Why is my dishwasher causing the dishes to have an odor?

Question: I have a GE Profile Triton XL dishwasher and the dishes come out clean but have an odor to them, it's a metallic/sour smell.  Any idea on the proper way to clean it?  There is no built in clean cycle.  There's no food trap either (as far as I can tell).
Answer: Dishwasher cleaners are available - I use this one every six months or so - it has a range of chemicals in it which get in around all the bits that might be moldy and gives them a good clean.
Once cleaned, the following tips I found over at wikihow will help prevent this in future:

Run the garbage disposal before starting the dishwasher. The dishwasher drains into the same pipe as your sink, so that drain must be clear.
Run a bit of hot water in your sink before running the dishwasher. You will get cleaner dishes if the water starts hot. You can collect the water you run and use it for watering plants or other purposes. Run the water until what comes out of the tap feels hot.
Make sure your water starts hot enough. Set the thermostat on your water heater to 120F (50C). Water that is cooler than this won't do a good job cleaning. Water that is hotter could scald.
Load your dishwasher properly, stacking items facing downward and inwards. Check that all the arms can spin freely before running the dishwasher.
Run full loads to conserve water and energy, but don't pack dishes too tightly. Dishwashers wash dishes by spraying water over them, so the water needs to be able to get to the dishes to clean them.
Don't wash containers with labels that could come loose. Scrape heavy debris and large particles off dishes before placing them in the dishwasher.
Don't pre-rinse too much. Dishwashers and detergents have both improved. If you haven't tried putting dishes in dirty lately, try it again. You may be pleasantly surprised.
Not all dishwasher detergents work the same. The next time you buy a new container of detergent, try a different brand and see if you get better results. Look for ratings and reviews, too. At the very least, favor powders and tablets over gels and liquids, and keep them dry and free of excess moisture prior to use.
Wash small items in the basket with your forks and knives so they don't slip through the racks and end up in the bottom. Some dishwashers even have enclosed baskets just for small items.
For dried-on gunk, get the area wet or spray the cleaner, then let it sit and dissolve for a few minutes before wiping. You'll save yourself a lot of scraping and scrubbing.
Answer: I had this same exact problem. Then I noticed that if I poured water out my sink faucet (which was also connected to the line going to the dishwasher), that it had this funny smell too. It was almost like sulphur, but you had to know to smell it or you might not notice it.
I then smelled my ice cubes and they didn't have this smell.
The problem also went completely away in the winter, then came back after the thaw.
The cause? Yeah, turns out the faucet had two issues. One was the hose attachment to it would trap water in it. So, I removed that. I then cleaned the faucet parts and piping with bleach, then rinsed thoroughly, and put it all back together again. This lasted for about 2 months, and then the smell came back. That's when I learned from my dad that some delta-type faucets trap water in them. I replaced the delta-type handle faucet with a dial-type, and the problem went away because the faucet wasn't trapping water.
Anytime you have trapping water in the line or some part of the line, it breeds smelly bacteria that spreads to other parts of that line.


Why doesn't the Bitcoin blockchain truncate past data?

Question: AFAIK, verification of transactions on the blockchain doesn't require the full chain data and six to ten verification will be enough (which makes uses of a Merkle tree). Thus, why cannot it abridge the data for a future complete node?
Comment: I think it's healthy to re-ask questions since that one was asked more than 2 years ago.
Comment: @LucaMatteis: The situation hasn't changed from when that question was answered. The protocol of Bitcoin still works the same.
Comment: @GregHewgill I found not technique detailed description on this. It seems I have to read source code.
Answer: The idea of Bitcoin is that you can obtain the current state of the network without having to trust anyone. You essentially rely on the fact that the state that has most work put into it, is the valid state, and that all transactions are chained together up until the genesys block, after which there are no more transactions.
Now if you were to truncate this state (the block chain) in half, you could hard code this information into the software and it could reach some form of consensus among the nodes of the network. However this opens the door for attacks, because a dishonest node could easily fake and send you a wrong block height information, perhaps making you believe that a different history happened before the truncation of the block chain. And it could do this by simply broadcasting chunks of the history that was truncated, because lots of work has been put in that chunk and your client is programmed to accept longest worked on chains.
You would really have no way of knowing unless you read the entire history yourself.
Comment: Thanks, but I should ask in a more concise way that I'd like to dip into tech details. If mining is not involving/safe enough to do without actual history records in blockchain we can clean up the history redundancy. The only question is here that I do not know how the merkle tree is generated. Can anyone explain me an abstract model that takes in (previn) and outputs (stdout), showing in a diagram?
Comment: No, nobody could fool you.   If you truncate the chain a year ago, saving the aggregated state, and the old block hash, all you'd need to do is ignore anything that doesn't hash to the longest chain, offset by your truncation.   There's no way a fork can reach back a year, so you're good.   Clients do this all the time.   And since you reached your *own* conclusion and cache state... you didn't have to trust anyone to do it.


Four (4) Form On-Boarding Process

Question: My mobile application has an onboarding process comprised of 4 screens/forms.  The forms have 3, 4, 2, and 7 questions.  What is the industry standard user experience:  (1) saving data at each screen and allowing the user to complete the onboarding process where he/she left off at a later time or (2) having the user complete all the forms and if he/she does not complete the 4 forms, he/she begins at the beginning until he/she completes the forms.
Comment: Depends on your audience and the complexity of the questions.   As a user, can I easily complete the form quickly, despite having to answer 16 questions?   Also, is this for a captured audience (i.e. company employee who must register) or an optional (access to the site/application)?
Comment: The onboarding is for access to a mobile application for consumers.  A user can easily answer the questions.
Comment: Based on that, I definitely agree with choice 1, particularly when the last form has the most number of questions.   I might have no problem answering the first forms, but when the last one looks more complicated (7 questions when previous form had 2), I might step away for a bit.
Answer: Definitely 1). Save the data in between, and organize the questions in ways that help the user chunk out the process in a logical way without feeling overwhelmed.
Answer: Save the data, allow the user to skip onboarding steps, track onboarding completeness status for users and send them a reminder: "Hey, pick up from where you left. You are almost ready to start using our app".
I was surprised by the number of people that got back on the onboarding step once they received emails that stimulated them to finish.

Four (4) Form On-Boarding Process


Can a Finney Attack make SatoshiDice betting profitable?

Question: Can a Finney Attack make SatoshiDice betting profitable? If you perform a Finney Attack whenever your bet fails (by replacing it with a transaction to yourself), then would it make betting profitable, even though the Finney attack won't always work? How much mining power would you need to break even on profitability?
Answer: The short answer is: yes, but it would not be profitable in the long-term.
A Finney Attack is not easy to pull off, because guessing when the rogue miner's block will be generated is imprecise and inaccurate. Guessing gets easier with the more hashing power the rogue miner puts on the network, but you probably won't see real profit unless you get a pool to participate in your attack.
Comment: Satoshidice bets pay out within 30 seconds or so, so you can just bet after you find a block.
Comment: Good point, I hadn't thought of that. That would mean one can make a profit with this attack at any amount of hashing power, as long as they're making a profit mining regularly anyway.


how to get rid of "unexpected token 0 in JSON at position 0"? which time this error is actually shown? What's the major reason to show this error?

Question: First of all, please don't criticize me. I am beginner and I started to learn the server and working on it. But almost all the time I regularly found this error. I search this question and want's to know properly about it. But now I am becoming more confused because I don't know the major reason of showing this error. So, Please help me. As a beginner, It is the only errors that frustrates me a lot.
In the command Line I found this error
SyntaxError: Unexpected token 1 in JSON at position 0
    at JSON.parse (<anonymous>)
    at createStrictSyntaxError (C:\Projects\book-stock-server\node_modules\body-parser\lib\types\json.js:160:10)
    at parse (C:\Projects\book-stock-server\node_modules\body-parser\lib\types\json.js:83:15)
    at C:\Projects\book-stock-server\node_modules\body-parser\lib\read.js:128:18
    at AsyncResource.runInAsyncScope (node:async_hooks:199:9)
    at invokeCallback (C:\Projects\book-stock-server\node_modules\raw-body\index.js:231:16)
    at done (C:\Projects\book-stock-server\node_modules\raw-body\index.js:220:7)
    at IncomingMessage.onEnd (C:\Projects\book-stock-server\node_modules\raw-body\index.js:280:7)
    at IncomingMessage.emit (node:events:402:35)
    at endReadableNT (node:internal/streams/readable:1343:12)

In the Client Side, I basically want's to decrease quantity 1 by 1 by clicking (handleDelivered) button and sent the quantity as a request to the server to store the quantity in MongoDB database. But when I implement this functionality it doesn't work and shows that error in the command line.
    const handleDelivered = () => {
        const updatedQuantity = { quantity: quantity - 1 };
        const url = `http://localhost:5000/books/${id}`;
        (async () => {
            try {
                const res = await fetch(url, {
                    method: "PUT",
                    headers: {
                        'Content-type': 'application/json'
                    },
                    body: JSON.stringify(updatedQuantity.quantity)
                })
                const data = await res.json();
                if (data.modifiedCount >= 1) {
                    setbookInfo({ ...bookInfo, quantity: updatedQuantity.quantity });
                }
            }
            catch (err) {
                console.error(err);
                toast.error("There was a server side error");
            }
        })();
    }

Here in the server side I did exactly to store the quantity in the database and send the response to the client
            const id = req.params.id;
            const updatedQuantity = req.body;
            const filter = { _id: ObjectId(id) };
            const option = { upsert: true };
            const updatedDoc = {
                $set: {
                    quantity: updatedQuantity.quantity
                }
            };
            const result = await bookCollection.updateOne(filter, updatedDoc, option);
            res.send(result);
        })

Answer: This is caused by body-parser.
On this line it says:

      if (first !== '{' && first !== '[') {

… but the JSON specification was changed, years ago, to allow the top level data type in a JSON text to be any kind of JSON data and not just an array or object.
You are sending a number as your top level JSON data type, which is allowed by the current JSON specification, but which causes body-parser, in its default configuration, to throw an error.

