System Monitor : How to display net speed on panel

Question: I use system monitor with 16.04 in Unity. Currently, I get all the graphs and text indicator for Disk on top panel. I want to have net speed displayed instead of Disk. How can I do that ?
Answer: Xenial

Install indicator-netspeed from terminal
Run apt:indicator-netspeed from your browser's URL panel
Download 32-bit or 64-bit deb package from launchpad and install them via Software Center

Terminal install
sudo -i
add-apt-repository ppa:nilarimogard/webupd8
apt update && apt install indicator-netspeed

To start the indicator, run indicator-netspeed &

Bionic and up (with GNOME 3)
Gnome Extensions: Install
If you want to download the extension package manually, select your shell version and extension version.
GitHub: hedayaty/netspeed

Bionic with Unity panel
Terminal install
sudo -i
apt-add-repository ppa:fixnix/netspeed
apt update && apt install indicator-netspeed-unity

To start the indicator, run indicator-netspeed-unity &
Launchpad: Download
GitHub: ggleb/indicator-netspeed-unity
Comment: @blueray just type **apt:mate-netspeed** in your browser's URL panel
Comment: On bionic apt gives `Package netspeed is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source` so unfortunately this is not quite working...
Comment: how can I use it on Ubuntu Mate
Answer: In Ubuntu 18.04 simply open the Ubuntu software app and search for Netspeed. Click to install the app and it will be displayed on your upper status bar on the right side.
Comment: this does not work in 19.04
Answer: Unity (Ubuntu 17.04 and below)
Steps to see NetSpeed Indicator n Unity Desktop Ubuntu

Open the terminal.
Type the below codes in Terminal:
sudo apt-add-repository ppa:fixnix/netspeed
sudo apt-get update
sudo apt-get install indicator-netspeed-unity

Logout of the current session  & Login again for the changes to take effect.
Net speed indicator app will start automatically on top of the Unity Panel.
If you don't like to logout,  you can still start Netspeed Indicator Applet on Unity panel.
Open the terminal and type the below code to start the Netspeed indicator app
indicator-netspeed &

That's it. You can see the Upload & download Speed also by clicking on the Icon.
Answer: I use Netspeed for Unity for that with Lubuntu 18.04 LTS, and think this link to acquire Netspeed will be helpful; please note there's a version for 16.04 ('Xenial'), so you can disregard everything on that page but the second and third paragraphs, to wit:

sudo -i
add-apt-repository ppa:fixnix/netspeed
apt-get update
apt install indicator-netspeed-unity
Restart your PC/laptop.
Answer: GNOME Shell (Ubuntu 17.10+)
There are several GNOME extensions. The one with the indicator that I like the most is: system-monitor (AKA gnome-shell-system-monitor-applet)

Includes network speed and much more.
Alternatives

Vitals: Simple. Only numbers (without graphs).

Freon: Only numbers (without graphs).


Is it sensible to make all physics on GPU using transform feedback?

Question: I'm learning OpenGL and today I read something new to me. It's called transform feedback, and if I understand right, it can help to get information about vertex shader variables. And I read an example where a particle system was created, with collisions. After reading it I have a question: Is it sensible to make all physics like this, i.e. is there any kind of profit from this?
Answer: Physics done on the GPU are usually cosmetic effects. Particles are a good example, but hair and tall grass are similar. The GPU is very good at doing a massive number of calculations and since it also handles the drawing if these things it is a good match.
A GPU isn't very fast at communicating the results back to the CPU. This is why physics used in actual gameplay is done locally on the CPU: Collisions may affect both colliding objects or trigger other gameplay effects (e.g. points scored) so it makes more sense to handle that on the CPU.
Some physics effects may benefit from using the GPU to do some calculation offloading, but those are often handled by a specially designed physics core.
So in general, non-gameplay special effects that require some degree of physics are suited to run on the GPU.
Comment: it is a cascading effect. 2 frames before the game can react also means effect resulting from it may have a 2 frame delay and so on. In most games speed is everything; which is also the reason some effects are offloaded to the GPU.
Comment: Thank you for answer. But why I should send info back to CPU? Maybe it's dumb question, but I I'll ask. Why I can't allocate some memory from GPU to store data there?
Comment: If your game logic needs the info (for example an enemy is hit by a rock, the game needs to play a soundeffect) meaning the result should be sent back to the game. Now in desktop PC architecture GPU memory is separate from the mainboard memory. In console architecture there is usually some 'shared' memory space both the GPU and the CPU can access and is usually used for this type of communication. However in most situations these memory blocks are not shared.
Comment: @АйратНасыров Moving data around between CPU and GPU across system bus is inefficient; when you urgently need that data for other tasks so you can complete a frame of game logic in 1/60 sec, you haven't time to wait for such transfers to occur... generally speaking. Some games will run things 1-2 rendering frames behind the current logic tick, in order to give that data time to propagate back and forth (the same technique is also sometimes used in networking).

