Distance of a people in an image

Question: What is the best approach to find the distance of a person/people from camera, using an image?
Comment: Welcome to DS StackExchange. Please make your question more elaborate. Explain for example what sources you found up to now, what did you try, if you have data avilable, etc. As of now it's too general.
Answer: Updated: Measuring distance from camera to object
Perhaps you could search and find tons of materials. This is a well-established task, for example this tutorial, of more advanced methods combining object detection with distance measurements, see Object-Detection-and-Distance-Measurement, and references at the bottom. In a nutshell, when you know details about your camera focal length and the details about the object in the image, it is a simple formula to estimate the distance base on those details. I am guessing that you may need to do some calibration, but I haven't done this one myself, so I wouldn't know for sure.

Earlier I have had: Measuring distance between objects
One idea that might be worth exploring is to segment your image, for example use the recent package by Facebook Detectron2, that seems to be capable of segmenting people out-of-the-box. Once segmented (filtered only for humans), for each segmentation calculate the center of segment (Centroid) or something similar assigned to each person. And given that would be (x,y) coordinate, you can easily calculate distance from a person to all neighboring people.
For the center of segment , OpenCV is quite handy. See this post Find the Center of a Blob (Centroid)! Or this great tutorial to estimate distance between objects in an image with OpenCV!
In a nutshell: Image Segmentation -> Centroid -> Distance
Comment: I see your point. But it doesn't mean you cannot do nothing. Take one person of an average size person (honestly the aspect ratio of people doesn't change that much) at fixed position and calibrate the distance. It seems like a viable option in practice like distance of cars from another car (again cars in various size and shapes). Unless I am missing something.
Comment: Thanks for the answer. But looks like this gives the distance between people, but I'm looking for finding the distance from a person to camera. Any thought on that
Comment: Oh I misunderstood you then. That is even more straightforward then. Have you searched online? I will update the answer momentarily.
Comment: I searched, what is needed for distance calculation are
* Actual dimension of the object, like width or height. (We might not have it)
* Focal length of the camera. (Which we can assume that we will know)
Comment: Makes sense. We also thought to train the faces to predict the actual width of the face :-)

Distance of a people in an image


Routing Engine / data for hiking trails (Austria)

Question: I currently use OSRM for the routing in my apps. This works well for car/truck routing. However, I have an upcoming project that requires routing on hiking trails as well. Are there any available solutions? If not, would it be feasible to use osrm and add the trails manually to osm? any other suggestions?
Answer: You can use OSRM for this purpose but you will require a hiking profile. The OSRM demo instance has just a car profile and won't do foot routing. However that's a limitation of this particular OSRM instance and not of the underlying OSM data.
Alternatively just use a different online router. There are lots of different OSM-based routers available, many of the support foot routing.
You can also search for official hiking trails in OSM. waymarkedtrails.org is a great OSM-based source for all kinds of trails (hiking, cycling, mtb, riding, ...) and offers GPX downloads.
Comment: Note that OSRM doesn't support route relations out of the box, which limits its usefulness for some hiking and cycling uses. There are a couple of possible approaches to solve this.


difference equation, LTI system, Z-transform, impulse response

Question: exercises 2 and 3 instructions are in picture

Here is a z-table that I can use to make inverse z-transforms

I did questions 2a and 2b, but I don't know much about how to do the final 2c (I got stuck there)
I did exercise 3 and drew the block diagram as best as I understood it.
I could use maybe some help for 2c
2.a) answer
Find H(z) transfer function, and check stability from poles (inside unit circle or not)
firstly try to get difference equation
$y[n]=1/4*(x[n]+x[n-1]+x[n-2]+x[n-3])$
Z-transform both sides
$Y(Z)= 1/4 * (X(Z)+z^{-1}*X(z)+z^{-2}*X(z)+z^{-3}*X(z))$
After factorizing and shuffling some terms I get that
$ \frac{Y(z)}{X(z)}=H(z)= 1/4 * (1+z^{-1}+z^{-2}+z^{-3})=\frac{z^3+z^2+z+1}{4z^3}$
we  see from $4z^3=0 $ that poles are zero so the system is stable (is that right interpretation???)
2.b) answer
impulse response of the system, I think that this means that when we want to get the impulse response of the system, what we could do is maybe inverse Z transform the transferfunction => so we get h[n] = impulse response
I was looking at my earlier notes and there was mention that when input sequence $x[n] =\delta[n]$, implies that $y[n]=h[n] $= impulse response
Can we just plug in the $x[n]=\delta[n]$ and see what comes out for $y[n]$???
with the plug-in technique we just get $h[k]=1/4*(\delta[k]+\delta[k-1]+\delta[k-2]+\delta[k-3])$
with the inverse Z-transforming the H(z) technique, I get as follows
$(H(z)= 1/4*(1+z^{-1}+z^{-2}+z^{-3})) $
I think, we are supposed to identify
$z^{-k_0}*1 = z^{-k_0}*X(z)$
from the z-table, and also use linearity of inverse-Z-transform to each sumterm
applying the identities from the z-table, we should get
$h[k] = 1/4* (\delta[k]+u[k-1]\delta[k-1]+u[k-2]\delta[k-2]+u[k-3]\delta[k-3])$
looks like basically the same answer, I don't think those unit steps multiplied change the result that much, except ensure causality, but regular deltafunction should also be zero, at negative indexes
2.c) answer
I think one tactic might be to Z-transform unit step $Z(u[n])=\frac{z}{z-1}=X(z)$
multiply that with transfer function, and then you get Y(z)
inverse Z transform should give output sequence...
$Y(z)=H(z)*X(z)=\frac{z^3+z^2+z+1}{4z^2(z-1)}$
I got stuck at that inverse-Z transform... Can you at least verify that the Y(z) is correct at this stage? I think Ive used this same tactic of inverting from the Z-domain into the k-domain to get the output sequences but sometimes I get stuck at the inverse Z-transform...
with the plugging in technique you just get
$y[k]=1/4*(u[k]+u[k-1]+u[k-2]+u[k-3])$
3. answer
Fibonacci
This was goddam difficult also to do.
first start by Z-transform both sides
$Z(y[n+2])-Z(y[n+1])=Z(y[n])
$
$Y(z)=z^2Y(z) -z^2-z-zY(z)+z $
$Y(z)=z^2Y(z) -z^2-zY(z) $
$Y(z)=\frac{z^2}{z^2-z-1}$
Then our teacher gave us tip that we should divide both sides by z, so that it maybe helps to find partial fractions expansion such that we find something in the z-table.
So, first divide both sides by z, and also solve roots of the denominator polynomial $z^2-z-1$ , in order to factorize
$Y(z)/z= \frac{A}{z-b}+\frac{B}{z-a}= \frac{z}{ (z-\frac{-\sqrt5+1}{2}) (z-\frac{\sqrt5+1}{2})  }$
so that
$a= \frac{\sqrt5 +1}{2}$
$b= \frac{-\sqrt5+1}{2}
$
for the partial Fraction coefficients in capital letters, I obtained with the "equating coefficients technique" something very ugly as follows
$A=\frac{-\sqrt5+5}{10}$
$B=\frac{\sqrt5+5}{10}$
Then, finally we can have
$Y(z)/z = A/(z-b)+B/(z-a)$
$Y(z) = Az/(z-b)+Bz/(z-a)$
from the z-table we can identify exponential function j^k == z/(z-j)
$
y[k] = A*b^k+B*a^k
$
I'm too lazy to even write that out but I checked that fibonacci y[k] with my calculator and it seems to work, where k>=0.
I was pretty mindblown by the idea that Fibonacci recursive sequence can be made with explicit formula like this,though...
I had to google about that fibonacci block diagram because I didn't understand what is the input sequence x[n] with fibonacci.
But, apparently you can model the fibonacci system if you put x[n]= unit impulse = deltafunction
so then the entire difference equation changes its form slightly from the recursive definition as such...
$y[n]= u[n-1]*y[n-1]+ u[n-2]*y[n-2]+\delta[n]$
But, I tabulated some values from  n = [-1,0,1,2,3,4,5...] and it seems to be same as the regular fibonacci values
Answer:
elite level block diagram drawn with paint3D...
I wish I had a program that could easily draw these kind of schematics/block diagrams in nicer style...


Insectoids and the concept of 'eating well'