You can change body-parser to support the current spec with a configuration option:

strict
When set to true, will only accept arrays and objects; when false will
accept anything JSON.parse accepts. Defaults to true.

Alternatively, a work-around would be to send an object instead of a number:
body: JSON.stringify(updatedQuantity)

You would need to change the server side code to read req.body.quantity instead of req.body


Request to burninate the tag "Puree"

Question: That tag is strange, while looking for a tag "purifying" that tag shows up. And I don't really know the purpose of that tag. Currently there are no questions under that tag.
https://cooking.stackexchange.com/tags/puree/info
Comment: Cary, one more thing if you are not aware how Meta works: The downvotes here mean "I disagree with your suggestion" (so people think the tag should stay), not "It's a bad question". To your best knowledge, the tag did not mean anything, so it was a good thing to start a discussion about it. Don't be discouraged by the downvotes, they are used differently on Meta than on main.
Comment: Just a note, it's both a verb and a noun. If you put broccoli in a blender, you are pureeing the broccoli. The resulting product is broccoli puree.
Comment: There are four questions tagged "puree" - http://cooking.stackexchange.com/questions/tagged/puree?sort=newest Did you mean no one has tagged anything "purifying"?
Comment: @rumtscho, I didn't know that! Thanks for the information! Yeah, I will not be discouraged. Thanks again Sir.
Answer: I don't see a reason to remove it. Just because nobody has thought of using it doesn't mean that nobody will do so in the future. And I see no red flags with it - it is not suffering from homonym problems, or from being a meta-tag.
Is it possible that there is a language issue? Puree is a culinary term used for mashed vegetables, but if you have not heard it, maybe you thought that it is not a real word? I admit that it is somewhat uncommon in English.
Comment: Tags can't exist without being used on questions - but as it's been pointed out, there are actually four questions with the tag, which is more than enough to keep it out of purgatory.
Comment: Aaronut is correct in principle. There is one exception: when a question with the tag is created and later deleted. In this case, the tag continues to exist for a few months, after which it is automatically destroyed. So it's not completely impossible to find a tag without questions for it, although very rare.
Comment: Yes, exactly. I've not heard it. I was thinking that it is a mistake. Thanks!
Comment: @rumtscho, thanks! very informative. I really appreciate for helping me.
Comment: I think it is also the canonical name for a component in certain platings?
Comment: @rackandboneman I have never heard it used for anything which was not made from mashed vegetables or fruit. If you have examples for a different usage, I'd love to see them and educate myself.
Comment: It seems to be a standard  in all these swanky fish dishes presented on masterchef and stuff, so I assumed it was also a formal term for whatever is used to keep the fish from sliding off the plate...

Request to burninate the tag "Puree"


Mysql tables crashing after each XAMPP restart

Question: XAMPP version: 7.3.7
Operating system Windows 10
Each time when I restart XAMPP random mysql table crashes.
Video here
https://www.youtube.com/watch?v=tR_OTxmPIP4&feature=youtu.be
I've been having this problem for weeks and wasted many hours trying to prevent that from happening. This is happening on both of my PCs.
I have tried to repair it with a command I found "mysqlcheck -u root --databases mysql --auto-repair --use-frm" and it works, but each restart same thing happens.
I also tried restoring tables from backups. Same thing, it does it's job repairing it, but when I restart server another table gets corrupted.
My questions are:

What can I do to fix it?
Am I doing something wrong?
Is there a proper way to exit mysql server?
If this isn't my or my computer's fault what version of XAMPP is free from this problem?
Answer: It seems like the problem is solved in the latest XAMPP version. (7.3.8)


ASP.NET web service timeout

Question: I have a ASP.NET asmx web service which times out.
I see that IIS has couple of places where the timeout setting can be defined.
I also know that the timeout setting can be defined in the web.config file using the "httpRuntime" element.
I also see that the app pool the service runs under has its own timeout setting
I am not sure why Microsoft has chosen to have timeouts at multiple levels even though they would end up affecting the web service as a whole. (other than in case of the app pool, where multiple applications can be run under)
Can someone please help me understand which one has precedence?
Answer: on the service server side, try setting this in config:
<code><httpRuntime executionTimeout="1200"/>
</code>

ASP.NET web service timeout


Number of features vs. number of samples : if small sample size is sufficient, why take large number of samples?

Question: As a newbie, I am a little confused. I have a dataset for binary classification with 11 features and 102 sample data. I have seen in most places (e.g., kaggle competions), the dataset may have hundreds of thousands of data samples for tens of features. On the other hand, this paper says (at least for LDA classifier) optimal number of features is n-1 for a sample size n. My question is, if small no. of samples is enough (or even optimal), why care for larger samples? What am I missing here?
Comment: The class boundaries may lie on a manifold, requiring more data to estimate. It's rare for real data to be neatly separable by hyperplanes in the raw feature space. With such a small sample you're going to have to use one of those simpler models, though, othewise you will overfit.
Answer: Bounds on the needed amount of samples are very common in PAC learning.
When you define a concept class you can compute a minimal size set of sample that will enable learning.
However,

More samples will allow improving accuracy
More samples will enable learning more complex concepts, that might fit your data better.
As @Emre wrote, real life data sets usually are not clean as in PAC learning. The concept class is not given to you, the data has noise and a given distribution is not guaranteed.

Showing that a classifier can be learnt with a small amount of data is great.
It is a big advantage of the learner.
However, more data usually helps and if it helps more than expected for such a classifier, it is possible that the classifier requirements doesn't hold.
Answer: Just to amplify @Dal's excellent answer, you certainly can fit models with small sample sizes. That's exactly what classical statistics attempts to do, often with success. But there is a price in terms of quality of the data
, simplicity of the model and experimental design. For example, to estimate interaction terms efficiently and credibly, you want to randomly apply the treatment effects. Machine learning typically occurs in observational data where none of these assumptions are correct.
That said, 102 samples is way to small in a problem with 11 variables and a binary outcome. Classifications typically take more data than regression problems (continuous outcome). That's why you often hear pollsters using 1000 respondents to predict a categorical outcome on the basis of one or two features (questions).
There is an optimistic rule of thumb that one needs 10 variables for each parameter that one wants to estimate. I have always thought this was a bit thin, but even on that measure, your sample is too small.
Comment: "Classifications typically take more data than regression problems" - can you kindly refer any paper on this?


How to get the transform the coordinates of a 3D point from the standard basis to another basis?

Question: Suppose I have the coordinates of a point in the standard $\mathbb{R}^3$  basis $B_0 = (\vec{e_0}, \vec{e_1}, \vec{e_2})$, with $\vec{e_0} = (1,0,0)$, $\vec{e_1} = (0,1,0)$ and $\vec{e_2} = (0,0,1)$.  Let $B_1 = (\vec{u}, \vec{v}, \vec{w})$ be my target coordinate system and $P_{B_0} = (x, y, z)$ the point I want to get the coordinates of in $B_1$. Could anyone explain to me how to do this? This is what I want to achieve (finding $x'$ and $y'$) but in 3D.
Comment: this: [3 dimensions matrix rotation](https://en.wikipedia.org/wiki/Rotation_matrix#In_three_dimensions) ?
Comment: Yes, I know about that and I even slightly understand how it works. But I'm having trouble making links here for actually solving my problem. Let's take $x$ axis rotation for example: I have my $\vec{u}$ vector which is a rotated $\vec{e_0}$, but I do not know by how much, if that makes any sense.
Comment: To answer the title question, find the coordinate transition matrix. Each standard basis vector is rotated by $\theta $ so need to simply find the image of each of these.
Comment: Yes, you need the angle between the 2 and using the matrix in the link I sent you will get it
Comment: I know $\vec{u}$, $\vec{v}$ and $\vec{w}$ (each of their components). Do you think I can find the angle between, say, $\vec{e_0}$ and $\vec{u}$ like so: $arccos(\frac{\vec{e_0} \cdot \vec{u}}{e_0 \cdot u})$?
Answer: If you make a matrix $M$ with the basis vectors $u$, $v$ and $w$ as columns. Then you can map from the standard basis to the new one by transforming your vector with $M$.
You can also send vectors from the new basis back to the standard basis by transforming them with $M^{-1}$.
If $M$ happens to be a rotation matrix (as shown in the pictute) then also then $M^T = M^{-1}$
Comment: So all I have to do is to multiply $M$ by the column vector $(x, y, z)$? Because I have $M = (\vec{u}, \vec{v}, \vec{w})$.
Comment: Yes, I think so
Answer: Let the new coordinates be $(X,Y,Z)$, so that
$$\vec P=X\vec u+Y\vec v+Z\vec w
\\=X(u_x\vec e_0+u_y\vec e_1+u_z\vec e_0)+Y(v_x\vec e_0+v_y\vec e_1+v_z\vec e_0)+Z(w_x\vec e_0+w_y\vec e_1+w_z\vec e_0)$$
at the same time that $$\vec P=x\vec e_0+y\vec e_1+z\vec e_2.$$
By identification,
$$\begin{cases}Xu_x+Yv_x+Zw_x=x,
\\Xu_y+Yv_y+Zw_y=y,
\\Xu_z+Yv_z+Zw_z=z.
\end{cases}$$
Now you can express the new coordinates as a function of the old ones by solving the $3\times3$ system.
Answer: After testing my program with a few examples, I might have found the solution based on one of the comments to my original post. I have the standard $\mathbb{R}^3$  basis $B_0 = (\vec{e_0}, \vec{e_1}, \vec{e_2})$, with column vectors $\vec{e_0} = (1,0,0)$, $\vec{e_1} = (0,1,0)$ and $\vec{e_2} = (0,0,1)$ as the source coordinate system ($O$ being its origin) and $B_1 = (\vec{u}, \vec{v}, \vec{w})$ as the target coordinate system ($\Omega$ being its origin) with $\vec{u}$, $\vec{v}$ and $\vec{w}$ that are known. In order to get the coordinates $x'$, $y'$ and $z'$ of point $P(x, y, z)$ within coordinate system $B_1$, follow these steps:

Translate the point with $-(\vec{O\Omega})$ (would correspond to considering that the target coordinate system has its origin in $O$).
Calculate the the rotation angles between each axis of the source system and its corresponding axis in the target system, knowing that $\angle(\vec{u},\vec{v}) = \arccos(\cos(\angle(\vec{u}, \vec{v}))$ and $\cos(\angle(\vec{u}, \vec{v})) = \frac{\vec{u} \cdot \vec{v}}{||\vec{u}|| \cdot ||\vec{v}||}$.
Apply successive $x$, $y$ and $z$ rotations to the translated point using previously obtained angles.