If a particle has a gameplay effect like burning a character in the current frame, you need it _now_, not 2 frames from now.
Comment: Thank you. Is 2 frames are really so important? I think no-one can feel it) I mean it's 2/60 sec!!!


How to characterize surface features in proteins?

Question: When looking at the structure of protein domains I notice many of them show a cleft-like structure in the same location (when aligned to each other). What is a recommended way of characterizing these clefts? Maybe some curvature measure? I want then to relate them with electrostatic potential so that I can correlate these clefts with some charge or electrostatic potential. Here I'm attaching an example of what I mean:

Comment: @IvanP You are very welcome to answer your own question, as we currently don't have very many users, and many of us don't know much about the modeling of proteins. We are also trying to reach [90% answered here](https://area51.stackexchange.com/proposals/122958/materials-modeling). The papers you mention in your comment, might even be helpful to be in the actual question (it's up to you).
Comment: It looks like a rhino beetle horn
Comment: I just found this review of some methods to find pockets for interaction with ligands. It somehows explain methods that can be used to characterize what I need but it is a bit old: https://onlinelibrary.wiley.com/doi/full/10.1002/jmr.984 . That led me to https://www.nature.com/articles/s41401-019-0228-6 ... seem like papers worth studying, maybe after that I can answer my own question? :)
Answer: Normally, if various proteins have the "same" cavities/clefts, this means that they are part of the same family and the amino acids that form the cavity are conserved.
I really don't think that the electronic properties (charges and electrostatic potential surface) are directly related to the geometrical shape. Instead, they are related to the residues that are in the cavities, the protein protonation state, etc.
Normally, the interest in protein cavities/clefs is related to their activity. So, we look for small molecules that bind to proteins in their cavities and change the protein state.
Servers like CavityPlus, for example, are focused on cavity detection and functional analysis whereas servers like CASTp, are specialized in topological analysis of protein cavities.
Comment: Yes, they are the domains of the same protein. And I agree, charge is not related to geometrical shape, but what's interesting is that for this case it may be, or at least I want to check if it's the case. That's why I'm looking for tools that can help with this. Thanks for the answer!
Comment: You have another issue with the charges: they depend on how they are calculated (they are associated with each forcefields -easy to work with- or you have to calculated -hard work due to the system size-)
Comment: Yes. But we can consider that the charge problem is already solved. In the image there blue is positive and red is negative electrostatic potential. That was solved using a Poisson-Boltzmann solver. I also have the charge distribution using another tool.


How Apple.com set Apple Touch Icon?

Question: Apple Touch Icon is a icon used in Safari 8 favourite new page on OS X,or web clip in Home screen on iOS.
https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html
there is two way to set it,one is using rel="shortcut icon",another is using rel="apple-touch-icon" like http://apple.stackexchange.com do.So I can find icon URL http://cdn.sstatic.net/apple/img/apple-touch-icon.png?v=2a2c3caaec7f
However apple.com doesn't use those two method.How can I find apple.com's apple touch icon URL?
Answer: Is it not just http://www.apple.com/apple-touch-icon.png?
From the iOS Developer Library article you pointed to above...

To specify an icon for the entire website (every page on the website), place an icon file in PNG format in the root document folder called apple-touch-icon.png
Comment: But I add to my website www.cuthead.tk/apple-touch-icon.png,add www.cuthead.tk to my favourite,why I still not see the icon show out?
Comment: It works for me when I try to create a bookmark (favorite is the term used by Internet Explorer) or web clip in iOS 8 Safari on an iPhone 5S.
Answer: I found Safari use mobile UA to get mobile HTML to get mobile Apple Touch Icon to set Desktop Safari favorite bar.

How Apple.com set Apple Touch Icon?


What does status R mean regarding trail permits on the Mt Whitney lottery calendar?

Question: I lost out on the Mt Whitney lottery--dates I was looking for now say R--does that mean I am out of luck or will some slots be available later, like in the April 1 access date?
Answer: Yes, it means that you are out of luck for that day.