Question: In this project of mine a species of sapient, spacefaring insectoids exists among humans and humanoid species. The insectoids are puzzled by something in humanoid cultures- specifically the idea of eating and drinking for pleasure and not just for survival (the insectoids have a sense of taste but in their minds it's more about alerting them to whether something is poisonous or not)- notions of 'flavour', gourmet meals and people of upper social strata enjoying 'better food' than the rabble are confusing to them- does this sound like a likely attitude sapient insectoids might have?
Comment: I'm not exactly sure what's preventing you from making them pure practical eaters. I mean, beyond the fact you're the one to choose what they are like, it's not like we have many sentient insectoids to compare with yours ^^. Do you know something we don't about your world?
Comment: **The decision is driven by the plot if it's not driven by their biology.**
Without a science-based character to the question either answer will serve your world. The answer is "yes" if the conflict between insectoid and human over eating habits is a core element to your plot. The answer is "no" if your plot is focussed on other inter-species relationship items and such a tase difference would distract us from your story. So, tell us how this species "taste differentiation" moves your story, and we can gladly answer if the eating habit "makes sense." We may even make it "make sense" for you.
Comment: VTC as opinion-based. The existing answers already show this. One can argue that insectoids indeed have no need to enjoy food like we do, but their sapience might eventually lead to individuals starting to pay more attention to it. At that point it is a matter of biology: do your insectoids have sufficiently articulate taste buds? Which is completely up to your design of them.
Comment: As Joachim suggests, how could this be anything but opinion based… but in any case, why would you worry? If you want to write every word of that exposition as gospel truth and part of the laws of physiology spring from chemistry or evolution who would doubt your right to write it that way? It's your world.
Comment: This came to my queue for the reasons I stated above. Perhaps you need more time to think about how it should be rephrased, and I will allow it, hoping to place the question on hold. In the mean time, it would be a benefit for you to visit the Factory Floor or place the question in [the Sandbox](https://worldbuilding.meta.stackexchange.com/questions/9981/sandbox-for-proposed-questions) for development. I will vote "Leave Open" this time only, so you have time, and encourage other voters to leave helpful comments as well.
Answer: Up to you
At first glance this may seem like an opinion-based question. On second thought, if you wish to base those aliens on actual insects, this will vary by species.
Among bees, there is a special kind of honey called royal jelly that is fed only to larvae of queens.
Spiders are not insects, but they are bugs as well. Many weaving species will eat their own web if they can't catch anything. Less nutritious than prey, but at least they don't starve right away.
There is also an herbivorous species of spider (no, really!) that will sometimes eat ant larvae, maybe for the extra protein content.
So the existence of bad but edible food, good food and better food does exist among arthropods. How they deal with it depends on how their society is structured. If your aliens evolved from social insects with a royal caste such as bees, then it's a no-brainer: what they eat makes their very identity within the hive.
However, they might also come from social insects such as carpenter ants or some other farming ant species that only eats one thing ever. Many ants grow fungi in their nests and eat bits of the fungus and nothing else. This would make them feel like anything else either tastes bad or is inedible.
If you do want them to deal with food differently from how humans do, it's up to you. This would make them more alien to us and might make for some interesting worldbuilding.
Answer: Yes it does
As with all xenocultures, what is normal or promoted in one does not necessarily need to be understood by the other, humans having a desire for pretty or tasteful food is no difference. Insectoids (klackons?) only need to eat "enough", they don't need to make a cult from their food, especially since normaly their food has quite some capability of eating them instead. Surely they would be puzzled, especially if they are also eusocial, having no other pleasure than to serve the hive.
Answer: Food quality doesn't matter only by taste but also by nutritional value. The "rabble" eat fast-food; the "rich" eat salads and grass-fed meat. "Rich people's food" is more consistently healthier than it is tastier. Maybe your insect people have underdeveloped taste buds, which still means that they can find the concept of eating for pleasure exotic, but that doesn't mean their food would be the same across strata. You can still have an elite fed on "royal jelly" while the rabble gorges itself on trash - for purely practical and survival reasons.
If anything, what they could be truly puzzled about is how humans become so enthralled by food of subpar nutrition and develop all kinds of health problems by eating them (addiction, diabetes, obesity, etc.). They wouldn't easily understand that junk food is optimized for taste to the detriment of everything else. It would be similar to our amusement at bugs seemingly loving to fly towards light which kills them.
Comment: Historically tis also been seen that rich eat refined white bread and white sugar while the rabble eat wholegrain and raw foods, your point on nutrition vs social strata is lovely but the human drive for … elitism or artificial differences might confound yer data.  And the aliens too, actually, might be hysterical ta explain that flip to em haha
Answer: As @Tortliena said in a comment to the question: practical eaters...
Their sense of taste could be adjusted to strongly favor what they truly need to survive (and thrive physically). That gives them a competitive advantage over species that strongly favor food and beverages that make them feel good. The latter can be dangerously misleading when it comes to food choices. Example: humans.
These preferences cause at least two problems among our species: obesity epidemic, and adverse effects of cravings. The latter one is a problem under severe conditions where resources necessary for survival are transferred to produce and consume enjoyable things... whose return value is too often, let's face it, negative.
Eg. sometimes the actual problem about moonshine has been that people have been short-sighted and used grain to make booze, leaving them hungry later on during the harsh winter. And sometimes the booze was distilled too hastily, leaving too much methanol in it, causing problems of its own. And, many people can be bribed as easily as just by providing enough enjoyment, and it is more likely to fall for it if the situation is not enjoyable. Threats to survival, all because of craving for enjoyment.
If you are a practical eater, things like this don't happen.
From their point of view, our need to enjoy (even occasionally)  what we eat and drink is a liability. They look down to us, not because of what we consume but what it indicates.
Comment: But we are already a species with a sense of taste adjusted to strongly favor what we truly need to survive. It just happens to do so by associating nutrition with tastiness. The senses steer to and away through pleasure and pain, which can always be hijacked
Comment: @Mutoh That is how evolution this time happened to do i heret: it associates the good stuff with pleasure.

Therefore we over eat and we drink too much the tasty stuff, and we actually care so little about the healthy that we have to have reseach, professionals and doctors and clinics, and still billion dollar sugar and drug industry thrives and people are overwheight and diabetes is rampant.
Comment: Evolution could have chosen to make things taste motivating, and only as long as it is needed. It would be like going to toilet, but the opposite. You do it because you need it, and you stop it when it's done, and then you continue what you were doing, and you take for granted that it was not necessarily pleasant, and that  is ok as long as it's not too gross.

We cannot do that. They might see us as creatures who only eat restaurant level food because to them we do. It is a liability.
Comment: That already happens, too: when you need food hunger motivates you to go after it, and you feel full after having eaten enough which is not necessarily pleasant. And try holding poop in for too long and your body will "punish" you with pain, but once you evacuate you'll be "rewarded" with pleasant relief. These senses don't need to be sophisticated because pooping is quite straightforward, but with eating your body has to make sure you pick quality food over, say, sand and ice. It's always the carrot and the stick, just more or less convoluted. The alternative to senses is reason.
Answer: Impossible to say, until insectoids are better defined
The answer depends on other aspects of their physiology and culture.
We enjoy eating tasty food because it evokes pleasant feelings. Can they experience physical pleasure? Can they experience pain? If they can't, many other aspects of our culture will be out of their comprehension.
Wee eat expensive food because it's an attribute of a high social status. Do they have this concept in their culture? If they don't, other impractical expensive things will confuse them.


Yeoman/JS: Repeating HTML blocks in a HTML template - compiling to eventually integrate with Wordpress?

Question: Right, so i'm currently working on a project that will eventually be powered by a Wordpress back-end, but on the front end, will be heavily powered by CSS3 and JavaScript - perhaps even taking advantage of history API and dynamically loading in of content via AJAX.
I'm currently working on the static HTML templates, getting the layouts right, getting all the JS required for the interaction and navigation between pages etc. I'm currently using Yeoman as a watch server to compile my SASS templates and merge all JS modules using RequireJS.
Everything's going fine, but i'm starting to notice i'm repeating a lot of HTML blocks in the HTML templates, and it's not very efficient - i want to just edit the block in one place and have it repeat however many times i need on a page - headers, footers, single blog items on blog listing pages etc. while i'm scaffolding the front-end templates.
Essentially, what i'd like to do is have block templates, that i can import into a parent file, loop through to generate the files i need, and once i'm ready to power the final markup by Wordpress, i can just build the project, export the static HTML files, along with the compiled JS and CSS3, and then break down the HTML into a Wordpress build at the very end.
How am i best going about this?
Integrating Jade? Using Handlebars? I'm not really too bothered about the shortened syntax Jade offers, i just want to be able to compile vanilla HTML from templates while i'm scaffolding. Perhaps something like Jekyll? Is there a node based version?
Is this even the right way to go about things? I have considered generating all my front end from JSON, and during the Wordpress integration, expose the JSON API within Wordpress, but generating all the templates in the DOM won't yield any SEO whatsoever, which is a concern.
What do you guys think?
Comment: I've posted a similar comment in the Yeoman Google Group https://groups.google.com/forum/#!topic/yeoman-dev/epNSoDW4frE
Answer: I've been looking for exactly the same thing. Being used to using jekyll for html pre-processing I assumed Yeoman would naturally support layouts and includes.
Unfortunately it doesn't https://github.com/yeoman/yeoman/issues/700
Not to say it doesn't work, but I have tried using yeoman-jekyll and after an hour of battling with it on both OSX and Windows found it not to generate as comprehensive a gruntfile as the default Yeoman init build.
You mentioned Jade, I'm not clued up on it but this looked like a handy post: Integrating Jade in Yeoman's server/watch/reload tasks
Keep it simple, I wish I did!


Disable action bar aniation during a view navigator transition - Flex Mobile?

Question: does anyone know how to disable that slide animation and just have the action bar instantly change to whatever action bar the next view contains, but still do a slide navigation for the rest of the view. My Action bar doesn't change on every page so seeing the same image reload repetitively in the action bar. Thanks!
Answer: I've just had to solve this as the previous answer didn't work and its not really solving the problem.
So here is the fix.

Extend whatever effect you wish to use. e.g. SlideViewTransition
add the following lines to your extended class import import mx.core.mx_internal; and use namespace mx_internal;
Either inside your constructor set the value (if you don't wish to change it at runtime) or create a setter to modify the value actionBarTransitionMode to = ACTION_BAR_MODE_NONE
When pushing or popping the view, use the created transition.

Without making the answer wordy this is enough info to answer the question but should you wish more information then you can find it here http://kennethsutherland.com/2012/07/11/stop-the-mobile-actionbar-from-transitioning/
Answer: I had this problem myself too.
This is the solution I used.
I moved all the objects in the navigatorContent, titleContent and actionContent from my views to my ViewNavigatorApplication.
Then I defined a state for each view in that ViewNavigatorApplication.
Next I used the includeIn on the content I moved from my views, and assigned the right state to it.
Now you can use events from the transition from your views to update the state ViewNavigatorApplication.
<code><s:ViewNavigatorApplication ...>
    <s:states>
        <s:State name="customerView"/>
        <s:State name="productView"/>
    </s:states>
    <s:navigationContent>
        <s:Button id="thisButtonOnlyInCustomerView" includeIn="customerView"/>
    </s:navigationContent>
    <s:actionContent>
        <s:Button id="thisButtonInBothViews" includeIn="customerView, productView"/>
    </s:navigationContent>
</s:ViewNavigatorApplication>
</code>
That is a rough example of what the ViewNavigatorApplication will look like.
Since the ViewNavigatorApplication doesnt slide, your actionbar content wont slide along with your view.


Why did Klaus Michelson kill his father?

Question: I have seen the season The Originals and in the end Klaus Michelson killed his father. I can't understand why he did this.
Answer: Because he needed "Viking ash" to make the weapon to kill Dahlia. Where else they can get Viking ash? Do they have enough time to search?
So Klause did what he felt right, burning a Viking to get the ash and first he is, not his real father and second whole life he tried to kill Klause so it was not so tough decision.
Comment: He also killed his other father, the question is probably about that. Especially given that the reason he stated did seem bogus, and that later he ignored that other people also qualify for that reason and did not kill them.


Is it a bad idea to CHMOD 777 all the files on your site?

Question: I think i heard that it might pose a security threat to your site, is that right? Makes it more vulnerable to it getting hacked?
How should I undo this, which files should be chmod to what number?
Comment: How is this a WordPress question?
Answer: My original comment:

Is chmod 777 a good idea? if it's not absolutely necessary (which if
  your server's users and groups are properly configured it's usually
  not) then avoid it. is it as terrible and the omg you're gonna get
  hacked any second now disaster everyone makes it out to be? not quite,
  but again it depends on your server config. someone has to get to the
  directory and file ON your server to do damage. anyway, consult your
  server admins for proper permissions (assuming you're not the admin!).

and your follow up question:

So i should ask my web host about this? I thought there would a universal permission configuration, especially for wordpress....