Let me know of any inaccuracies that may have been posted above.


Calendar view in iPad Mini running iOS 9

Question: I can't seem to adjust my calendar view to see 5 days under the week view with my iPad Mini running iOS 9.  How do I change the setup?  I don't see an option in settings.
Answer: The few things you can change in the native calendar app are under settings at the bottom of Mail, Contacts, Calendars:

You would need to download a custom calendar app to change the week view of your calendar data. The best I can manage is changing the week start date, which changes things everywhere.


Is it possible to only shuffle a few specific stations on Pandora?

Question: I have a plethora of different types of stations on my Pandora and wanted to only shuffle a few of them together when I listen. Is there a way to do this?
Answer: In the web interface you can do this by selecting "Shuffle", then underneath select the little arrow in the yellow box next to "Shuffle All" (or possible "Shuffle <genre>"). Then select "My Shuffle".
Once you've done this, all your stations should have a checkbox next to them. Simply check or uncheck the ones you do or don't want as part of your mix.
Answer: Yes. On the app, swipe to the left at the "Shuffle" button and a pencil will appear. Click the pencil icon and it will allow you to pick which stations to shuffle.
Answer: In the Android app, you can hold-tap a station and choose Add Variety to add another band to it.  You could also rename it after that.


hanging a water hose holder on stucco... do I need to find a stud?

Question: I am hanging a water hose holder for a 50 foot all-rubber hose.  This holder can be mounted with 6 screws (2 rows X 3 columns).  Would it be necessary to try to at least get that middle column attached to a stud or should standard wall anchors be sufficient?
Answer: I would recommend just getting a stand. Once you get through stucco it's not sealed and moisture and air gets in and causes rotting behind the stucco.
Most carpenters and cladders may tell you to just spray foam or some sort of sealant will do the trick. But I am a restocking specialist, I have the carpenter and fire flood and mold restoration experience. I tell you to think of it deeply, the stucco acts like cement it stretches and shrinks there for once the sealant is cracked it's not going to expand or shrink with the stucco.
Some will tell you to fill it with stucco. But again unless you are the one who installed it to know the exact brand that was originally used there is different ingredients in different brands meaning again expansion and shrinkage are all off set. I know alot of people won't think it really matters one little hole. But moisture once behind the stucco becomes drops that can infiltrate the tightest spots and go far. Rotting everything behind it.
But that's just my 2 cents based on almost 2 decades of experience dealing with this stuff.
Answer: Yes, you want to find a good solid stud to anchor into, because if the teenage animals that you live with are anything like the teenage animals that I live with they will not be kind to it.
The stucco is not strong enough to support anything...
(BTW, you can probably find a good stud under each side of your windows.)
Answer: This hose is not that heavy but yes you should try and hit 1 stud. 1 stud would easily support the weight. But what type of siding / sub siding?  In some homes pre 50's with a sub siding of angled 1" I would not worry about hitting a stud. If a more modern home with ? Sub siding I would want to hit a stud on 1 point wether right left or center. I have seen some homes that had no sub siding because the wrap and exterior siding met code in the 70's I would absoulty want a stud in this case because there were thousands of siding failures in my area mostly the vinyl clad chip board and that stuff has no strength 25 years later and many houses had to be resided with some $ from class action lawsuits , but it will be best to hit at least 1 stud if possible. Since you have stucco what is the base, some are just chicken wire, prior to the 50's many were built with expanded steel lath , if that kind of exterior 3 rows by 2 would be fine, chicken wire stucco hit a stud or the first time you pull on the hose you may be shocked at the damage.


What is the difference between dynamic programming and branch and bound?

Question: I only know that by branch and bound, one can REDUCE the procedure to obtain a solution, but that only helps for problems which have a solution space tree.
Answer: Dynamic Programming
Dynamic programming (usually referred to as DP ) is a very powerful technique to solve a particular class of problems. It demands very elegant formulation of the approach and simple thinking and the coding part is very easy. The idea is very simple, If you have solved a problem with the given input, then save the result for future reference, so as to avoid solving the same problem again. Shortly 'Remember your Past' .
If the given problem can be broken up in to smaller sub-problems and these smaller subproblems are in turn divided in to still-smaller ones, and in this process, if you observe some over-lappping subproblems, then its a big hint for DP. Also, the optimal solutions to the subproblems contribute to the optimal solution of the given problem ( referred to as the Optimal Substructure Property ).
There are two ways of doing this.

1.) Top-Down : Start solving the given problem by breaking it down. If you see that the problem has been solved already, then just return the saved answer. If it has not been solved, solve it and save the answer. This is usually easy to think of and very intuitive. This is referred to as Memoization.
2.) Bottom-Up : Analyze the problem and see the order in which the sub-problems are solved and start solving from the trivial subproblem, up towards the given problem. In this process, it is guaranteed that the subproblems are solved before solving the problem. This is referred to as Dynamic Programming.

Branch And Bound

A branch-and-bound algorithm consists of a systematic enumeration of candidate solutions by means of state space search: the set of candidate solutions is thought of as forming a rooted tree with the full set at the root.
The algorithm explores branches of this tree, which represent subsets of the solution set. Before enumerating the candidate solutions of a branch, the branch is checked against upper and lower estimated bounds on the optimal solution, and is discarded if it cannot produce a better solution than the best one found so far by the algorithm.

For more Information About Branch and Bound Please refer this link :
http://www.cs.umsl.edu/~sanjiv/classes/cs5130/lectures/bb.pdf
Answer: Dynamic programming requires a recursive structure (a.k.a., optimal substructure in CRLS).  That is, at a given state, one can characterize the optimal decision based on partial solutions.
Branch and bound is a more general and is used to solve more difficul problems via implicit enumerations of the solution space.


Why is it recommended to close all programs before installing a new program?

Question: What kind of problems arise from installing a new program while other programs are running?  I'd imagine the GAC solved a lot of the old problems of shared dll's being locked.  So what kind of issues still arise?  I can see issues with upgrading a single program for sure, but outside of this its hard to see why apps would stomp on eachother's toe's.
Comment: This is only needed for crippled operating systems. With better systems, your can install binaries or libs while old versions are still running or in case of sshd network connections exist.
Answer: GAC only helps with .NET assemblies. There a lot of other applications which are not written in .NET.
What else problems exist?

Other applications holding files open
Other applications holding network connections open
Other applications holding devices open
Other applications slowing down the machine so that an unexpected timeout somewhere may occur leaving the work interrupted
Other applications modifying files and settings in the system the installer would expect to stay unchanged during the process (consider it transactional integrity)

Why risk failing the installation process when it is sooo easy to stop other applications and just wait out a few minutes? Go have a cup of coffee in the meantime. :)
Comment: +1 What? Theres programming outside .NET?  What is this, 2010?
Comment: In what way is it so easy to stop all other applications and then open them up again with the same configuration, so I can continue working where I left off?  Or does somebody involved expect developers to work in independent short tasks that are perfectly interruptible?
Comment: @David Thornley: You don't install things every hour do you? I for instance installed the tools I need once, made an image and haven't had major installations since months.
Comment: @Developer Art:  Not every hour, but sometimes I want to get a specific tool for what I'm working on, and sometimes one of my existing tools decides it'd like to update using an installer.  Besides, I get annoyed when I can't do stuff on MS Windows that I'd just normally do on Linux or Mac OSX.
Comment: @Brian : Correction, 2011 ;-)
Comment: I was just curious about the subject cause it would be cool to see windows or linux install programs in a virtual machine context.  If the issues are limited to the locking or other such items that can be virtualized I don't see why its not technically possible.  One could take it a step further and make installations transactional.  Just some wild thinking.
Answer: You can't overwrite a DLL or EXE that is in use by another app. The better written prompts say "look, either close stuff that is using things I want to update (and gives you a list) or continue the install and we'll have to reboot after to replace the DLL/EXE then." The lazy ones just blindly tell you to close every single thing you have running, just in case.
I hate rebooting. I hate closing stuff I'm using. Sometimes I just keep right on rolling and don't close anything that's running. I have a bit of a guess if things might share a DLL, so for example if I am updating Word I'll agree to close Outlook, but not Foxit Reader, I know they're probably independent. I pay more attention to non-lazy prompts (that tell me what the conflict involves) than to lazy ones, which may as well say "may contain peanuts" for all the thought that has gone into them.
Comment: +1 for "may contain peanuts". Also for prompts that list conflicts.
Answer: maybe the installer is just overly paranoid?
in all honesty, I have never ever closed all programs when an installer asked me to do so and never ever got into trouble. Might just be luck though.
Answer: A lot of times that message is just inserted as default text for the installation system being used. 9 out of 10 times it can be ignored. Its just that 10th time you have to worry about :-)  imo, in addition to the technical reasons DevArt summarized nicely, it was probably put in there originally so that end users dont go screaming to vendors about lost work if the installer crashes Windows and causes them to lose important spreadsheets and documents that were being worked on - a not too uncommon occurrance back in the day when installing software.
Answer: The possibility of conflict between application being installed and already running one is very small. These days most applications are based around concept of sandbox and they don't need to step out of it during installation process (or normal usage).
But lets suppose while installing some software, a change needs to be made to a file that is very likely to be already open by another application. You have two choices here:

check if the file is open/locked, figure out which process is holding a lock, display a nice dialog asking to close that specific application
just ask the person to close all the applications and you're on a safe side with no extra effort

