surface near the peak is a function, is to choose
that peak "looks up". But in this case the obtained function is necessarily not smooth, hence it cannot be a surface.
Comment: peak looks up? and why it is not smooth?
Comment: "looks up" it means the tip of the cone looks in direction z and the function is a function of (x,y). in this case the derivative (or gradient) will have a jump at tip. Again, it is important that (x,y) is not just a parametrization of a surface of a cone, but the cone is embedded in R^3
Comment: I can see the image but i cannot write the math
Comment: https://math.stackexchange.com/questions/2902120/proving-the-cone-is-not-a-smooth-surface/2902134#2902134
Comment: If you assume that the statement above is true (which you need to prove of course), then at the vicinity of the tip your function can be represented only and only by sqrt(x^2 + y^2), (x,y) near 0 (because the statement above is for global coordinates (x,y,z)).


Eclipse reload Launch configuration files

Question: I am editing the launch configuration in the folder WORKSPACE/.metadata/.plugins/org.eclipse.debug.core/.launches/. Is there any way to force the eclipse reload the changes in these files? I need this because I need fix the broken configurations from previous version of eclipse. I wrote a plugin which can do this, but I need to restart eclipse after that. Does anyone know how to this without restarting eclipse? Thanks
Answer: I would rather export those "launches configurations" within my project.
(See "How do I save Eclipse launch profiles across workspaces?": choose a shared file location inside your workspace from the "Common" tab of the launch configurations.)
I usually keep them in <project>/.settings.
Then, if you do modification from an external editor, you can simply refresh your project, and it should pick up the evolutions in said configuration files.
No restart needed:
You don't need to read again your workspace, which contains metadata about your project.
You only need to refresh your project, which contains data, ... and now also those configuration files.