Yes, you should ask your host if you are unsure. WordPress does have a universal configuration, in the sense that permissions must be such that WordPress is able write to the filesystem. The variables are how users and groups are configured on a particular server regarding the webserver software, php, and you as a user.
Answer: Whether your website is based on WordPress or not this is a very very bad idea.
Comment: Is chmod 777 a good idea? if it's not absolutely necessary (which if your server's users and groups are properly configured it's usually not) then avoid it. is it as terrible and the omg you're gonna get hacked any second now disaster everyone makes it out to be? not quite, but again it depends on your server config. someone has to get to the directory and file ON your server to do damage. anyway, consult your server admins for proper permissions (assuming you're not the admin!).
Comment: How should I undo this, which files should be CHMOD to what number?
Comment: So i should ask my web host about this? I thought there would a universal permission configuration, especially for wordpress....
Comment: @Milo: You should really post that as an answer.
Answer: Yes it is almost always a bad idea, unfortunately sometimes it is the only option left. The more complicated permissions can be done with ACLs, which I would prefer to chmod 777.  I work as a Linux Systems Administrator, and there has only been a few specific circumstances chmod 777 was required.
I assume your running *nix, and /var/www is your webroot.
to reset the site to sane permissions, I would run.
find /var/www/ -type d -print0 | xargs -0 chmod 755
find /var/www/ -type f -print0 | xargs -0 chmod 644

this  assumes your webserver runs as a your normal user.
If your webserver runs as the user "jonsmith", and your user:group is jonsmith:jonsmith  then this is, although not the absolute best, better than chmod 777.
If your webserver runs as the user "www-data", and  your files are placed by your system user "jonsmith" then i would run this also.
chown jonsmith:jonsmith -R /var/www/
chown www-data:www-data -R /var/www/wp-content/

this would make just your wp-content directory writable by the webserver.
You will have to change those names/webroots to your situation.
This should push you in the right direction.
Answer: yes its the worst idea ever. one example:  this is why i see customers coming in stating "my server is sending lots of email from firstname.lastname@example.com" ( replace hostname with the server name ) had one today, with 389000 porn related spam emails in the mail queue. sending from a user called anonymous@hostname which was actually the user www-data ( apache ) i did a bit of work and found the site that was compromised and it had an includes directory that had everything set to 777 permissions including a php mail form. then i had to go through and install qmail-remove since qmail does not have a native script for flushing the mail queue.... needless to say this isint in my job description... but the customer was incredibly happy.
if you have hosting some place check permissions of the files if you see something like root : root change this to user : apache or user : www-data then the issue should go away. and you should be able to run with octal permission values of 644. on a side note.... for the love of god people fix your php date.timezone!!!!! its annoying to see in the logs. and it takes two seconds to change.
Answer: It's a terrible idea. 777 allows read, write,  and execute privileges to anyone and everyone. Do I need to explain why this is a bad idea?
Comment: Yes you do, because your current answer is a little confusing. Anyone / everyone *shouldn't* be able to reach the stage where they can write or execute something that they are normally not allowed to. But if they do, it's because of badly written scripts. More restrictive permissions can prevent the attacker from removing or executing certain scripts, but he will most likely still be able to upload his scripts somewhere else and execute them


wind turbine voltage multiplier

Question: I am building a wind generator with a car alternator without a gearbox.
I know that the alternator is designed to spin at 5-10k RPM and the blades runs at 60-120 RPM so the alternator generates less than 1 volt.
My question is: Can I use a voltage multiplier such as a Cockcroft-Walton generator to get useable voltages at reasonable efficiencies?
Comment: To be clear, you can convert your voltage, up or down, but a CW multiplier is probably not the best way to do it.  Motor/generator design/selection will have an impact on performance.  Disc generators are popular DIY windmill solutions, and you can also repurpose many other kinds of motor if you want to run directly at low speed.  If you are fond of the alternator, adding a gearbox, despite the losses in the gears.  For brushless permanent magnet motors anyway, you're be looking for low kV ratings.  I suspect motors from those explodey "hoverboards" would be good.
Answer: You probably need to connect your field winding up to get more output but running at this dismal speed is going to be a poor generating solution. No, a cockcroft walton multiplier won't help much here because they need several volts p-p to make any headway due to the internal diode volt drops. Drop the idea of the CWM and stick with understanding how to set the field winding current. I believe a lot of automobiles use the field winding current to control output voltage hence the final alternator output is regulated.
If you are not using the field winding then you are relying on residual magnetism in the rotor for generating your output voltage so it will be low.
Comment: All alternators use the filed winding, the question is: Is the OP using a self excited alternator or a separately excited alternator.
Comment: So I need to work on the field winding current but i'm worried about the fact tha the field winding could absorb more energy than it produces
Comment: P.S.My alternator is separately excited
Comment: Don't worry about it, try it. If it used more that what is produced then that's because it isn't rotating and it would be a poor generator if it did that when spinning.
Answer: Alternators on cars need 2000 to 2500 rpm to begin charging, this is why the pulley diameter is about 1/3 of the crank pulley.
Also the ratio of the pulleys is chosen so the max rpm of the alternator is not exceeded at max engine rpm - the rotor can contact the stator and seize since the clearance is minimal...
You should look at gearing or making your own alternator.
Here is a link to some really good information about making wind turbines, and yes, this guy has been there and done it...
http://scoraigwind.co.uk/a-wind-turbine-recipe-book/

wind turbine voltage multiplier


Disk replacement

Question: My son accidently made a serious scratch in disk #1 on his licensed copy of GTA 5 and The game can't be installed on his pc anymore.
Is it possible in any way to buy a replacement disk in order to complete the installation, and in case, how do I get one? Or do I need to buy a complete new version of GTA 5 for him?
Comment: Contact Rockstar Games and show your copy of the game and ask for a digital download.
Comment: Don't you have to redeem the copy on Steam anyway? If so, you can just download it from there again, no DVD required.
Comment: I never got that far. He came to me with a physical copy (3 DVDs), given to him as a present.
Comment: @P1raten: could you link me to the right department at Rockstar, please ?
Answer: While they mention in a couple of their Rockstar Support Articles about a disc replacement policy, I can't find anything specific about it. You will probably need to contact Rockstar directly and explain the situation.

However, you can use the Rockstar Activation Code that comes with the game box to redeem a digital copy of the game. Below is the link to the Support Article, along with the relevant Q&A.
https://support.rockstargames.com/hc/en-us/articles/205359647-Support-For-GTAV-PC-Owners-to-Re-Download-GTAV-As-a-Digital-Copy

Question: If I buy a new boxed version of GTAV PC with DVD discs, can I use the Rockstar Activation Code in the box on the GTAV PC Social Club Activation page to download the game instead of installing from the discs?
Answer: Yes. When you use a Rockstar Activation Code to activate a copy of GTAV PC, your Social Club account becomes entitled to access the game, whether you choose to install and use the DVD version, buy the game from a digital retailer that hosts its own GTAV download, or download from the GTAV PC Social Club Activation page. Also, the Rockstar Activation Code included in a new physical version of GTAV PC can be used to download the game from Social Club (for example, if your Internet and DVD speeds mean downloading would be faster than installing from discs; or, if you accidentally damage one of your discs in the future).

Disk replacement


Icons missing/changed when switching back to the default desktop environment from KDE Plasma on Ubuntu 20.10

Question: So I have an Ubuntu and Windows dual-boot on my computer, and I recently installed KDE Plasma (using sudo apt install kde-plasma-desktop) as another desktop environment I could use. I switched over to it for a while and decided to come back to the one labeled "Ubuntu" on the login screen. After logging back in I noticed that a lot of the icons have been set to the ones in KDE Plasma. I've tried to change them back using GNOME Tweaks and changing the icons pack, but that really on fixes the one for LibreOffice and a few others. The Ubuntu Software Center's icon is the default application icon or a transparent square no matter what and a lot of the apps that were included in the system have been changed and I can't seem to get them back to default. I'm still somewhat new to Ubuntu, so the answer might be really obvious.
Answer: You can install and run gnome-tweaks. It permits to change back icons themes under appearance menu.
sudo apt install gnome-tweaks

Answer: Okay, so I actually fixed this 6 minutes after asking this question. What you have to do is log onto KDE Plasma and go to "Icons" in settings. Then you need to change the icon pack to Yaru.
Comment: I find it strange that an icon setting in KDE does affect an icon setting in Ubuntu desktop: normally that should not interfere.
Comment: @vanadium I don't know why it's happening, as the Cinnamon DE doesn't affect the regular Ubuntu icons.


Why question ban is not removing after editing the old questions properly?

Question: Currently I can't ask questions in my Stack Overflow account. So I followed the given instructions and edited my old posts. But still I can not ask questions on the site. Please can I know what should I do to avoid this question ban. Any suggestions will be appreciated.
Comment: Have you undeleted and improved your previous questions?
Comment: @hims056 : No I didn't undeleted my old posts. I just modified the remaining posts. Thanks for your suggestions. I'll try on them.
Comment: Ultimately editing is only a means to an end, you need upvoted to escape the ban
Answer: Deleted posts still count towards the ban.
Simply deleting them means you cannot improve them and never get out of the ban.
Undelete and improve those posts. Get them upvoted and you will eventually get out of the ban.
Comment: @M.NightDemonbobby - Where do you see such information in my answer?
Comment: @Su1 just be careful now, you are probably still at the edge of the ban. Think thrice before hitting submit button :)
Comment: I think this information should be extended and added to the FAQ entry, as at the moment it does not contain any information on how to retrieve deleted posts.
Comment: @Mołot : Thanks for reminding. I thought all was over. I'll be careful before posting anything in stackoverflow. Because I learnt a lot from this site and got helped whenever there wasn't any resource to help. I'll try my best to contribute positively to the site.
Comment: I meant the "undelete and also improve those" part, extended with a "how to undelete stuff, look at this". Bad wording on my part, sorry.
Comment: Thanks all who supported. I just checked my account. It has got some reputation score and the question band was removed.
Answer: I would say that the best way to get out of the question ban is to write a lot of good answers. That's because writing answers gives you a "fresh start." It's a bit like fixing "bad credit:" Start paying your most recent bills on time, and the impact of past mistakes will fall by comparison.
Editing/improving old questions might work. But they are subject to "legacy" issues. Editing questions works best if the new versions draw upvotes. It might work against you if they draw new downvotes.
One thing I'm not sure of: If you change a lot of obviously low quality one-liners into whole paragraphs, will the system remove some of the stigma for very low quality posts? If I were writing the algorithm, I might program, "one liner plus downvotes equals very low quality." But that's just me, and I'm not at all sure that it reflects the site's priorities.