Sadly, the second option gets picked up most of the time.
Answer: it's hedging. i never bother, and have had no trouble. the only exception is installing a plugin when the targeted app (IE, FireFox, Visual Studio, etc) is still open


Why was my question " Kiruv and outreach arguments" closed

Question: Why was this question Kiruv and outreach arguments which was originally closed, then re opened, closed again and all the comments were moved to private chat rooms?
Answer: An earlier version of the post was originally closed by the community as "Opinion-based". Two extant (at this time) comments indicate a possible rationale for this closure:

To every person a different argument works, and for some no argument. There isn't a one-size-fits-all argument. –
Harel13
Oct 22 at 4:58

Asking for the most effective is likely to be closed as it is nearly impossible to measure. You could possibly ask for some of the arguments, or since it is a complex topic, you could ask for resources discussing the topic. Entire books have been written on it –
mbloch
Oct 22 at 6:17

You edited the post, and it was re-opened by the community.
Subsequently, I reviewed the post and closed it as "Needs more focus." I believe that I was taking into account the point made in one of the above comments that "Entire books have been written on it." As the FAQ page for standard closure reasons says, "If your question has many valid answers (but no way to determine which, if any, are correct), then it probably needs to be more focused to be successful in our format."
The basic reason for pushing comment streams to chatrooms is indicated in the notice that gets posted when that happens: "Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Mi Yodeya Meta, or in Mi Yodeya Chat."

Why was my question “ Kiruv and outreach arguments” closed


Graph Editor - Active curve name?

Question: I often have tons of keyframes for tons of things in the scene. Sometimes I have a key selected in the graph editor but I just don't know which object this key belongs to. Any idea how to check the active key object name fast? Scrolling the object list on the left shows nothing, if there is any highlighted name I can never find it.
Answer: As generally we select the object we want to edit, and then operate, this seems a non-well implemented function.
This is the fastest way I've found:
Box select all the objects in the graph editor list, press numpad + three times (until every channel is expanded, press - to collapse).
Select the point you want to edit and press shift H to hide everything else (Alt H to unhide).
The corresponding channel will be the only one with the eye icon active.

Graph Editor - Active curve name?


Extending a discrete sub group to a lattice in unimodular Lie groups

Question: Given a unimodular Lie group $G$ and a discrete subgroup $\Gamma\subseteq G$, under what conditions does there exists a discrete subgroup $H$ s.t. $\Gamma\subseteq H$ and $G/H$ has finite volume? Also, can someone give an example of a discrete subgroup $\Gamma$ of a unimodular Lie Group which cannot be extended to a lattice?
Comment: If you take a discrete cyclic subgroup in $SL_3(\mathbf{R})$ generated by an element whose trace is transcendental, then it cannot be extended to a lattice since any lattice is arithmetic (Margulis) and hence trace of its elements are algebraic.
Answer: The same argument as in Yves' comment applies whenever you have a discrete subgroup of a semisimple Lie group without factors locally isomorphic to $SL(2,{\mathbb R})$, since Mostow Rigidity (or even local rigidity) suffices here (this observation is due to Selberg). The best result in the positive direction is due to Robert Brooks: If $\Gamma$ is a geometrically finite subgroup of $PO(3,1)$ then it admits arbitrarily small deformations $\Gamma_i$ (isomorphic to $\Gamma_i$) all of which are subgroups in lattices. In view of the later density theorem of Brock and Bromberg, one can replace geometric finiteness assumption here with merely "finitely generated".
In the case when $G=PO(2,1)$ then one can do the same without deformation, you just need to assume that $\Gamma$ is finitely generated (unlike Brooks' result, this observation is elementary: If $S$ is a finite area hyperbolic surface/orbifold with geodesic boundary, then the double of $S$ across the boundary is a finite area hyperbolic surface without boundary). However, if you allow infinitely generated discrete subgroups of $PO(2,1)$, then again there are counter-examples: It suffices to take infinite area hyperbolic surfaces with non-discrete length spectrum: They cannot cover finite area hyperbolic surfaces.
Also, if you are willing to re-embed $\Gamma$ in another Lie group, then it suffices to assume that $\Gamma$ is a subgroup of $G(O)$, where $G$ is an algebraic group (say, over the integers) and $O$ is the ring of integers of a number field $F$ (no need to assume discreteness here). Then $G(O)$ is a lattice in a (finite) direct product of Lie groups
$$
\prod_{\nu} G(F_\nu),
$$
where each $F_\nu$ is either ${\mathbb R}$ or ${\mathbb C}$ (this construction is called restriction of scalars). In the case of groups of rank $\ge 2$ this is essentially optimal by Margulis' arithmeticity theorem.
Comment: A quick follow up. When you re-embed $\Gamma$ into another Lie group, does the original group $G$ also embed into that group?
Comment: @Davis: The group of, say, real points $G({\mathbb R})$ does embed in the new Lie group $L$, but this embedding (in general) does not agree with the embedding of $\Gamma$ as a subgroup of a lattice in $L$.


Won't let me sign in with gmail

Question: When I deleted and re-downloaded the game, it won't let me sign in with my gmail account and it won't give me the option to, it only says sign in with Pokemon trainers club
Answer: You'll need to give it some time.
The Log-in options should disappear whenever the servers are offline due to issues or maintenance. Unfortunately, sometimes you'll have one but not the other log-in button appear even if it's not working for anyone.
The following 3rd-Party site has been pretty good in giving a glimpse if the servers are still down: http://www.mmoserverstatus.com/pokemon_go

Won't let me sign in with gmail


'Fifty pence', 'fifty pence piece' or 'fifty pence pieces'?

Question: May you tell me what is the difference among them? I see these three words in one paper and I feel these words are the same meaning.
Comment: Could you [edit] your post to include the source, and some sentences/paragraphs where you found these?
Answer: Well, "fifty pence" is an amount of money. "Pence" is another way of saying "pennies" when referring to the currency (but not to the actual coin itself).
A "piece", in this context, is a "coin". So "fifty pence piece" is a coin that is worth fifty pence.
"Fifty pence pieces" is just the plural of that. It means several coins, each of which is worth 50p.
Comment: You could say 'one pound piece' and be understood, in fact coin collectors use the term. So you could talk about "fifty pence and one pound pieces (or coins)".
Comment: But I see this phrase: fifty pence pieces and pound coins. If "fifty pence piece" are referred to "coin", how can he said: fifty pence pieces and pound coins? He obvious repeated.
Comment: What's the problem? He just chose to use different synonyms. That phrase means "coins that are each worth 50 pence and coins that are each worth one pound".
Comment: What he said can be transfer to: a coin that is worth fifty pence, and pound coins. Am I right? How could you know that what he said are coins that are each with 50 pence and coins that are worth one pound each?
Comment: The "coins" is referring to things that are worth one pound each, and it is plural. The "pieces" is referring to things that are worth 50p each, and it is plural. Those are separate things, but both are true.
Answer: In the particular example there is some idiomatic usage.
The silver-coloured, seven-sided coin that is worth 50p is called "a fifty pence piece"
The gold and silver coloured, twenty-sided coin that is worth £1 is called "a pound coin".
There doesn't seem to be a logical reason for this. But we tend to say "five/ten/twenty pence piece" but "(two) pound coin".  It is quite common to say "fifty pence coin", but "one pound piece" is rather unusual (perhaps limited to coin collector jargon)
So "fifty pence" is an amount of money, it could be a coin, or cheque or a number in a bank account. "fifty-pence piece" is one specfic coin (silver with seven sides) and fifty-pence pieces is the plural.
Note that "fifty" in these examples is the value of the coin, not the number of coins.

He has seven fifty-pence pieces, and five two-pound coins, so he has £13.50 in total.

If you meant 50 coins, each worth 1p you would say "50 pennies".  The name of the 1p coin is "a penny"

‘Fifty pence’, ‘fifty pence piece’ or ‘fifty pence pieces’?


WiFi connection only lets me access https, not http

Question: I'm having problem with my internet connection. I can't access the websites which I normally do. I get this error from Google chrome 'Connection to [website] was interrupted'. But the websites I access on https are working fine. Also, other laptops connected to wifi does not experience this problem.
I can't also access the router's setting page when I go to the router's ip address on the browser.
Answer: Double check that you don't have an HTTP proxy set.
The full navigation to those settings is a mouthful:

Go to the Chrome right side menu, and choose Settings.
Click on the "Show advanced settings" link.
Under the "Network" heading, click the "Change Proxy Settings" button. Windows' "Internet Properties" dialog will open to the Connections page.
Click on the "LAN settings" button.
Now you can uncheck the box in the "Proxy server" section if you don't need a proxy (or if you do, enter the correct details)
Comment: Had the same problem, for me it WAS the proxy settings!
Answer: It happens if you do not have correct date and time settings, Please reset you date and time settings. This will resolve the issue.
Comment: why would this be an issue?
Answer: I finally got it working thanks to a friend. It wasn't an issue on proxies, router setup, connection settings, etc. but it was because of my anti virus. For some reason, it's blocking my connection to the internet.
My antivirus is Avast free version by the way.
I disabled it and now everything is working fine.
Comment: The Trend Micro services had locked up for me. Killing them off allowed http access again. But Windows is now continually reporting the AV software is off, even though it provides a "link" to the Agent showing the status of "ON". A reboot is probably required :-(
Answer: It's not an issue to your PC or any end devices connected in WiFi .
Just go and search in your WiFi router.
Is there any management page? Inside that check local management. There are two check options, click both HTTP and HTTPS and save the settings. Reboot the router. Issue will be solved.
Comment: Welcome to Super User! Please read the question again carefully. Your answer does **not** answer the original question, which is not about accessing the router's management page using HTTP.