After the Mt Whitney Lottery, any remaining dates may be reserved on the website www.recreation.gov beginning at 10:00am Eastern Time on April 1st. When searching for an available date, the letter "R" on the reservation calendar indicates that date is full. Reductions in group size and canceled space will be released for web reservations at a random time within 24 hours of cancelation. A reservation is not final until you have successfully completed checking out the shopping cart and paid reservation fees in full.

Source
The full legend of what the letters stand for on the calander is,

A: Available for online reservation (click to book entry date)
a: Available for online reservation with earlier arrival date
L: Accepting Lottery Application (click to apply for the lottery)
W: Available at the Facility
R: Reserved
C: Closed
X: Not available
N: Not available

Source


Accurate and Concise Translation of Dhamma Qualities

Question: The common stanza describing qualities of dhamma goes as "Swakkatho bhagawatho dhammo sandittiko..." which describes six of them. I am looking for an accurate and concise translation of this from someone good in both Pali and English; and of course Buddhism
Comment: This sounds & doesn't sound like what you are looking for: Properties of Dhamma:
1. Steadfastness of the Dhamma
2. The orderliness of the Dhamma
3. All processes are inconstant, suffering, and all phenomena are not-self
(from Iti. 51) From "The complete Book of the Buddha's Lists
Answer: There's one here -- Dhammānussati:

Svākkhāto bhagavatā dhammo: sandiṭṭhiko akāliko ehipassiko opaneyyiko paccattaṃ veditabbo viññūhī ti.

The Dhamma is well declared by the Bhagavā: visible here and now, immediate, inviting to come and see, effective, to be individually ascertained by the wise.

If you use a mouse to hover over one of the coloured words (of English or Pali) there's a popup containing a little definition of the Pali:
Answer: "(1)Svakhato Bhagavata Dhammo, (2)Sanditthiko, (3)Akaliko,(4)Ehipassiko, (5)Opanayiko, (6)Paccattam Veditabbo Vennuhi ti."
"(1)Well expounded is the Dhamma of the Exalted One, (2)visible here and  now, (3)immediately  effective, (4)inviting  one  to  come  and see, (5)leading onwards, (6)to be realized by the wise each for himself."
Source
PDF Pg 16, The definitions are further explained in the book.


How do I ensure the substitution happens after I take the first derivative before taking my second derivative

Question: The title may be a little confusing so let me explain what I mean:
I am using lagrange brackets to produce some equations of motion for orbital mechanics, where the motion is split between oscillating and mean elements. I'm doing the same thing as brouwer theory if you're familiar with that.
Basically motion is decomposed into a mean element which varies linearly in time and a quickly var oscillating portion.
Anyways, to make the oscillating state elements I need to take derivatives of a generating function. I also further would like to take the derivative of the oscillating elements with respect to the mean elements for least squares routines to estimate mean elements.
So I have been able to successfully produce the oscillating elements, but when attempting to take the derivative of those I run into a problem.
To get the oscillating elements I have to take the lagrange brackets of my elements  with the generaging function ie <ei,W>
Where ei are the state vector I am using, W is the generating function and l, g, h,L,G,H are a seperate set of state variables other than those in ei called delaunay variables. So far so good
Next I want to use least squares to find the mean variables. To do so as stated above I need the derivative of the oscilating to mean elements. To do this I need to define the l, g, h, L, G, and H in terms of my state variables, and then take the derivative.
Unfortunately since I'm using DelaySet, mathematica attempts to take the derivatives all at once at the end, which cause the derivative to fail, as it cannot take the derivative with respect to l, g, h, L, G, and H as they are now functions of my variables ei.
How do I fix this without hand transcription? I have tried using evaluate around the derivatives with respect to l, g, h, L, G, and H, and using set rather than delay set (as in = instead of :=). I have not been able to get the desired behavior
Here is a portion of the code cut out to illustrate whats not working:
<code>L[n_, \[Mu]_] := Sqrt[\[Mu]*a[n, \[Mu]]];

e[h_, k_] := Sqrt[h^2 + k^2];

G[n_, \[Mu]_, h_, k_] := L[n, \[Mu]]*(1 - e[h, k]^2)^(1/2);

i[p_, q_] := 2*ArcTan[p^2 + q^2];
H [n_, \[Mu]_, h_, k_, p_, q_] := G[n, \[Mu], h, k]*Cos[i[p, q]]
xsi[h_, k_] := ArcTan[h/k];
l[h_, k_, lm_] := lm - xsi[h, k];
g[q_, p_] := ArcTan[p/q];

hDel[h_, k_, q_, p_] := Simplify[xsi[h, k] - g[p, q]]