Lever action or primitive Bolt for an Army modernizing at speed?

Question: About what is says on the tin. There's this Empire, which for our purposes has a general industrial capacity somewhere around that of 1910s Imperial Germany, but which for various has long neglected improving the main weapons of its armies above the level of smoothbore muskets / percussion caps. Now finding themselves fighting a far larger, probably far longer lasting war with a technologically superior adversary which does have 'modern' bolt actions, which of those two paths outlined should they take if they want to modernise as much of their sizeable army as possible? Assuming that the technical ability to make either lever actions or early bolt actions exists, and that industry can be mobilized to make it.
Comment: What is the difference between primitive and modern bolt action rifles. What is the objective of the weapon modernization program. How is the ongoing conflict being fought? Will new rifles come with changes to doctrine or will it remain as is? Are we to consider procurement costs, or just the functional aspects of the weapon?
Comment: In real life, what rich and powerful countries do when they want to update their small arms is to put out a list of requirements and evaluate the designs submitted by inventors and manufacturers. (Examples: [Russia 1889](https://en.wikipedia.org/wiki/Mosin–Nagant), [Germany 1870](https://en.wikipedia.org/wiki/Mauser_Model_1871), [Germany 1888](https://en.wikipedia.org/wiki/Gewehr_1888).) The point is that what you want is not a perfect rifle, but a good enough rifle *which somebody can actually manufacture by the millions*, and in a short time.
Comment: Best for what? speed, accuracy, cost, ease of use, compactness. there are trade off for everything different militaries will make different decisions based on different doctrine and preferences.
Comment: Whats the ammunition capabilities as well? Bolt-action designs only really gain significant benefit with high velocity ammunition, with a clip or disposable magazine loading.
Comment: Also, what do you mean by 'early' bolt actions? A Mauser 1898 family has pretty much all the core features of an action which served in to WW2, the Lee-Enfield action was developed in 1895.
Answer: There's two answers here, the Historical Answer and the Answer I'm going to give
So, the Historical Answer - Everyone in WW1 went with a Bolt Action.
Why?
A myriad of reasons, but I'll give the abridged version:

Rifle Cartridge cases vs straight-walled Pistol-esque cartridge cases
Firing from the Prone position
Price (Bolt actions are generally easier to manufacture)
Doctrine of massed-volleys at formations beyond the range one could reasonably engage a single target
Hunting experience in Africa with various Game cartridges
Reloading from Stripper (ooo-er!) clips vs reloading a Tube Magazine.
Better accuracy
Able to handle higher pressure cartridges due to the locking lugs.

So, the 'Correct' answer is a Bolt Action.
However, There is much debate in the Firearms community around WW1 and would Lever actions have been a better choice. A lot of the decision making around the choice of Firearm was centred around getting impressive looking groupings on the range and in Competition - which although is nothing to scoff at, isn't always applicable in warfare.
My Answer is a Lever Action
To clarify - I own (among others) a 1949 SMLE Mk4 in .303 British (the same Rifle used by the British in WW1) and I own a Lever-Action in .44 Magnum.
The Lever Action is a Brush-Gun, that is for hunting Game Animals (Goats/Deer) in thick brush/forest - where a Rifle Calibre potentially could ricochet off of a Branch, whereas the .44 Magnum will punch through a branch (even though the .303 has significantly more muzzle energy - it's to do with Bullet shape and weight) - and it's not used for taking shots at distances much further than 100 metres.
Given your time period, Optics aren't really a thing except for a few Sniper units and even WW1 optics were 1-3 power IIRC. Which means your realistic engagement distance is going to be less than 400 metres - And Trench Warfare (assuming it happens) is around 100-200 metres - so something like a .44 Magnum is going to be at home here (could go for a different calibre - a 5.56 with a Lever Action would be ideal... but 5.56 doesn't exist at this time)
Now - the SMLE, notorious for being able to throw some serious lead down-range, especially if you use the Aussie technique of your middle finger on the trigger and keeping a hold of the bolt handle. It takes a bit of practice, but the British demonstrated in WW1 that with average infantry soldiers, the rate of fire that could be achieved was impressive....
It's even easier for someone with a Lever-Action to get rapid follow-up shots. and get serious speed. Reloading is a bit trickier having to single load cartridges rather than a stripper-clip - however, you should have dealt with all the immediate threats with your initial magazine dump.
Firing from Prone - yes, it's still a concern, but not as much, so I'm kinda skipping this.
In short - the main thing that a Lever Action has an advantage is a significant Rate of Fire increase, even for an inexperienced shooter over a Bolt Action.
The Draw-backs for a Lever-action when looked at with hindsight aren't that big of a deal as a lot of Military thinking going into WW1 was... 'Wrong' - which is why after WW2 when they actually studied this, they realised that full-power Rifle Cartridges were too much bang for the engagement distances, thus the intermediate cartridges were born.
Plus... Bolt actions are fun and all, but get a Lever Action and flog it at full speed and you will have a big ol' smile on your dial
Comment: @JBH - here ya go: https://soldiersystems.net/wp-content/uploads/2023/01/img_9515-600x234.jpg Just imagine that with Copper and Bronze
Comment: @JBH this https://armourersbench.com/2019/08/11/browning-prototypes-detachable-box-magazine-lever-action-rifle/ this https://armourersbench.com/2020/12/19/john-brownings-1895-slide-action-prototype/, or this https://armourersbench.com/2019/11/03/john-brownings-1892-en-bloc-lever-action-prototype/ maybe ?
Comment: Or you could simply go with both. Issue a magazine fed lever action rifle like the Savage Model 99 or the BLR to line troops and issue bolt action rifles (low rate production) to sharp shooters and snipers.
Comment: I like this answer. In fact, I can't think of a reason why you couldn't have a magazine-fed lever-action rifle with a slightly longer (maybe +125mm) barrel. Given the time period, you could unload rounds faster than a bolt action would allow. It'd scare the crap out of the enemy and have a great steampunk vibe.
Comment: Now we're talkin! Archmagos! This would be *awesome.*


Oxidation of methane

Question: In the reaction $\ce{CH_4 + 2O_2->CO_2 + 2H_2O}$ the $\ce{C}$ atom is oxidized. I can clearly see the addition of $\ce{O}$ atoms, however I don't see a change in Oxidation state. In the products, $\ce{C}$ oxidation state (O.S) was +4, and in the reactants, $\ce{C}$ O.S is +4. I believed an oxidation meant an increase in oxidation state.
What am I missing?
Answer: Actually in $\ce{CH4}$ with slightly more electronegtaive carbon it is in $-4$ state. With $\ce{CO2}$ the oxygen is more electronegative oxygen carbon is $+4$. Therefore oxidation is also defined as addition/replacement of a more electronegative element.

Electronegativities $$\begin{array}{}\bf H&2.2\\\bf C&2.55\\\bf O&3.44\end{array}$$

Oxidation of methane


Will Ubuntu work if I install it offline?

Question: I´m going to install Ubuntu 12.04 on my laptop, and I don't have internet at home.
I know that I can install it without internet, but , does it work?
Comment: Definitely. When you get Internet connection, just type `sudo apt-get update && sudo apt-get upgrade` on the terminal.
Answer: Yes it will work, however with some restrictions.  For example there are "Must do" updates if you want to play MP3s or movie files etc. (Ubuntu Restricted Extras).
Also you need to install medabuntu libraries if you need to play DVDs.  There are others but apart from these restrictions Ubuntu will work.
I had to to this once and was able to update everything at a later date
Answer: As everybody say, you can install Ubuntu 12.04 offline but there will be a lots of packages, updates and softwares that you may need.
To solve this problem, you have different ways to install software and package in a computer without a Internet connection.
One option is Keryx, a portable package manager. Keryx offers to you a nice GUI making easy to use it. And, as if it were not possible to be better, it's open source!
How it works?
You download the package that you need in another computer with Internet connection and then install it in your computer offline.
You can download Keryx from their official website. This software support 32 & 64 bits architectures.
A screenshot:
Comment: @StephenMyall From another computer with Internet connection.
Comment: ???? How can he download Keryx with no internet?
Answer: Absolutely, you just wont get the updates at the time of installation.
Comment: and when I get connected it will update?
Comment: yes you will be able to update after installation just check for updates and install.  I it this way so the installation goes faster, then after install I can update and install the Restricted extras and ect. That way I can use the computer and let the updates install
Answer: You can install Ubuntu without an Internet connection.
From my experience it is not good idea to install Ubuntu offline, some third-party software needed to install from source or script which will cost you extra trips to get the missing packages.
Answer: As an alternative to Keryx, you can use apt-offline or apt-offline-gui.
Pre-requistes: A friend's system with Internet connection. apt-offline installed in both your systems.
The Offline installation is achieved in 3 simple steps.
Step 1:
Generate a signature file on the Disconnected Debian box at home
apt-offline set /tmp/apt-offline.sig
The above command will generate all information required from apt about updating its database.
Step 2:
Download data based on the signature file generated earlier
apt-offline get C:\apt-offline.sig --threads 5
The above command will download data as mentioned in the signature file. To speed up downloads (that can be from multiple apt repositories), in this example we spawn 5 download threads.
Once completed, you could just copy the data (an archive file, if you used the --bundle option) back to the removable medium and copy it back onto your offline host.
Step 3:
Once you're back upon the home Debian machine, you feed the data from the removable medium to apt-offline:
apt-offline install /media/USB/apt-offline.zip
This will update the APT database on your disconnected machine seamlessly.
Apt-offline can be even used in Windows systems. In my opinion, apt-offline is the best option for Offline installation.
Source
Answer: In a single word: Yes.
If you have already burned your ubuntu release at a USB or a CD common sense states that all the files and components of your operating system are included. That happens to any operating system.
Take for instance Windows:
-Are you in need of an internet connection when you install it at a computer through a CD?
-No.
On the other hand if you are going to install using the windows installer (Wubi) which installs ubuntu at your existing Windows partition, you must have an internet connection in order to download the .iso and proceed to the installation.
However you should notice that if you do not have a working connection you will not be able to download any updates(except if you have an old release which is no longer supported by Canonical)  from the update manager. You can always type sudo apt-get update in order to install any updates and fixes to your system.


how to detect 125khz tags with mfrc 522

Question: I have just ordered MFRC 522 RFID reader from amzon, and I have also orders 5 RFID tags with keychains and a arduino uno board for my project, I have received RFID reader and tags and I have tested the tags with my Sony xperia NFC. The tags that I received with the readers are working fine but the key chain ones are not working. I think because of the frequency difference 13.56 MHz and 125 KHz. So, please tell will this key chain tags work with the Reader
Comment: than what would be frequency range of the card/tag the one which came with the mfrc522 reader???
Answer: You are correct NFC is 13.56MHz the key chain ones you are referring to are most likely 125kHz The reader you have will only read 13.56MHz this is the NFC and HID cards. If you want to read the Key Chain ones you will need a reader like this one. Weigand 26 Card Reader Most Phones will not read the 125kHz
Answer: You can buy a 125 kHz reader from eBay for around $7. I got one like this:

You can communicate with it (listen to it) with a single serial pin (plus ground and power of course). I have a post about that board which describes the connections.