Where is the source code for Ethereum stored?

Question: I am interested to see exactly what is coded for Ethereum. I know web3 is on github. Where is all the fundamental source code stored for the EVM and all the main components?
Answer: The two most popular Ethereum clients are:
Go-ethereum (geth): https://github.com/ethereum/go-ethereum
and
Parity: https://github.com/paritytech/parity/
Here are some sections of the Geth client code that I have catalogued as useful for my purposes, which are mostly related to the EVM.

Determines which opcodes are valid in each epoch, and also has a 'read-only' mode for byzantium:
https://github.com/ethereum/go-ethereum/blob/master/core/vm/interpreter.go
Just objects with opcodes:
https://github.com/ethereum/go-ethereum/blob/master/core/vm/opcodes.go
Gas metering:
https://github.com/ethereum/go-ethereum/blob/master/core/vm/gas_table.go
Has implementations of the opcodes:
https://github.com/ethereum/go-ethereum/blob/master/core/vm/jump_table.go#L85
Brings it all together?
https://github.com/ethereum/go-ethereum/blob/master/core/vm/evm.go
Impls of precompiles: https://github.com/ethereum/go-ethereum/blob/master/core/vm/contracts.go


Does Canonical pay application developers?

Question: When an application becomes default in Ubuntu, does Canonical pay the developer(s) for making it default or do they just use the application for free?
Answer: All of the default applications in Ubuntu are free software, and in most cases, certainly in all cases that ship on the CD, that means they are not for sale.
If Canonical did pay, it would be a gift. They ship software under the same licenses the software itself ships with. So, in most cases

there just isn't any product or service that Canonical could pay for, even if they wanted.

However, Canonical and other Linux distributors do sponsor by employing developers to work on software, of course. And, like TheX says, they contribute to the software itself. Which is the whole point.
Comment: I don't think any of this follows. Canonical isn't Ubuntu, it's a company that finances and controlls Ubuntu. Canonical sells support, and software services. It's possible to sponsor software that you support, hire developers to develop it, and for that payment not to be a "gift" but mutually beneficial. They have hundreds of millions in revenue. They can certainly "pay" for products and services (many others companies do).
Answer: They "pay" by contributing any bug fixes, feature upgrades back to the developer, as consistent with the nature of open source software, not to mention the press that such applications get by being included as the default software of a major OS.
Answer: Open source software is determined by the license. There is nothing to stop a company from paying a software developer and then licensing their work as GPL for example. Clearly most open source developers aren't paid for their open source work.
Comment: This is not always the case.  The Linux Foundation published a report "**Who Writes Linux**" (http://www.linuxfoundation.org/sites/main/files/publications/whowriteslinux.pdf); in this the conclusion is that *"over 70% of all kernel development is demonstrably done by developers who are being paid for their work."*
Comment: Thanks for the clarification as it applies to kernel developers.
Comment: Here is an old study (2010) that mentions that 70% of code commits to Gnome are from paid developers.  https://www.redhat.com/de/blog/gnome-study-shows-red-hat-desktop-development-lead
Answer: Yes.
Canonical isn't Ubuntu; it's a multinational corporation that finances, owns, and controls Ubuntu. Canonical sells support, and software services. But, they have hundreds of millions in revenue, with offices around the globe. While it's true, the software in Ubuntu is largely not created by Canonical, it's not true to state that "Canonical does not pay developers".
For example, Canonical paid

Scott James Remnant to create Upstart
Alan Griffiths, Kevin DuBois, were either on contract or paid for the development on Mir.
Mathieu Trudel-Lapierre on Network Manager
Michael Hudson-Doyle developing Launchpad and Go.
Iain Lane cPython/Launchpad

I would guess there is a hundred? Other projects have been sponsored (GNU Bazaar), and other open source products like Quickly, juju, Storm, and Snap.
Also in 2017, 1% of the Linux Kernel Contribution comes from Canonical (that's not a high number at all, but it's non-zero).
Comment: Good answer 7 years after the question.


WH and Banshee interaction

Question: I was a Witch Hunter in mcw-001 and had marked the banshee as a witchcraft user before they were lynched. Later they possessed a body and the mark to kill showed on the possessed body. What happens when a Witch Hunter kills the body that has been possessed by a banshee they had previous marked?
Answer: This seems like a UI Inconsistency due to the ordering of events.
I believe what is occurring here is that the "marks shown to witchhunter" event occurs before the "banshee reverted back to the dead player" event.
You're seeing the mark because that's where the player you've marked (Remember that all abilities target the player not the identity) was at that time. However they immediately then swapped back into the grave after that event was sent.
If you were to then click on your night action button next to that identity you would actually be checking the real player who is in that identity (not the banshee) as they will have returned from the grave.

WH and Banshee interaction


ruby when to eigenclasses come into existence

Question: Do Eigenclasses exist prior to a singleton method being defined
on a Object or Class. ie Do they always exist or come in existence
when a singleton method or class method in defined?
Answer: Every object always has a singleton class. Period. No ifs, no buts, no exceptions.
Depending on how clever the compiler or interpreter is, it may or may not perform some performance optimizations. But like all performance optimizations, those are not allowed to change the result of the program, so even if those performance optimizations do lead to certain states where a particular singleton class does not actually exist, the program still must behave as if it did exist, so you wouldn't be able to tell anyway. After all, that's pretty much the definition of "performance optimization".
Some Ruby implementations may do some optimizations, others may do other optimizations, some may even not do any optimizations at all. You can't tell from the result of your program, and you shouldn't care, you mustn't care.
For example, YARV performs the following optimizations:

Since almost no object has singleton methods, creating a singleton class for every object would be a waste of memory, therefore singleton classes are created lazily: when you create a singleton method (def foo.bar or Object#define_singleton_method), when you open up the singleton class (class << foo), and when you ask for an object's singleton class (Object#singleton_class).
Since almost every class has some sort of class method, the overhead of lazily creating a singleton class doesn't make sense, so for classes, the singleton class is always created eagerly.

But this is a private internal implementation detail of YARV. JRuby may do it differently. IronRuby may do it differently. MacRuby may do it differently. MRuby may do it differently. Topaz may do it differently. Rubinius may do it differently. MagLev may do it differently. Even the next patchlevel of YARV may do it differently.
If you look at the singleton class it's there. If you don't look at it, it doesn't matter whether it's there. So, semantically, it's always there.
Answer: for objects like class, when a new class is created its eigenclass is also created, and of their object when they are created.
example:- creating a class
class User; end

or
User = Class.new

its eigenclass is also created at the same time,
and there a separate eigenclass is created for every object of User class


What is electric dipole?

Question: I don't understand the electric dipole as it is described in my physics book.  According to what I have read in my chemistry book, I know that the dipole is the gain of partially negative charge in the electronegative end and vice versa.  This results in a type of weak Van der Waal force.  However, in physics I don't find the same explanation.  In physics, it is described as the product of the magnitude of charge, $q$, and distance between the two equal and opposite charges, $\textbf{d}$. How can both of these definitions be the same?
Answer: The dipole moment is uniquely defined as
$$\vec{\mu}=\sum_i^N q_i \vec{r}_i$$
Unfortunately in Chemistry, when the molecular dipole moment is represented, that is done as an arrow with a cross in the tail pointing from the positive charges to the negative ones.
The reason why this convention is so common in Chemistry is because it reflects atomic electronegativities: for example the oxygen being more electronegative than hydrogens "pulls" electrons towards itself, leading to the partial charges represented with $\delta^{+}$ and $\delta^{-}$.
On the other hand the formal definition of a dipole moment (the one given above) is represented by the following vector representation

To sum up the dipole moment is a vector uniquely defined that contains information about the charge separation. However in Chemistry it can be represented in the opposite way (only represented: when we (chemists) do calculations we of course use the formal definition).
In practice the molecular dipole moment is obtained integrating the electron density since we have a charge distribution all over the space and not fixed partial charges, thus it is an expectation value of the molecular wavefunction. There is no need to invoke Van der Waals interactions for defining the dipole moment!
I really hope it helps! :)
Answer: I'm not very familiar with the chemical term, but they do sound like they are the same.
An electric dipole is an object (or, in general, a charge distribution), where the two charges are not evenly distributed. Imagine a convenient object for starts, like a rod. The positive and negative charges could be completely separated spatially, or they could be mixed but unevenly. You have an electric dipole in both cases, and its moment is stronger in the first case. (You can see that it is stronger from, as you said, the product of the magnitude of charge and distance.)
"The gain of partially negative charge in the electronegative end and vice versa" sounds like such a case. The van der Waals would be a result of this configuration.

What is electric dipole?


Successful password resets and suspicious scripts on my Wordpress instance

Question: On 2 Wordpress instances that I'm hosting, I've seen several password reset requests on 3 different accounts in the last days, some of which were successful, even though I am sure that the reset link in the e-mail was not clicked. Since the e-mail addresses are hosted at different providers, I think it is unlikely that the e-mail account itself or its provider is breached. The password reset requests were triggered by IP addresses registered in Russia and Turkey (126.96.36.199, 220.127.116.11, 188.8.131.52, 2a03:afc0:9::9).
One one of my instances, 2 of the breached user accounts are administrators. On that instance, I have made the following observations:

An Application Password was created for each of the users.
Some suspicious PHP files containing obfuscated code have appeared in the wp-content folder (wp-content/options.php, wp-content/2020/xzmpocbt.php, wp-content/2024/swryjqcg.php). All 3 have an mtime of 2022-01-28T23:33:19, but they don't appear in the backup from 2 days ago, so it seems like they were created during the attack. Virus scanners seem to flag the files as HEUR:Backdoor.PHP.WebShell.gen.