W1lp1[l1_, g1_, hDel1_, L1_, G1_, H1_, n_, h_, k_, q_, p_,
 lm_] := -(1/(32*G1^3))*(1 - G1^2/L1^2)*(1 - 5*H1^2/G1^2)^-1*(1 -
   16*H1^2/G1^2 + 15*H1^4/G1^4)*Sin[2*g1]
Mean to Oscillating Transformation Long period  portion

nW1lp1[l1_, g1_, hDel1_, L1_, G1_, H1_, n_, h_, k_, q_, p_, lm_,
  mu_] := -dndL[n, mu]*
   D[W1lp1 [l1, g1, hDel1, L1, G1, H1, n, h, k, q, p, lm], l1] -
  dndG[n, mu, k, h]*
   D[W1lp1[l1, g1, hDel1, L1, G1, H1, n, h, k, q, p, lm], g1] -
  dndH [n, mu, h, k, p, q]*
   D[W1lp1 [l1, g1, hDel1, L1, G1, H1, n, h, k, q, p, lm], hDel1];

DnOscDnMeanlp1[n_, h_, k_, q_, p_, lm_, mu_, J2_, rE_] :=
 J2*rE^2*D[
   nW1lp1[l[h, k, lm], g[q, p], hDel[h, k, q, p], L[n, mu],
    G[n, mu, h, k], H[n, mu, h, k, p, q], n, h, k, q, p, lm, mu, J2,
    rE], n];
</code>
The problem is with the last function as I can get the ones above to work. I've also posted the full code in a comment below
Edit: I believe a better way to ask this is the following: How do I ensure the substitution of the delaunay variables happens after I take the first derivative for the lagrange brackets and then take the second derivative with respect to my orbital elements.
Edit 2: I've continued to update the code on github with my latest attempt
Edit 3: As some of yall have upvoted the response to post the code I decided to put it into the main area as well:
https://github.com/pjdog/mathematicaStuff/blob/main/Just%20the%20code%20copied%20as%20github%20doesnt%20display%20mathematica%20well
.
Comment: Please share your code. We can't help you debug code we can't see.
Comment: @MarcoB I just uploaded the code to github in this folder: https://github.com/pjdog/mathematicaStuff
Comment: I hope that an okay way to share the code, as I don't want to copy and paste a whole block
Answer: Okay so I figured it out. For the derivative to work I need ot use set rather than set delay, while also being very careful about it. That is I use set rather than set delay (= vs :=) before the final derivative. I will be deleting my mathematica code from github but if you in the future somehow come across this and need to know how to do this, DM me! Thank you all
Comment: I changed my mind and actually updated the code on the github! I hope this helps future people!
Comment: Can you please update this answer with the modified code that works? This way, along with you having posted the original code, is better for future users to be able to solve this problem too :)


Manual failover of AAG in SQL Server 2012

Question: Just a question regarding manual failovers.  Does it matter if we use SSMS to perform the failover vs going to the Failover Cluster Manager and move the role to the secondary node?  Is there a preferred method or either one is fine to do?
Answer: Do not use Failover Cluster Manager for your failovers. It can cause problems.

Do not use the Failover Cluster Manager to move availability groups to
  different nodes or to fail over availability groups. The Failover
  Cluster Manager is not aware of the synchronization status of the
  availability replicas, and doing so can lead to extended downtime. You
  must use Transact-SQL or SQL Server Management Studio.
Answer: Complimenting to Tara's answer ... You should tsql / powershell for availablity group failover.
T-SQL : ALTER AVAILABILITY GROUP MyAg FAILOVER;
PowerShell : Switch-SqlAvailabilityGroup
You should check is_failover_ready in sys.dm_hadr_database_replica_cluster_states dmv to see if the replica is ready for failover and there wont be any data loss.


Is there any way to use a touch screen monitor to CONTROL an Android tablet through USB?