So, please tell will this key chain tags work with the Reader

No, the 125 kHz tags won't work with the 13.56 MHz reader. However you can work around this (if you want to) by using the 125 kHz tags with a different reader.

how to detect 125khz tags with mfrc 522


Application for leave

Question: Kindly grant me leave from 14/4/2017 to 20/04/2017 for this I highly obliged to you
Thanks &Regards
Is this the correct sentence to take leave from bos
Comment: this is the first time you've asked for leave, yes?
Comment: No sir this is not a first time when I am leaving
Comment: Are you asking for leave retroactively or in the future?
Answer: It depends on where you live and work.  "Kindly" is not as frequently used in American work settings as it is in India.
Also, you should add "am" in "I am."  As in, "I am highly obliged to you."
Personally, I would write,

Could you please grant me leave from 14/4/2017 to 20/04/2017? I would greatly appreciate it.  Thank you, ...

But I am speaking as someone who works in Chicago, Illinois in the U.S.
Again, it depends on your workplace and culture.  Do whatever is customary in your workplace, if writing it exactly as written is something your boss would understand and appreciate, then it's the correct thing to write.
Answer: Having lived in a country for several years where many of the people I know are from Southern Asia, I think the most common way of writing this would be:
"May you/Could you kindly grant me leave from 14/4/2017 to 20/04/2017? For this I would be highly obliged to you. Thank you and Regards."
I think this is a slightly more formal version of what you said, and I have seen similar methods of writing formally from people I know.
Comment: "May you" cannot be used to form a request, only for an undirected expression of wishes.
Comment: @BenVoigt as I said, I was basing this off of what I have seen people from that part of the world write. It is very common for 'may you' to be used in this context, and this is a good example of how 'Indian English' and 'America/British English' are different, hence why they are considered different dialects on most websites that offer the choice (think Siri).

Application for leave


probability and random variables notation

Question: I have a probability space $(\Omega, S, P)$, where $\Omega$ is a sample space, $S$ is a sigma-algebra, $P$ is probability measure, $P : S \to [0,1]$. Now I consider some other space $(A, B)$, where $B$ is a sigma-algebra on $A$. This allows me to define a random variable as a measurable function $X : \Omega \to B$ such that for every $\mathcal{B} \in B$ I have $X^{-1} (\mathcal{B}) = \{ \omega \in \Omega : X(\omega) \in \mathcal{B} \} \in S$. Finally I can bring in the probability distribution $\mathbb{P}$ which is another measure, this time defined as $\mathbb{P} : B \to [0,1]$, such that for any  $\mathcal{B} \in B$ we have $\mathbb{P} (\mathcal{B}) = P(X^{-1} (\mathcal{B}))$. This is, I believe, a pushforward measure, literally from the definition, correct?
So now I have some question regarding notation, for example in some textbooks I may encounter random variable $X \sim N(0,1)$ and some exercise to calculate $P ( -1 < X <2 )$. My question is what is $P$ in this case? Is it my original $P : S \to [0,1]$, or is it what I've defined as $\mathbb{P}$? Or maybe is it some not-exactly-formal thing to make the notation easier on the eyes?
Answer: In $P(-1<X<2)$ $P$ stands for the original probability measure on $\Omega$. In terms of $\mathbb P$ we can write $P(-1<X<2)=\mathbb P ((-1,2))$ since $X^{-1}((-1,2))=\{\omega \in \Omega: X(\omega) \in (-1,2)\}=\{\omega: -1<X(\omega) <2\}$.
Comment: @gabe Yes, that is a standard notation in Probability Theory.
Comment: Most of the time we don't know what the random variables or the  probability space  and we don't even care. We are interested in probabilities , expectations etc.  and these things depend only on distributions. Life gets lot more coplicated when we start looking  at explicitly defined random variables on a probability space.
Comment: So do I get this right that $P(-1 < X < 2)$ is really $P(\{\omega : -1 < X(\omega) < 2\})$ ?
Comment: Also, I get that the concept of random variable is useful, because we can work with quantities instead of sometimes not so clear elements of sample space. But why do we even need probability distribution? Not in a common meaning like normal distribution, but in a formal sense, like the $\mathbb{P}$ from my original post. Couldn't we define everything, or almost everything in probability in terms of the original measure $P$? I haven't dug that deep into probability yet so I might be lacking the big picture perspective, hence my question.
Comment: do you have any response to that? I would appreciate it


Carnot cycle with varying reservoirs

Question: I was thinking what will happen to the standard Carnot cycle, if instead of - say - the usual cold reservoir, we adopt a smaller refrigerator, whose temperature in fact changes after the heat release from the piston.
My opinion is that in this case the cycle is no longer reversible, am I wrong?
Comment: No you are correct in what you say, but I worded my comment badly, sorry. The idealised Carnot engine with a smaller reservoir will result in an increasing tendancy towards irreversabilty, as you go from essentially infinite volume to finite volume. https://en.m.wikipedia.org/wiki/Carnot_cycle
Comment: Thank you! I think it's the usual problem with idealizations - e.g., from Wikipedia, the reservoirs *"are so large that their temperatures are practically unaffected by a single cycle"* - if we apply literally this concept, even the first cycle would not be perfectly reversible
Comment: Sorry, your question is not clear to me. In the Carnot cycle, the cold reservoir heats up. What "changes" in your setup, except that now  it heats up faster, being smaller in volume. Thanks
Comment: AFAIK (but obviously I could be wrong) the two reservoirs are described as being so large that the addition/subtraction of heat doesn't alter their temperature...
Answer: If the temperature of the cold reservoir (the heat sink) increases with each cycle, the efficiency of the cycle will decrease with each iteration of the cycle. Eventually, the temperature of the cold reservoir will equal the temperature of the hot reservoir and the cycle will stop.

Carnot cycle with varying reservoirs


How do you create a transaction from a UTXO in BitcoinJ?

Question: Is there a way to construct and send a transaction in BitcoinJ without a wallet? I just want to build my transaction from a utxo and broadcast it.
Answer: Sort of. Here's some code to get you started. It creates a transaction with one input and two outputs. One output sends some coins, another one commits some data. However, it still uses Wallet::sendCoinsOffline to complete and commit the TX, but I think you could get rid of it if you understand what Wallet::completeTx and Wallet::commitTx do.
public class App extends WalletAppKit {
    public void commitStatement(String statement) throws InsufficientMoneyException {
        Address addr = getSomeAddress();
        TransactionOutput prevLink = getSomeUtxo();
        NetworkParameters params = RegTestParams.get(); // regtest mode

        byte[] data = statement.getBytes();
        if(data.length > 80) {
            throw new RuntimeException("OP_RETURN data cannot exceed 80 bytes");
        }

        Transaction tx = new Transaction(params);

        log.trace("prevLink TX for '" + statement + "': " + prevLink.getParentTransaction());

        tx.addInput(prevLink);

        Coin feeAmt = Transaction.REFERENCE_DEFAULT_MIN_TX_FEE;
        Coin opRetAmt = Transaction.MIN_NONDUST_OUTPUT;
        Coin changeAmt = prevLink.getValue().minus(opRetAmt).minus(feeAmt);

        // 1st output: send coins
        tx.addOutput(changeAmt, addr);
        // 2nd output: commit some data
        tx.addOutput(opRetAmt, ScriptBuilder.createOpReturnScript(data));

        log.trace("TX for '" + statement + "' before SendRequest: " + tx);
        SendRequest req = SendRequest.forTx(tx);
        // Want inputs and outputs to keep their order
        req.shuffleOutputs = false;
        req.ensureMinRequiredFee = true;

        log.trace("SendRequest for '" + statement + "' before completeTx: " + req);
        wallet().sendCoinsOffline(req);

        // NOTE: At this point, the TX is saved in the wallet!
    }
}

Later edit: So here's an example of how you can modify completeTx and sendCoinsOffline. I actually had to do this today for my own purposes by subclassing the Wallet class. You probably need to take a different route than subclassing Wallet but this should give you an idea of what you need to do.
Warning: This modified code takes care of signing and paying the fee only for these special-kind of transactions with one input and two outputs. Seems to work so far as I've tested it.
public class MyWallet extends Wallet {
    private boolean payFee(Transaction tx, Coin feePerKb, boolean ensureMinRequiredFee) {
        final int size = tx.unsafeBitcoinSerialize().length;
        Coin fee = feePerKb.multiply(size).divide(1000);

        if (ensureMinRequiredFee && fee.compareTo(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE) < 0)
            fee = Transaction.REFERENCE_DEFAULT_MIN_TX_FEE;

        TransactionOutput output = tx.getOutput(0);
        output.setValue(output.getValue().subtract(fee));

        return !output.isDust();
    }

    public void myCompleteTx(SendRequest req) throws InsufficientMoneyException {
        lock.lock();
        try {
            // Print the output value
            Coin value = Coin.ZERO;
            for (TransactionOutput output : req.tx.getOutputs()) {
                value = value.add(output.getValue());
            }

            log.debug("Completing send tx with {} outputs totalling {} (not including fees)",
                    req.tx.getOutputs().size(), value.toFriendlyString());

            // Check for dusty sends and the OP_RETURN limit.
            if (req.ensureMinRequiredFee && !req.emptyWallet) { // Min fee checking is handled later for emptyWallet.
                int opReturnCount = 0;
                for (TransactionOutput output : req.tx.getOutputs()) {
                    if (output.isDust())
                        throw new DustySendRequested();
                    if (output.getScriptPubKey().isOpReturn())
                        ++opReturnCount;
                }
                if (opReturnCount > 1) // Only 1 OP_RETURN per transaction allowed.
                    throw new MultipleOpReturnRequested();
            }