On the other instance, the breached user account is not an admin, and I have not detected anything suspicious there yet. However, I don't have much logging in place and I'm not sure if Wordpress has anything like an audit log, so I'm not even sure where to look for suspicious changes.
Both Wordpress instances are running the official Docker image and have been last updated a few weeks ago. Other Wordpress instances that I'm hosting in the same way don't seem to be affected.
Both instances have a variety of active plugins. The ones that both have in common are:

Advanced Editor Tools
Classic Editor
Contact Form 7
HumanCaptcha by Outerbridge
iframe
Post SMTP
Simple Lightbox

To mitigate the issue, I have deleted the application passwords, reset the passwords of the affected user accounts, deleted the suspicious files, pulled the latest docker image, recreated the docker container and reinstalled all plugins.
My questions are:

Are there any known recent security vulnerabilities in Wordpress itself or some of my plugins that could have caused this?
Do you have any more tips how I could look for suspicious changes and how I could revert the possible damage caused by the attack?
Answer: This is a bug in the POST SMTP plugin. It has been reported here, and also the plugin support forum is full of reports of the same issue.
The issue has been fixed in version 2.8.8 of POST SMTP.


Why do we need a two-Higgs doublet model and why only one extra doublet is added to the extension?

Question: The general two higgs doublet model can neither give masses to neutrinos without considering a see-saw mechanism nor it can unify gravity with other three forces. To explain dark matter also we have to introduce extra symmetry to the theory. Then why do we need this theory?
Comment: What do you mean by "need"? If you mean how it is motivated, one motivation is that supersymmetric versions of the standard model come with at least two doublets. E.g. when you remove all superpartners from the MSSM you have a 2-Higgs doublet model.
Comment: Thank you.. My question is what we can do using this model?
Answer: The main motivations are (see e.g., 1106.0034):

Two Higgs doublets are required in supersymmetric models as the superpotential must be holomorphic and to avoid triangle anomalies (see e.g., 9709356).
Two Higgs doublets could introduce extra sources of CP-violation, an ingredient for baryogenesis (see Sahkarov's conditions). The CP-violation could be explicit or in fact spontaneous in some more exotic models.
Two Higgs doublets could have a richer vacuum structure, with more chances for a strongly first-order phase transition. Such a transition could provide a departure from equilibrium, another ingredient for baryogenesis.
It is a simple extension of the SM that doesn't shift the the $\rho$-parameter.


Why does each plate receive a charge exactly the same magnitude in parallel plate capacitor?

Question: When a parallel plate capacitor is connected through a cell, each plate of the capacitor receives a charge with the same magnitude, but with the opposite sign. Is it because of the battery or the area of the plates?
Comment: Conservation of electric charge ,if charges on one plate decreases , charges on the other plate must increase by equal amount.
Answer: Suppose you have a simple circuit with a capacitor and a power supply:

You want to create a charge on the capacitor, so you turn on the PSU to add some extra electrons to the upper plate:

But the number of electrons in your circuit is constant. The power supply can't create or destroy electrons. All it can do is act like a pump to move electrons round the circuit. Specifically it can pump electrons from the bottom plate round the circuit to the top plate:

So for every electron that you add to the top plate you have to remove an electron from the bottom plate, and that means the negative charge on the top plate is necessarily always equal to the positive charge on the bottom plate.
Comment: Sorry for reviving this but I had the same question. I have a question about your answer though. I suppose not PSU's are the same, but I'm thinking about a battery -- perhaps your answer is influenced by that. Don't the electrons on the bottom plate naturally want to go towards the battery since that's the anode? In other words, its not the push of the electron going towards the top plate, its the pull of the protons on the anode.
Comment: @TypicalHighschooler I deliberately left it vague as to what exactly the PSU is because it doesn't make any difference. In the case of a battery a chemical reaction inside the battery consumes electrons on one side and emits electrons on the other so one side has a net negative charge and the other a net positive charge. The electrons in the circuit are simultaneously pushed away by the negative charge on the anode and pulled towards the positive charge on the cathode.
Comment: So then my question is this: aren't the electrons in the bottom plate naturally attracted to the cathode since there is positive charge there? For example, consider a case where you only connect the bottom plate to the cathode; you don't connect the top plate to the anode. Then the electrons in the bottom plate and the wire will spread out since there is the positive terminal of the battery attracting them. In this case, after you connect the top plate to the anode, there won't be equal charge on both plates.
Answer: The battery creates a potential difference between its terminals. Because, in a steady state situation, the total voltage through a closed circuit is zero, this will create, when the capacitor is charged, the same voltage over this component.
Then, if the charges on the capacitor plates wouldn't be equal in magnitude (!), the electric field outside (and inside as well) the capacitor would not be zero. However, in steady state the electric field inside a (perfect) conductor, the wires in this case, is always zero.


What is the site's policy on slang words?

Question: Here in this question, a new user answered but used the 4 lettered word starting with a 'd' to refer to the male generative organ, which is considered as a slang. I thought of editing the answer to remove the offensive 4-lettered word, but then I thought that it would create a bad precedent (of others covering up application of expletives with the OP bearing no consequences whatsoever) & didn't actually solve the real problem about the usage of expletives. Besides, apart from using the expletive word, the answer was fine in other categories. Currently, no feature exists to flag answers using cuss words. I have seen many people incorporating slang terms into their daily vocabulary & the user may be one of those sort of people, but that can't be considered a valid reason to report somebody. So I would like to what should be done in such cases where slang terms are casually incorporated into answers.
Comment: *..Currently, no feature exists to flag answers using cuss words.* <-- You could use custom mod flag. The answer is full of swear words which we don't entertain. but since they are a new user, as old users, we can help such users by pointing out what they need to improve. But if this goes on; as in said user doesn't stop, feel free to make a custom flag to mod.
Answer: Per the Meta FAQ,

Since the community has awarded you with enough reputation points to edit posts, the community trusts you to do the right thing when you see offensive posts: You should trust your own judgment too, and do what you feel is necessary in the particular situation.

My own opinion is that we should edit these out; Hinduism.SE and the Stack Exchange network as a whole are supposed to be academic. That means that language should be fairly formal and we shouldn't really have any slang, whether it's vulgar or not.
Even though 'dude' isn't an offensive word, it's still a bit out of place on our site, and future visitors would likely prefer the second option here:

then shiva told the other dude that he oughta kill the elephant.
Then, Lord Shiva told the other man to kill the elphant.

So I think the same idea applies in an example more similar to the one you bring up, where the slang word is actually vulgar:

In the shiva purana, lord shiva touches his d*ck

There is one scene in the Shiva Purana where Lord Shiva touches his penis/reproductive organ.

Again, the second answer is more clinical and academic, and therefore probably better.

I would say that you should edit it out, but the answer itself is kind of poor and reads more like a rant that happens to quote a few scriptures.
You could always flag it for mod attention if you're really unsure.


Topics in Combinatorial Group Theory (for a short talk).

Question: I have started course on combinatorial group theory and supposed to give a short talk/presentation. It would be really helpful if someone can suggest some good/interesting topics to cover.
Thanks
Comment: Talk to your professor?
Comment: @MichaelJoyce that can be done but i was looking for out of box suggestion that may interest anyone, i hope you understand
Answer: Combinatorial group theory is a large subject, and is somewhat ill-defined (it is thus called because it uses combinatorics heavily, or because it utilises a combination of techniques? I have heard both argued...). For the purposes of this answer, I shall take it to mean "the study of abstract, discrete infinite groups and their presentations". By discrete, I simply mean we are not considering any topology on the groups. Since the 1980s the more trendy subject of "geometric group theory" has been leading the way, but these subjects are broadly similar and the symmetric difference of the practitioners is very small (by my own observations - please feel free to disagree!).
Dislaimer: I should say that I cite quite a few of my own posts in this post. That is because I am talking about stuff I find interesting so have posted quite a lot of stuff on Math.SE on this!
When working on a talk it is often useful to know the history of the subject you are working on. I stumbled across a wonderful article on the pre-70s history of combinatorial group theory (and really pre-70 is what you are after!) called Some groups I have known by B.H.Neumann. (It is worth pointing out that the "Hanna" he makes reference to is his late wife. Both B.H. and Hanna were formidable group theorists (they are the N and N in HNN-extensions), and two of their sons, Walter and Peter Neumann, have justifiably similar reputations.)

Some Classical problems you may find interesting

Broadly speaking, there were four questions which drove combinatorial group theory in the early days. The first is called Burnside's problem, the last three are Dehn's problems (the word, conjugacy and isomorphism problems).
The Burnside problem A group is called torsion if every element has finite order. Burnside's problem asks if it is possible for a finitely generated infinite torsion group to exist. Note that without the "finitely generated" the question has an obvious answer: just take the direct sum of infinitely many finite groups. The wikipedia article is pretty good on this, and I am not sure that I have anything to add. I would like to point out that 1) a fields medal has been awarded for work on the modified version of this problem 2) the current prize for "best example" goes to Ol'shanskii, and 3) Novikov and Adian (pronounced "Adyyyyyyaaan") play important roles in the story of both this problem and Dehn's problems. Finally, all known examples are infinitely presented. Find a finitely presented infinite torsion group and people will know your name...
Dehn's problems I wrote a long post on Dehn's problems here.

Some topics which I would speak on if I was in your place

If I wanted to give a talk on combinatorial group theory, but didn't just want to point out that free groups have soluble word problem (say what now?!?), I would give an introduction to one of the following areas. But I am not you. These are just some ideas for you to ponder...
Non-Hopfian groups A group is Hopfian if every surjective endomorphism is an isomorphism, so a non-Hopfian group is a group which has a surjective endomorphism which has a non-trivial kernel. For example, consider the infinite (countable) free group and then kill a generator. The resulting group is still infinite (countable) free, so this group is non-Hopfian. A more subtle example is the so-called Baumslag-Solitar group $BS(2, 3)=\langle a, b; b^{-1}a^2b=a^3\rangle$. I wrote a lengthy post on these groups here, and an excellent, and very old, article which talks about their early history is A two-generator group isomorphic to a proper factor group by B.H.Neumann (this is pre-Baumslag-Solitar's example).
van Kampen diagrams van Kampen diagrams give a way of visualising the word problem. If all diagrams satisfy certain conditions (called the small cancellation conditions) then your group has soluble word and (if the conditions are strong enough) conjugacy problem. The classical reference is the last chapter of Lyndon and Schupp's book Combinatorial group theory. See also this post of mine.
Fundamental groups of graphs The fundamental group of a graph is a free group. If you are comfortable with covering spaces and so other stuff from topology then you can prove some remarkable results about free groups by thinking of them as fundamental groups of graphs. You would want to look up something called "Stallings' foldings". The original paper is The topology of finite graphs by J.Stallings, and you will also find Allan Hatcher's book Algebraic Topology helpful. See also this post of HJRW.
Bass-Serre theory Bass-Serre theory is the theory of groups acting on trees. HNN-extensions and free products with amalgamations all act on trees, and if you have ever heard of a "graph of groups" then it is an object from this theory. Bass-Serre theory is extremely powerful, and a wonderful introduction to group actions. The classical text is the book Trees by Serre, although there is a modern book called Groups, graphs and trees by John Meier which is much more readable.
One-relator groups A one-relator group is a group with a presentation of the form $G=\langle X; R^n\rangle$, $n\geq 1$ and $R$ not a proper power of any element. It has torsion if and only if $n>1$, has soluble word problem, every torsion element is conjugate to a power of $R$, and if it is freely indecomposable then every proper subset of $X$ generates a free group. All of these wonderful results can be proven using a standard method, called Magnus' method. The idea is to induct on the length of the word $R^n$. If you have Magnus, Karrass and Solitar's book then the proofs are tricky, employing groups with "staggered" presentations. A chap called Moldovanskii realised that you could use the same idea, but instead embed $G$ into an HNN-extension of a group with a shorter defining relation (this is substantially neater). The best references I have found are an article of Fine and Rosenberger The Freiheitssatz and its extensions in a book called The mathematical legacy of Wilhelm Magnus, and a paper of McCool and Schupp On one-relator groups and HNN-extensions.
The word problem for the fundamental groups of closed, orientable surfaces When Dehn posed his three fundamental problems of group theory he proves that the fundamental groups of closed, orientable surfaces of genus at least two have word problem soluble by "Dehn's algorithm" (not that he called it that, mind!). His proof led to the development of small cancellation theory (mentioned in the "van Kampen diagram" paragraph, above) and ultimately to the development of hyperbolic groups and all that they lead to (I talk more about this in my post on Dehn's problems which I mentioned nearer the top). Because of this pedigree, it would be interesting to go through these proofs and see if you could present them in your talk. I do not know if this is possible, but certainly if I was going to do a talk next week this would be my subject of choice: explain Dehn's original proof! (Or give a modern proof of it. Or something.)
Anyway, I hope you found this all useful. You really should speak to your professor about this, but also you want to think about it by yourself. You want to find something which you find interesting, not just something your professor thinks is "at about your level..."!
Comment: really thanks, this gives me things to work out.
Answer: I would add to the list some of the problems from identities among relations. (A good article to consult is
J.-L. Loday, 2000, Homotopical Syzygies, in Une dégustation topologique: Homotopy theory in the Swiss Alps, volume 265 of Contemporary Mathematics, 99 – 127, AMS.
The visual element is good so it makes for a nice presentation. The idea is very simple but then its development requires a bit of care, so again a nice topic to handle. The subtopic of Pictures is also neat.
Comment: It should be pointed out that pictures are dual to van Kampen diagrams (I think Pride came up with them first, and I think actually that these pictures are slightly different from Pride's ones. Hmm...). And I agree that they are very neat!
Comment: Igusa is credited with them as well and may have the edge on Steve Pride. My main point is that that material is a very nice intro to some of the outward looking links from Comb. Group Theory. It is fun, and easy to present as it does not require that much background.
Comment: Ah, okay, I had never heard of Igusa before, but know something of pictures. I'll look his stuff up. You live and learn :-)
Comment: Loday's paper is a good one to get those aspects of pictures and has the references to Igusa.
Answer: How about the Banach-Tarski paradox? (Assuming you are not already covering it in your course. ). Google will give you some nice links.
Comment: I don't how to relate Banach-Tariski paradox with combinatorial group theory. I understand its strong relation with axiom of choice but how it would help here?
Comment: The free group of rank $2$ acts on the sphere by orthogonal transformations.  By carefully dissecting the free group, you can produce paradoxical decompositions.  The Wikipedia article explains it all very nicely.  Of course, as was already suggested, your instructor can indicate whether the topic is actually suitable for your course.
Comment: Thanks James, I'll see what he says. Otherwise I am thinking of presenting some remarkable theorems regarding free groups.
Answer: What about automatic,autosimilar groups..the word problem and all that stuff..for example
http://en.wikipedia.org/wiki/Grigorchuk_group
Comment: It sound interesting. Thanks


Should I get a SATA 3Gb/s or 6Gb/s hard drive for my MBP?

Question: If I am planning to upgrade my Macbook Pro 13" (Late 2011) with a 7200RPM Hard drive, should I get a SATA 3Gb/s or SATA 6Gb/s drive?
Answer: As a conventional hard drive wouldn't come close to 3GB/s, I say save some money and go for the cheaper 3GB/s one. If you have money to splash then instead I suggest you go for a SSD, because that would really lift your MBP's performance. It doesn't have to be as large and your current drive, because you can use your current drive as a external one by getting a SATA to USB casing somewhere to take some of the load off.
Answer: Short answer: it doesn't matter.
Longer version: Either will work fine. SATA is backwards compatible, so SATA 6Gb/s drives will work on SATA 3Gb/s interfaces and vice-versa. The 2011 Macbook Pros have 6Gb/s ports for the HD (some in the optical bay as well). However, no mechanical hard drive can come close to maxing out SATA 3Gb/s speed, so you'll see no difference from a 6Gb/s drive or interface. It makes a difference with SSDs, but with hard drives, it's merely marketing.
Comment: Yea it looks like 7200RPM drives max out at about 1gbps...
Comment: Yes, that's about right. Some of the newest and highest capacity drives can hit a bit north of 150 MB/s, which is still below the 1.5Gb/s theoretical limit (192 MB/s).
Answer: Another option, if you don't really need the optical drive is to get an adapter and put a  big conventional drive in the optical bay (via an adapter such as from OWC) and then put a 6Gb/s SSD drive in as your boot drive. Super fast, and very useful. I'm finding optical drives to be less important than they used to be unless you're a gamer.
Comment: Yea I have seen the OWC conversions.  What I'm weighing is the awesome performance of the SSD in my MacBook Air 11 vs. having a ton of space with say a 750gig 7500rpm in a Pro.


Number of vowel heights in European languages

Question: Is there any language with a vowel system that cannot be analyzed as having no more than three degrees of height with the addition of some other feature (length, tenseness etc)?
Comment: Danish contrasts long and short vowels, but not (according to most) tense and lax. Some vowels are of course tenser than others, but tense/lax is not usually said to be phonologically distinctive in Danish. The four vowels I cited in the example above are all long (and tense), and I'm not aware of any analysis that manages to reduce them to only three vowel heights.
Comment: Your title specifies European languages; the question just asks about "any language" – are you specifically looking for European languages only? Such languages do exist within Europe (e.g., Danish has minimal groups such as _mile_, _mele_, _mæle_, _male_ that show four vowel heights), but including languages from elsewhere would significantly increase their number.
Comment: Sorry, this was a brain fart - yes, I was asking about European languages specifically; and "European" in a broad geographic and political sense, not linguistic. OTOH note that it's not about vowel height alone, but about how much is necessary to clearly identify phonemes *when considering other contrasting features*.
Answer: You describe the standard possibilities given the SPE features [high], [low], [tense]. Bearing in mind that [+hi,+low] describes a physical contradiction so is not expected to exist, that allows three combinations, each of which can be combined with [+tense] or [-tense], admitting as many as 6 formal distinctions. English has 5 of them: [i ɪ e ɛ æ] and some dialects have two front unrounded vowels [a ae]. The crucial distinction in your question (which was the question raised in feature theory) seems to first exclude tense / lax from the domain of "vowel height". So is [tense] (alternatively [ATR]) a vowel height feature, or is it something else? On what basis could we decide?
One (theoretical, but practically unworkable) approach is to try to answer based on physical production. The idea is to identify a physical correlate of "vowel height", either (horizontal) tongue position on some coordinate system, or (first) formant frequency, and ask if any language has more than three consistent physical clusters. The easy answer is "Yes, way more than three". Once you add in "controlling all other factors" (vertical tongue movement, F2 value), then the answer becomes "not even three". The IPA vowel trapezoid embodies this fact at least for front vowels. There has been a long-standing search for a purely physical classification of vowels, which simply has not panned out. The groupings do not leap out from physical measurements, instead, grouping may be surmised from analysis of the phonology of a language, and post hoc one may look for phonetic correlates of those phonological groupings.
The implied separation of "vowel height" from some orthogonal feature like "tense" presumes that certain features "act together" in a way that significantly excludes another feature. This makes no sense in the SPE view of feature organization, but is embodied in hierarchical theories of features via the notion of feature constituency – that there is a node "vowel height" which contains some specific features (hi, low), and that an orthogonal feature ("tense" or "ATR") outside of that constituent. In that framework ("feature geometry") you question then is potentially answerable. The question is: does any language have more than three phonologically contrastive arrangements of features under the Vowel Height node. We can answer the "under the Vowel Height node" using classic constituency arguments.
Constituency arguments are classically used to argue that in some languages like Akan or Kalenjin, the distinction [i e] vs [ɪ ɛ] is governed by a feature ATR which is outside of the Vowel Height constituent. The argument is based on the vowel harmony rule, where /ɪ ɛ ʊ ɔ/ become [i e u o] when an adjacent syllable contains /i e u o/. The situation where /ɪ ʊ/ become [i u] next to /i u/ doesn't tell you anything, because it can either be seen as complete assimilation of vowel height, or as partial assimilation of ATR. The compelling argument for ATR is the fact that /ɪ ʊ/ become [i u] (becoming physically higher) next to /e o/, which are physically lower.
This is the classic argument that ATR is not a vowel height feature. Well, what's sauce for the goose is sauce for the gander. Now we can turn to languages like Matumbi and Gbe which have multi-feature height assimilation, where for example /ɪ/ becomes [i] next to [i,u], [ɪ] next to /ɪ ʊ/ and [ɛ] next to /ɛ ɔ/; or /ɛ/ becomes [e] next to /e o/ and [i] next to [i u]. There are also languages where [i ɪ] or [e ɛ] is phonologically a vowel height distinction.
Parkinson (1996) undertakes an extensive survey of vowel height distinctions in phonology, ultimately arguing (analogous to one proposed by Nick Clements) for a theory using a single recursive feature, thus allowing in principle any number of vowel heights to be represented. The most compelling case for multiple vowel heights comes from Sesotho, which is claimed to have up to six vowel heights (one of which exists only as the result of an allophonic rule, and one of which is limited to the vowel [a] which is the sole vowel where backness and roundness are not correlated). The argument for the height hierarchy [i ɪ e ɛ] is based on the vowel harmony pattern, which can be stated as "a vowel (other than /a/) raises one degree when followed by a higher vowel", thus /ɛ/ → [e] before /i, ɪ/, but /ɪ/ only raises before /i/, and not /e/ (which it does under the ATR pattern of Akan). Since /ɪ/ both triggers raising and undergoes it, an ATR analysis is not viable.
In other words, Sotho is the base case argument for more than 3 phonological heights.
Comment: In the sense of "being able to represent phonemic distinctions". Sotho is a significant problem in terms of being able to formalize the rule, since no feature corresponds to "one step higher".
Comment: I should have mentioned that the question arose as I was reading Clements' "Hierarchical representation of vowel height", where he points out that e.g. French was successfully analyzed using three heights and tenseness; but then lays out the argument that "tense" doesn't clearly correspond to height, while the distinction is equally clearly about height, and so this is not a satisfactory analysis. Which is clear, but I got curious - if we ignore this argument about tenseness, and just accept it as a convenient fiction, is it sufficient (for contrast) at least for European languages?
Comment: So I guess the question could be rephrased as: are the 6 degrees effectively provided by the model with [±high] [±low] [±tense] sufficient?