            // Pay for the TX fee, depending on the TX size.
            Coin feePerKb = req.feePerKb == null ? Coin.ZERO : req.feePerKb;
            if (!payFee(req.tx, feePerKb, req.ensureMinRequiredFee))
                throw new CouldNotAdjustDownwards();

            // Now sign the inputs, thus proving that we are entitled to redeem the connected outputs.
            if (req.signInputs)
                signTransaction(req);

            // Check size.
            final int size = req.tx.unsafeBitcoinSerialize().length;
            if (size > Transaction.MAX_STANDARD_TX_SIZE)
                throw new ExceededMaxTransactionSize();

            final Coin calculatedFee = req.tx.getFee();
            if (calculatedFee != null)
                log.debug("  with a fee of {}/kB, {} for {} bytes",
                        calculatedFee.multiply(1000).divide(size).toFriendlyString(), calculatedFee.toFriendlyString(),
                        size);

            // Label the transaction as being self created. We can use this later to spend its change output even before
            // the transaction is confirmed. We deliberately won't bother notifying listeners here as there's not much
            // point - the user isn't interested in a confidence transition they made themselves.
            req.tx.getConfidence().setSource(TransactionConfidence.Source.SELF);
            // Label the transaction as being a user requested payment. This can be used to render GUI wallet
            // transaction lists more appropriately, especially when the wallet starts to generate transactions itself
            // for internal purposes.
            req.tx.setPurpose(Transaction.Purpose.USER_PAYMENT);
            // Record the exchange rate that was valid when the transaction was completed.
            req.tx.setExchangeRate(req.exchangeRate);
            req.tx.setMemo(req.memo);
            //req.completed = true; // FIXME: ALIN: This field is private, can't set it to true, but thankfully this is just for debugging.
            log.debug("  completed: {}", req.tx);
        } finally {
            lock.unlock();
        }
    }

    public Transaction mySendCoinsOffline(SendRequest request) throws InsufficientMoneyException {
        lock.lock();
        try {
            myCompleteTx(request);
            commitTx(request.tx);
            return request.tx;
        } finally {
            lock.unlock();
        }
    }
}


Renting or owning my home?

Question: I have been renting a home now for about 4 yrs. The money just seems to go into the monthly rent and its gone. Would I be better off purchasing and owning my own home. I live off of Social Security income, but have some money saved up and could make a down payment on a home that I could afford the monthly mortgage. Renting seems like a dead end for me. I live in Fontana, CA. The homes in north Fontana are too expensive. I was thinking about buying a home in the Apple Valley area, as they are a lot cheaper. But its the desert area so I dont know.
Comment: We can't answer that. Run the numbers and decide whether (a) you can afford to buy a house that you'd want to live in, (b) whether it's actually cheaper (it may not be, after you've figured everything from insurance to taxes to maintenance), (c) whether you really want to commit to living in that specific place for at least five years, preferably longer... There is no shame in renting, and it is NOT always more expensive. I rented for 25 years, and I bought not because it would be less expensive but because there were things I wanted to do that I couldn't in a rental.
Comment: I disagree with the vote to close. In my opinion, the OP can offer details that members can use to guide his decision. If those details don'e come in say, 48 hours, I'll support the closure.
Comment: [This question](http://money.stackexchange.com/questions/29529/rent-or-own-given-these-circumstances) may be useful, and may give you an idea of the kind of information you need for such a decision.
Answer: I recommend reading What's the catch in investing in real estate for rent? and making a list of expenses.
You have a known expense, the rent, and the assumption that it will rise a bit each year. If not each year, eventually the landlord will bump it, and on average, the rent should track inflation.
The buy side is the complete unknown, especially to us here. The mortgage and taxes are just the beginning. My ongoing issue in the buy/rent debate is that it's easy to buy "too big" or at least far bigger that what you are renting.
One extreme - a couple moves from their one bedroom apartment into their purchased 3BR home with far more space than they ever use. No need to paint the full picture of numbers, the house is a money pit, and they live for the house.
Other end - Couple already renting a nice sized home, and they buy a similar one. They rent out the two spare bedrooms for 5 years until they have kids and want their privacy back. They bought smart, for less than market price, and from day one, the mortgage was lower than the rent they paid. By year 5, having sent the extra income to pay down the mortgage, they've paid down half the loan. As the kids come along, they refi to a new 30 yr fixed at 3.5%, and the payment is tiny compared to the rest of their budget.
Simply put, the ratio of house price to rent for that same house is not a constant. When the ratio is high, it's time to rent. When it swings very low, it's worth considering a purchase. But the decision is never clear until every detail is known. The time may be perfect, and the day after you close, you lose your job, or in a good scenario, get a raise and are relocated. Just because you bought low yesterday, doesn't mean the market will pay you a good price today, it takes time for out-of-whack pricing to come back to normal.
A simple question? Maybe. But we first need a lot of details to help you understand what you are considering.

Renting or owning my home?


Google search console sitemap 404 error

Question: I have a problem with the sitemap in Google search console.
In the index sitemap I see al posttypes with a link to the sitemap from that posttype.

https://www.example.com/wp-sitemap-posts-post-1.xml
https://www.example.com/wp-sitemap-posts-page-1.xml
https://www.example.com/wp-sitemap-posts-product-1.xml
https://www.example.com/wp-sitemap-posts-product-2.xml
https://www.example.com/wp-sitemap-posts-product-3.xml
https://www.example.com/wp-sitemap-posts-product-4.xml
https://www.example.com/wp-sitemap-posts-product-5.xml

I have a lot of product and Wordpress split the xml in different parts you can see above.
If I send the index sitemap called https://www.example.com/sitemap.xml to Google Search Console I get an error.
2 of the product sitemaps https://www.example.com/wp-sitemap-posts-product-4.xml and
https://www.example.com/wp-sitemap-posts-product-5.xml has an 404 error but If I browse to these hyperlinks the files are exist.
Does somebody know this issue?
Answer: You probably need to "flush" your permalinks.
Turn the sitemap feature off, (yaost?), change your permalinks to default and back, turn on the sitemap feature again.
I like using a separate plugin to handle this instead of using Yoast. I don't like their naming convention/structure, and this issue seems to happen a lot.

Google search console sitemap 404 error


Convolution, Fourier transforms, and area preservation

Question: I've learned from this answer that the integral of a convolution f * g (i.e. the area of the convolution) yields the product of the integrals of f and g (i.e. a product of areas):

Af *g = Af * Ag

But from this answer I've learned that convolution corresponds to polynomial multiplication in one space and term-wise multiplication in the dual space.
Now I'm trying to bring together three seemingly different types of products:

Multiplication of "areas" (i.e. of sums or integrals)
Multiplication of polynomials (i.e. of corresponding monoms + summation)
Term-by-term multiplication

I'm lacking the intuition how this is all supposedly the same, i.e. with respect to the multiplication of areas, and how the Fourier transformation comes into all this.
Consider a simple example from this answer:

x[n] = {2, 4, 1} and p[n] = {5, 1, 8}
with areas Ax = 2+4+1 = 7 and Ap = 5+1+8 = 14
Product of areas (= "multiplication in real space"):
=> Ax * Ap = 7 * 14 = 98
Term-wise multiplication ("convolution in real space"):
termw[n] = {2⋅5, 4⋅1, 1⋅8} = {10, 4, 8}
=> Atermw = 10 + 4 + 8 = 22
Convolution ("polynomial multiplication in dual space"):
conv[n] = {5⋅2, 5⋅4+1⋅2, 5⋅1+1⋅4+8⋅2, 1⋅1+8⋅4, 8⋅1} = {10, 22, 25, 33, 8}
=> Aconv = 10 + 22 + 25 + 33 + 8 = 98

How is this all the same, yet not the same? Am I misinterpreting the concept of duality?
To make the confusion complete, the Fourier transformation is obviously not area-preserving as can be easily seen from these graphs:
Fourier Transforms
But it does seem to preserve the "multiplicativity of areas" when it comes to convolutions when transforming convolution integrals (areas) between real and dual space (i.e. convolution/deconvolution).
There must be some underlying concept that unifies all this clearly. I'm not a mathematician, but I've read that the mechanics behind convolution (crosscorrelation, autocorrelation) and Fourier transformation is intimately linked to the concept of products (Plancherel's theorem, square-integrable functions etc.). I remember from basic functional analysis the concept of complete orthonormal bases (ONBs) and that a Fourier series "is" a projection of functions onto an ONB of harmonic functions. And somehow, this translates into two different ways of multiplication (term-wise vs. polynomial). From this, convolution appears to be some kind of "generalized product" defined on functions and if we represent functions by harmonic series, Fourier transformation somehow transforms the "mechanics" of the multiplication (term-wise vs. polynomial).
I have a hunch to how Fourier transformation might serve to "simplify" a polynomial multiplication (which scales with the square of the number of monoms) into a term-wise multiplication (which scales linearly with the number of monoms): In a Fourier transformation, a function gets "projected" onto a complete ONB of harmonic functions (represented by complex exponential functions) and integrated. So any harmonic component in "disharmony" with an exponential's frequency will get averaged out. So for the polynomial multiplication, I imagine that all mixed terms are being averaged out leaving only monomic terms.
In other words, we are plugging prior information about the posited "harmonicity" of our functions (i.e. they can be represented by Fourier series) into our multiplicative operation in order to "save some work".
Of course, this is a very imprecise way of describing things - we are not losing any information by applying the Fourier transform as the original functions can be perfectly retrieved via the reverse transform, but somehow we have a representation of functions that lends itself "inherently" for doing multiplicative calculations (products). And it is the nature of this "inherent structure" that I'm asking about here.
I'm sorry if I cannot get any clearer here - but the fact that I cannot is precisely the issue I'm trying to clear up.
Answer: In time domain, when everything converges
$$\int_{-\infty}^\infty \int_{-\infty}^\infty f(t-y)g(y)dydt=\int_{-\infty}^\infty  f(t)dt\int_{-\infty}^\infty g(u)du$$
becomes in frequency domain
$$\widehat{f \ast g}(0)=(\hat{f}\hat{g})(0)=\hat{f}(0)\hat{g}(0)$$
It works the same way for the Fourier series and the discrete Fourier transform (with circular convolution for the latter), with polynomials (so that $P(e^{2\pi it})$ is a Fourier series) it gives nothing else than $$P Q(1)=P(1)Q(1)$$ where $P(1)$ is the sum of the coefficients and the coefficients of $PQ$ are the convolution of the coefficients.