Cufon font replacement: How can I eliminate the flash of unstyled text that occurs when the page loads?

Question: I'm using Cufon to replace the font of selected heading elements on a site I'm working on, but whenever I load a page, there is a noticeable flash of unstyled text before Cufon replaces the text. I expect that I may be doing it wrong. Here's what I have in the :

And here's what I have at the end of my document:

What am I doing wrong? Thanks in advance!
Answer: The browser renders the entire page (using the standard text rendering specified in your stylesheet), then the Cufon script goes back and replaces it. Due to the way browsers render pages, and the fact that the script fires after the page's DOMLoaded event, there's no good way to avoid the momentary flash of unreplaced text.
I said no "good" way... there are bad ways to do it, like hiding the text that's going to be replaced with CSS in your main stylesheet, but that's very bad for accessibility and/or people who have scripts/flash turned off.
Currently this problem is one of the known limitations of any script/flash-based text replacement techniques.
EDIT:
The 24 ways blog had an article on using Data URIs with the CSS3 @font-face declaration to avoid the "Flash Of Unstyled Text". Basically, you embed the font data directly into the stylesheet.
While it's not pretty, it does mean the font is loaded with the CSS and is ready for use immediately. @font-face is currently supported by Safari and Firefox, and will be supported in Chrome 4 (which is getting close). IE support is limited to Microsoft's EOT format, so I count it as "not supported".
Check it out: How to use Data URIs to avoid the Flash Of Unstyled Text
Comment: > Currently this problem is one of the known limitations of any script/flash-based text replacement techniques.

Thanks, Gabriel! I thought that might be the case, but I appreciate the confirmation.
Answer: Thought i'd add this for the next person who's looking for an answer to this issue
as it appears to have completely solved the issue for me.
.cufon-loading { visibility: hidden; }

The above CSS will hide the plain-text that cufon is replacing before cufon loads.
Answer: Hiding the headings using CSS visibility is not advisable for reasons mentioned above. IE8 also has a problem rendering the cufon text when it's hidden...
The alternative is to simply move the heading text off to the left of the screen while it's rendered, using a large negative 'text-indent' value.

You need to move the headings off screen using either standard CSS within the header, or if you are worried about hiding text from people who don't have JS enabled, the CSS could be set using jquery.
eg. '#id { text-indent: -9999px; }'

Then place your cufon replacement code just before the end body tag, within a set of script tags

Add a call to Cufon.now();

Using the jquery .css() method, bring the headings back into view by setting a text-indent of 0
eg. $('#id').css('text-indent', '0');

EDIT:
It seems the initial negative indent, must be set with CSS (rather than jquery) because the page needs to be fully loaded before the jquery code is called.
The danger in setting the indent via CSS, is that people who have JS turned off, won't get to see the headings at all.
If I find a reasonable solution, I'll post it here.
Answer: You could use js to insert a style rule to hide the cufon'd text before the body loads...

   ...

    ...


How to design Business Process Layer

Question: Well, I have some business process such as, creating Appointment List(non-persisted, will be persist later) based on some Configuration. I've service layer, which is transactional, but for reason, I don't need transaction for this task. Where should I place my code? How I separate my business service code from transactional service(working with Dao)?
Answer: There is no correct answer to this.
If you put all this code into your DAO, the DAOs will become huge.
If you put code like this into factories, you will get many, many factories and code working with this type of object will be in several places and developers will spend more time searching for something.
In both cases, you risk code duplication because someone will eventually need functionality that is already there but it's lost in the man methods of the DAO or the many factories/helper classes.

How to design Business Process Layer


When and where was WIMP dark matter formed?

Question: Is the formation of WIMP dark matter confined to the high number densities associated with the early stages of the formation of the universe or are conditions in the collisions of black holes such that it is still being formed?
Comment: WIMP abundance is set by a freezeout from thermal equilibrium. I don't understand your questions.
Comment: I was interested in whether the production of WIMPs continued in the later stages of the universe.
Answer: Essentially yes, the formation of WIMPs is confined to the early Universe. WIMPs can only form when the temperature is around the scale of their rest mass, and where the density is very large. In the early Universe these conditions were met, however now there are unlikely to be environments with such high temperatures and densities.
When a star collapses and goes supernova the matter is very dense and the temperature is around 10 MeV, so in principle new dark matter particles could be produced there, but not WIMPs which traditionally have masses above a few GeV. Even this only lasts a few seconds though, so the number of new dark particles produced in the supernova is small compared to the number which would have been produced in the early Universe.
Comment: Welcome to phys SE, i recognize your name from a few papers on neutrino/particle physics!
Comment: For completeness, formation of WIMPs also possible in colliders


Space elevator counterweight station keeping

Question: I working on a story, and there is a space elevator. I know that moon and sun have a gravitational effect on bodies in orbit. And if a heavy asteroid was used for counterweight, wouldn't it require a massive amount of propellant (or power depending on propulsion) to keep the north-south station keeping? Anyway, what I want to ask is if anyone knows how much influence would moon and sun be on the counterweight. Same, more or less or than on a large unanchored station in geostationary orbit.
Comment: Welcome to Worldbuilding!  Please be sure to take the [tour] and read through the [FAQ].  This is a good first question, IMO, and I need to think about an answer.
Comment: Fundamentally, this seems like an ordinary physics question, but not enough of the question has been described clearly to start filling in enough variables to make it answerable.
Comment: About the same as to station, because counterweight is pretty close to the geostationary orbit, and gravity acceleration does not depend on the recipient mass, while it's way less than the other body's. Here you speak about asteroid as counterweight, they still have way less mass than Moon or Earth or Sun, so count them as "big stations on the same orbit"
Answer: I don't have the math or orbital mechanics to prove it (despite playing hundreds or hours of Kerbal Space Program), but I'm inclined to think that if your ground anchor is smack on the equator, in one of the ground locations corresponding to the most stable points in GEO (the reason Taprobane -- essentially a fictional Sri Lanka but on the equator -- was chosen in Fountains of Paradise), station keeping for the counterweight could be nearly zero.
First, a geostationary satellite over one of these stable locations needs almost none to begin with, because these locations are potential wells in the geosynchronous environment -- and secondly, the counterweight is, in terms of forces, hanging from the ground anchor.  Any perturbation by the Moon or Sun, forward, backward, north or south, will create a restoring force that wants to return the tether to a vertical position.  This will, of course, result in some pendulum effect, but it should be possible to damp this (especially in the fore-and-aft plane) by timing transits of mass up and down the tether (momentum to bring those to orbital velocity is also supplied by the ground anchor through the tether).
In the end, I would suppose that having the ability to actually build a Beanstalk tends to presuppose the ability to stabilize it.
Comment: If the 'weight' of the station is 'hanging' from the planet, you have done something very, *very* wrong.  The counterweight station needs enough mass out beyond the geosynchronous point to counter the mass of the cable from the geosynchronous point to the ground.   The beanstalk is being held up by the counterweight.   The counterweight is **not** being held in place by the connection to the ground.
Comment: @MichaelRichardson, you want to keep the cable under tension, which means your counterweight isn't *quite* a perfect balance for the rest of the system.
Comment: Siri Lanka was moved for *Fountains of Paradise*. It isn't actually on the equator.
Comment: @JohnDallman It's been quite some time since I read that, but wasn't the terminus in a fictional country that if you squinted, kinda looked like Sri Lanka, but wasn't?
Comment: Yep, Taprobane (says a quick search).  I haven't read it since the year it came out, either.  Clarke called it "90% congruent with Sri Lanka" but further south.
Comment: Not to quibble, but technically he's saying that it is being *held down* rather than *held up*.