MySQL no longer starting "An attempt was made to access a socket in a way forbidden by its access permissions." (Windows 10)

Question: I don't think this is another "some other process is using port 3306 rtfm" kinda question.
I have been running MySQL 8.0.x fine for a couple of months on Windows 10 for some local python development. As of this week it refuses to start (don't know the exact date of when it started, but logs say it was still running 30/10/2020).
2020-11-07T10:57:43.452460Z 0 [System] [MY-010910] [Server] C:\tools\mysql\current\bin\mysqld: Shutdown complete (mysqld 8.0.22)  MySQL Community Server - GPL.
2020-11-07T11:01:21.048896Z 0 [System] [MY-010116] [Server] C:\tools\mysql\current\bin\mysqld (mysqld 8.0.22) starting as process 3480
2020-11-07T11:01:21.071269Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2020-11-07T11:01:21.618118Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2020-11-07T11:01:22.095397Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Bind-address: '::' port: 33060
2020-11-07T11:01:22.174810Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2020-11-07T11:01:22.175307Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2020-11-07T11:01:22.177656Z 0 [ERROR] [MY-010262] [Server] Can't start server: Bind on TCP/IP port: An attempt was made to access a socket in a way forbidden by its access permissions.

At first I thought maybe the 3306 port was in used, but that was not the case. Did a reboot to be sure. Stopped Docker. Checked if the exception was still present in the windows firewall. All good.
Tried port 3307 just to see what happened. Disabled Windows Defender. Same result. So my feeling is this might be caused by some Windows Update or changed security setting.
netstat shows no process listening to port 3306:
netstat -ano | find /i "3306"
<no output>

I did google a lot, but couldn't really find anything beyond SELinux or Antivirus preventing stuff.
Any pointers. Probably Windows Defender / Firewall, but don't know what setting to adjust. Mysql exception rule is in place:

Valentijn
Answer: Found the issue. Even though I rebooted (turned off, turned on), my ethernet connection (via dell dock) was not active. So only wifi was active and apparently windows prevents services from listening to ports on that. Even though there's an exception present for public networks in the firewall.
Anyway, after disconnecting and reconnecting the ethernet cable it started working again.


TFS 2005 Wiki Template?

Question: Is there a Wiki plugin for TFS 2005, ie. SharePoint Services 2.0?
Answer: There is one here: http://www.neoworks.com/products/sharepoint/wikipoint/index.html
I do not know how good it is, but you can install a demo and try it out.
Answer: If you upgraded to TFS2008 then you could use a Sharepoint Services 3.0 portal which includes a basic Wiki feature.  There are many other reasons to upgrade to TFS2008 (less bugs, better speed, more features, great back-compat with VS2005 etc) but just thought I'd mention it.

TFS 2005 Wiki Template?


Is parlance a good replacement of 'area of interest'

Question: Is it a good idea to use the word 'parlance' to mean one's area of interest in a general way? Reliable sources suggest that the word be used only where the is area is more linguistic in nature. Has the word acquired at least a bit more figurative sense in the course of time?
Comment: Can you give an example of any sentence where the word seems to you to have the meaning "area of study|interest"? I am curious to know how this question arose in your mind.
Comment: It's a good idea to become familiar with English prefixes, suffixes, and roots.  The root of "parlance" is the French *parler* meaning "to speak".   Related words "parley", "parliament", "parlor".  It would be unusual to use it any context other than language.
Comment: Thanks for clarifying. I don't know why, but when I was going to write "it's not everyone's cup of tea" the other day, I thought "it's not everyone's parlance" is a better usage. The context had nothing to do with language, in fact. Thank you again.
Answer: No. Parlance does not in any way mean "area of interest."
"Parlance," used today, ordinary refers to the vocabulary and special definitions that are particular to a group. The group might indeed be defined by their area of interest. For example, you could say:

In gambling parlance, "call" means "to match someone's bet".

This said, your parlance could be the product of any number of identities. You might refer to "teenage parlance" or "milliary parlance." But parlance is a feature of those groups, not the groups themselves. You wouldn't say "my parlance is biology," for example.
Less commonly, "parlance" is synonymous with speech in general. You and I might decide that parlance was preferable to silence if we were waiting at a bus stop, for example. The word comes to English from French, so the classic connotation would be diplomatic speech. For example, an ideal leader could be said to be skilled in arms but prefer parlance.


Videos are not showing through filemanager which was downloaded through uc broswer

Question: I have Windows lumia 630 (8.1 update) updated UC browser & tube mate also, videos also downloads but thing is these videos are not searchable from file manager in either the Memory card or in phone. It acquires the space but can't able to find the place where it is situated/placed.
Comment: Is it just on the phone or you are unable to see the files after connecting to PC as well ?
Answer: The answer to this question lies in the fact that Windows Phone Apps uses "isolated storage" to store anything on your device. So, if you have downloaded anything from any app be it UC Browser or Youtube Downloader, you can't access it other than from within that App. You can access the file downloaded through the "downloaded files" section in UC browser. Let me know if any more concerns.
Thanks to this question:
How to find the videos downloaded with YouTube HD app
Comment: No. You are wrong. I downloaded a video in ucbrowser app and was successful in moving the video to different location. I moved the file to another location and was able to see in photos. I was able to access the file outside of ucbrowser
Comment: The answer is 3 month old. I didn't find any solution at that time. I am no longer using UC web. So, it would be great if you could just edit your answer and add the steps as to how you were able to access it.
Answer: Since Windows is a closed platform you can't view your downloaded files directly however you can do this in a few simple steps.

Open UC browser
Go to downloaded video
Tap an hold it
It will give you a pop-up menu
From this menu select "Export to SD card".

And nnow you are done. Now navigate to the file manager app and goto UCdownloads folder. Here you'll find your video. Now freely copy, move or share it.
Answer: If UC is downloaded to the sd card all the files are stored in
f:\WPSystem\AppData\local\Packages\Ucmobil~1\LocalState\Download
Here f:\ is your sd letter and ucmobil~1 is the only folder that begins with those letters in the packages folder
Good luck opening anything under there though. They all seem to require some kind of browser authentication to access or something. They wont open in anything else so if you deleted uc browser you'll have to beg the devs for some work around.... that they probably wont give.


Render frame from ISO file

Question: I have a video_file.mp4 and I know that the mdat atom contains H.264 frames. Also I have a H.264 codec lib in my project. So, am I right that if I put mdat raw data into my lib's byte * decode(byte * data, int timeMsec) method I'll get a decoded frame? Or I need additional operations?
Thanks!
Answer: There are two common H.264 bitstream packing formats.
1. Annex B
2. MP4.
For MP4 the packing mode is different and usually decoders prefer Annex B but not always.
MP4 is length prefixed and Annex B contains start codes. Some MP4 unwrappers will convert the bitstream to Annex B but not all.
Outside of the different packing formats – if your mp4 file contains any other streams – like – audio – your entire approach is not going work. The mdat box contains all streams interleaved.

Render frame from ISO file


How to change the workspace in android?

Question: My current workspace is in D drive I want to change my workspace and create a new workspace in C drive.How can I change the workspace in android?
Comment: There is no "workspace" in Android. I am assuming you are referring to Eclipse.
Comment: To accept an answer, click on the green checkmark next to an answer that you want to accept as the "best answer" to your question. That will reward people who help you and help you get better answers in the future.
Comment: After having switched the workspace (see NickT or JasCav answer) you may want to import existing code: File -> Import -> General -> Existing Projects into Workspace -> Next -> Browse to folder with project -> copy into workspace if necessary -> Finish
Answer: To change your workspace in Eclipse (as there is not a "workspace" for Android), open up Eclipse and select:

File > Switch Workspace > Other...

Then, select your new workspace location. You can copy settings from your current workspace if you want.
Answer: Create a folder anywhere you like using explorer.
Then from Eclipse menus do : File, Switch Workspace, Other - then browse to your newly created folder and click
Answer: I think that you should set the Android SDK for new workspace of eclipse again. You just need to click windows/preference/android and set SDK location, then click "apply" button.
Answer: Recently I moved my entire Eclipse installation directory but the workspace was still getting created in the older location only. And worst there was no option to select the Workspace directory in the Window->Options->Workspace menu.
To change the workspace location in Eclipse do this. Goto ECLIPSE_HOME\configuration.settings directory, edit the org.eclipse.ui.ide.prefs file and change the RECENT_WORKSPACES value to the desired location.
If you want that Eclipse prompts you to select workspace when you start it, change the SHOW_WORKSPACE_SELECTION_DIALOG value to true.
And you are done!
Answer: I strongly advice you to create your own start script. When you're on Windows something like
<code>@echo off
setlocal

rem set your Java settings here (JAVA_HOME and PATH) - setjava is a private script I use
rem call setjava 1.7 -arch x86_64

set ADT_HOME=D:\lang\android\adt-bundle
set ADT_EXEC=%ADT_HOME%\eclipse\eclipse.exe

set WORKSPACE_HOME=%~dp0

start "ADT" /MIN %ADT_EXEC% -data %WORKSPACE_HOME% -showlocation -clean -vmargs -Xmx2048M

endlocal
</code>

How to change the workspace in android?


Where are my apps?

Question: My handset was replaced under warranty and I was expecting my apps to sync to the new handset but when I check my apps in market none of them are listed.  Do I really have to manually find every single app and widget to download it separately?  Previously, such as after a factory reset, the apps would be listed and I could easily install them in one hit.  I am using the same Google account on the same type of Sony Ericcson Xperia Arc handset, albeit a new one.
Comment: The [web based market](https://market.android.com/account) seems to remember installation history longer than the phone version.
Comment: You could try going to `Settings -> Privacy` and ensuring **Automatic restore** is checked, though I don't know if it will help.  Google has only ever remembered my paid apps when I've done a reset, so I always do a backup.
Answer: If you go into the web version of the Play Store and then click on the link My Market Account at the top of the screen it shows you all the free and paid apps that you have downloaded since you opened your Android Google Account. From here you can also click the app name and then click the download button which then sends the download to your phone.
I've done this quite a few times when I have had to reinstall my phone
Hope this helps

Where are my apps?


how can we change the position of pop up?

Question: I am using google customer reviews script it showing a popup on my website corner bottom right but I want to change its position from right to left because my live chat is there but it's not working through CSS how to do it my code is

  window.renderBadge = function() {
    var ratingBadgeContainer = document.createElement("div");
    document.body.appendChild(ratingBadgeContainer);
    window.gapi.load('ratingbadge', function() {
      window.gapi.ratingbadge.render(ratingBadgeContainer, {"merchant_id": 7912975});
    });
  }
Answer: You can configure the position from the Merchant Center account. Login to your account go to Merchant Center programs. After go to Design > Layouts. Click on you block an you should have position.
You can see more details here.
Comment: it will be applicable for  all pages??
Comment: that changes the position of the review block. Technically it should be like that for all pages.


Is Gaussian Process just a Multivariate Gaussian Distribution?

Question: Besides the fact that The covariance is constructed using kernels. I am not sure if I am as clear on how MVN is much different from GP.
Answer: The multivariate Gaussian distribution is a distribution that describes the behaviour of a finite (or at least countable) random vector.  Contrarily, a Gaussian process is a stochastic process defined over a continuum of values (i.e., an uncountably large set of values).  Usually the process is defined over all real time inputs, so it is a process of the form $\{ X(t) | t \in \mathbb{R} \}$.  The Gaussian process is fully defined by a mean function and covariance function, which respectively describe the mean of the process at any point, and the covariance of the process at any two points.
Now, one of the central properties of the Gaussian process is that any finite vector of points has a multivariate Gaussian distribution with mean vector and variance matrix described by the mean function and covariance function of the process.  Specifically, for any time points $\mathbf{t}=(t_1,...,t_n)$ we have:
$$[X(t_1),...,X(t_n)] \sim \text{N}(\boldsymbol{\mu}(\mathbf{t}), \boldsymbol{\Sigma}(\mathbf{t})).$$
where $\boldsymbol{\mu}(\mathbf{t}) = [\mu(t_i)]_{i=1,...,n}$ is the mean vector composed of values of the mean function over these time points, and $\boldsymbol{\Sigma}(\mathbf{t}) = [\sigma(t_i, t_j)]_{i,j=1,...,n}$ is the variance matrix composed of values of the covariance function over pairs of time points.  The stochastic behaviour of the Gaussian process can be regarded as an extension of the multivariate Gaussian distribution to stochastic process defined on a continuum.
Comment: @ShaunHan: The Gaussian process is one where the joint distribution of any finite set of values is multivariate Gaussian/normal.  You can have a look in the link for further information.
Comment: So can I understand it as: Gaussian Process basically assumes a normal distrubution of functions?
Answer:
A Gaussian process is a generalization of the Gaussian probability distribution. Whereas a probability distribution describes random
variables which are scalars or vectors (for multivariate
distributions), a stochastic process governs the properties of
functions. Leaving mathematical sophistication aside, one can loosely
think of a function as a very long vector, each entry in the vector
specifying the function value f (x) at a particular input x. It
turns out, that although this idea is a little naı̈ve, it is
surprisingly close what we need. Indeed, the question of how we deal
computationally with these infinite dimensional objects has the most
pleasant resolution imaginable: if you ask only for the properties of
the function at a finite number of points, then inference in the
Gaussian process will give you the same answer if you ignore the
infinitely many other points, as if you would have taken them all into
account! And these answers are consistent with answers to any other
finite queries you may have. One of the main attractions of the
Gaussian process framework is precisely that it unites a sophisticated
and consistent view with computational tractability.

– C. E. Rasmussen & C. K. I. Williams, Gaussian Processes for Machine Learning, the MIT Press, 2006. (Emphasis is my own.)
Answer: I had the same question so I found the following on Stan user guide which I think has both a sort answer and a more detailed answer if you want to read further (well, by now you probably have nailed it but it might be interesting for other)


Why does my Honda Activa 4G handle vibrate a lot at low speed?

Question: I bought an Activa 4G in January 2018, the vibrations started after 120kms.
My 1st service was at 350kms(I did not use much). after the service the vibrations was not there. but after 650kms the vibrations again started. now I have completed 1000kms. Do I need to wait until my next service or any suggestions ?
Comment: Did you report the vibrations when you took it for the first service? When is your next service? If it is soon then report it then, if not take it in to get it looked at.
Answer: This is a rather general question. Without knowing anything about your riding style or habits, nor the conditions you ride in, or how you maintain your scooter, I am going to give you a couple things I think may be causing vibration in the handlebars.

Wheel balancing and alignment caused by hitting bumps/potholes
Poor running engine
Bad fuel causing #2

If the vibration is enough to concern you, or effect your ability to safely ride, then do not wait to have it serviced.


What to improvise over "fake" ii V I and succession of dominant chords

Question: I frequently see "incomplete" ii V I sequences in standards (like Satin Doll for example) where only the ii and the V are played and I'm always wondering what I can play there, since I find most of the stuff I play comes not sounding very convincing. Any idea what I can do besides taking usual ii V I patterns and getting rid of the last part ? Also do you guys have any way to deal with succession of dominant chords (dominant chords that are played as the fifth degree of another dominant chord) like let's say : | C-7 | F7 | Bb7 | ?
Comment: Those "fake" progressions are called _interpolated_ **ii-V** progressions. I'm not sure why what you are playing isn't convincing, but there are lots of ways to approach this. Learning patterns to play over progressions is okay to start, but won't get you very far, and I suspect the problem is that you are trying to shoehorn the patterns you know into place. The best thing to do would be to transcribe some melodies and solos from recordings that you admire. Then try to understand how those phrases work, and see if you can use that.
Comment: Note that lifting phrases from recordings is different than reading about "usual patterns." When you take these off of recordings by ear, you hear them in context. It is critical to spend time trying to understand how the phrases work; try to figure out where the chord tones are in the phrases. How does a phrase connect the chords of the progression? How are the notes accented in the recording? How does the phrase cross bar lines? You will learn a lot that you can use with this kind of work.
Comment: Perhaps you could be more specific about what you have tried and not tried. Off the top of my head, bebop scales would seem like an important tool explore for both of the situations you bring up.
Comment: Can you post a transcription of an unconvincing line?
Comment: You're all right I should have been more precise, I will post an example of a bad line as soon as i can get my hands on a guitar. In the mean time, do you hve any idea how to proceed with successions of dominant chords (like in doxy for instance) ? I usually play the corresponding mixolydian scale over each chord but i find it super boring, and I have difficulties to find convincing lines with diminished scales
Answer: For ii-V chords that don't resolve to I, the most straightforward scale to improvise on is the major key of the I. This is because the local key for those two chords is the tonic, whether or not you play the tonic chord next.
So in your example of Satin Doll, the first four measures would be:

dm7  G7 / dm7 G7 (improvise in local key of C major)
em7 A7 / em7 A7 (improvise in local key of D major)

DISCLAIMER: When I say the 'most straightforward' scale voice, that is understood to be a starting point and safe zone. If you only stick with those notes, it won't sound very inspired in the end.
The same a principle applies for a succession of dominant seven chords. Improvise using the major scale of the relative tonic.

C7 (F major scale)
F7 (Bb major scale)
Bb (Eb major scale)

The same disclaimer from above applies to. But even if you do just use major scales, there are some fun and creative ways to move from scale to scale as the chords progress underneath your improvisation line.
THAT BEING SAID: I hope I addressed the question, though in some senses what I said is just dropping the I chord and playing as usual which you stated that you are trying to avoid. But don't think about those ii-Vs as "fake" - they simply don't resolve to their tonic - or they don't resolve at all! But that's very much intentional and can serve an important harmonic purpose.
In the case of Satin Doll, the first ii-Vs build the expectation that you will land in C, but then you move up to the ii-V of D. Note, however, that this is also the iii-iv of C, so it plays naturally back to C anyway. (As in iii-vi ii-V I)
But a ii-V can also resolve really well to the tritone its tonic, which we see at the end of the A section. The seemingly random ii-V in Gb, Abmin7-Db7, actually resolves back to its tonic's tritone - C major. The key that the whole song has been building towards but avoiding until now! So simple, yet powerful and rich.


Unable to create shapefile in QGIS

Question: I am very new to QGIS and although I've been able to download the software and get aerial imagery using the plugins menu, I'm getting nowhere with creating a shapefile that I can use to draw a polygon on the aerial image. I've gone through the layer - create new shapefile procedure many times, but when prompted to save the shapefile on my C:drive, nothing happens.  I've tried using "add vector layer" then searching for the file I thought I'd saved, but there is nothing there.  Nor does the shapefile appear on the layers menu on the left of the project.  Where am I going wrong please?
Comment: Thanks Andre - saving elsewhere seems to have solved the problem.
Answer: Do you have full write permissions on C:\ ? Try alternatively your user directory.
A Windows- user name or folder name with non-ASCII-characters may spoil the saving as well.

Unable to create shapefile in QGIS


Database choice choice for Django project

Question: Django (http://djangoproject.com) framework currently supports the following databases: PostgreSQL, SQLite 3, MySQL 5 and Oracle. This question is not about the comparison of these databases, contrariwise I want to know details about their compatibility with Django and how one should choose an adequate database for a simple (but growing) project.
Answer: It depends. If you don't want to pay the (huge) premium for Oracle, your choice is between MySQL and PostgreSQL (SQLite is mostly meant for development, not production). PostgreSQL seems to be the choice of most Django core devs (Andrew Godwin went as far as putting "friends don't let friends use MySQL" into a DjangoCon talk). Nevertheless, MySQL is fully supported by Django and is used by many Django websites in production.
IMHO, PostgreSQL has two clear advantages over MySQL:

If you use GeoDjango. There's really no alternative to PostGIS. MySQL's GIS support is lackluster at best.
South. MySQL is not able to use transactions during schema migrations, which means if a South migration goes awry, you're hanging between two migrations without clear way forward or backward. PostgreSQL saves a lot of pain in such situations.
Comment: For the most complete answer! Thank you! ;)
Answer: All of the pluggable databases are supported, meaning, the the model/db-layer will abstract the db-specifics for you. As for performance, I'd suggest MySQL 5 or Postgresql. Oracle will definitely perform well, but might be more expensive in the long run. If you are just started your project, sqlite3 is your friend, simply because the it will be setup within seconds.
Handling parallel settings for development and production has been discussed in various blog posts, e.g. in this one:

http://ericholscher.com/blog/2011/jan/10/handling-django-settings-files/
Answer: The quick answer is it doesn't really matter but if I had to pick one, it would probably be PostgreSQL.
The original Django developers heavily recommended PostgreSQL in the early days.  PostgreSQL is arguably/technically a 'better' database then MySQL so if you've never used it before it might be worth investing some time to lean it.
Now-a-days though I'd say it's safe to assume that all the DB drivers work equally well.  So if you are more familiar with MySQL or Oracle there should be no problems using them instead.  I've only used Django with MySQL and haven't had any problems.