Question: I have a Coby MID7065 Android tablet that I want to connect to a 4 wire capacitive touch screen monitor via USB. I want to be able to control my tablet via the touch screen monitor. I need to know if there is a way to do this, or if drivers that must be written for the Android OS to make this work or where I can get this information.
Comment: Do you have a link / picture of "4 wire capacitive touch screen monitor via USB", with the device and wires? I can't imagine what that looks like. Interesting problem / question though.
Comment: No i don't. A 4 wire capacitive touch screen is a type of touch screen. There is also a 4 wire resistance touch, projection capacitive, and infrared as well. The last two people are most familiar with because tablets and smart phones use these technologies for their touch screens which also allows for multi touch applications.
Answer: As far as I know, no Android devices ship with drivers for a USB touchscreen monitor. To make this work, you'd have to find or write drivers for Android, and they'd probably be specific to the type of monitor.
In the first instance you could approach the monitor manufacturer and see if they know of a driver for Android, or are willing to give you the datasheets you'd need to write one.
Comment: There's no need to comment to say thank-you. If the answer helped you, accept it using the green tick/check mark on the left. That's our way of saying thank-you. You get some reputation for doing this too!


Prevent https on Openshift

Question: I want to cancel https on Openshift, I've just known that the server returns a header Strict-Transport-Security which forces https, is there anyway that I can force http when using Openshift because i'm getting some issues with chrome, it is not loading some resources from http sources when using https
Answer: The bug has been documented here: https://bugzilla.redhat.com/show_bug.cgi?id=908417 (login required)
This should be fixed in the next update to OpenShift, and when using Google Chrome version 26 or later.
Comment: This bug has been fixed, the server no longer forces https

Prevent https on Openshift


How would civilized beings build nests?

Question: The beings in question are human-sized that instinctively build nests when they are ready to have kids. The nests are similar to a drey but with the opening on top, like a bird's nest, and are roughly the size of a bed. Naturally, they are used as cribs once the babies are born, and are used while trying to conceive beforehand. They are naturally built in sheltered places on the ground (under a tree, for example). They can also use and create technology like humans. Would their use of technology affect their nests, and if so how would the nests be different?
Comment: With power tools, of course!  :-)
Comment: It could be that nest building is still really important in social contexts, especially romantic contexts. We humans have quite a few traditions (that vary from culture to culture) which we do not abandon, despite some being not very "smart" (i.e. useful) - but you can still enjoy them ;-).
Comment: Could they be "bird people" (humanoid birds)? Or it could be just art/aesthetics like in [this article](https://www.treehugger.com/human-sized-bird-nests-jayson-fann-4853395).
Comment: @0.. It's an instinctual thing
Comment: i assume their biology is just like human right?
Answer: As intelligent beings, they will, like us, have long since abandoned (or, if you will, supressed or modified) their instincts for civilized behaviour. They will buy their nests at Ikea.
Comment: And they'll also have entire sections of media dedicated to nests such as Extraordinary Nests, Nest Brothers, Extreme Makeover: Nest Edition, the famous magazine Nesting Digest, plus plenty of social media accounts dedicated to the subject
Comment: Still, nest building should be a #1 crafting hobby among them ;)
Answer: Instinctual behavior is bad for smart.  Birds that are precocial and know to do things as soon as they are hatched are dumber than those that are born helpless.
Your beings would have evolved a culture of nest building, which is very conservative because your bright idea might kill your baby.  Still, it will develop with two main pressures:  less labor, however you measure it, and works better.
Permanent structures are build once, use many times, which allows you to,preserve good ideas and not pay/build again, as long as basic sanitation measure are feasible.  Furthermore, sheltered locations can be built and not just looked for.
Probably as soon as specialists are feasible, there will be nest builders and nest cleaners.  In the early days, this might even be a magical or religious role, to protect the young.

How would civilized beings build nests?


Why is axiomatic system needed in propositional logic?

Question: I am trying to learn  propositional logic. I have read that axiomatic system is defined since there are some problems which can not be solved using truth tables. I have found such a problem in predicate logic when we use quantifiers. There we should use axioms to derive a formula which contains quantifier, since we can't construct truth table of that formula. But I am interested why we need axiomatic system in propositional logic? We can check if a formula is tautology using its truth table.
Answer: As you said we can check if a formula is a tautology just looking at it's truth table, anyway studying logical system (i.e. a system with has axioms and inference rules) also for propositional logic can be interesting for different reason:

first of all there's the didactic reason: it's a simple deductive system, indeed it can be seen as just a fragment of the system for first order logic, so it helps to familiarize with deductive systems;
a second reason it's complexity: sometimes proving the logic validity of a formula through such deductive system can be easier then proving it via truth tables, which involve calculate the truth values of a formula for all possible valuation of the variables which can become easy a troublesome for formula with huge number of variables, while in many cases writing a proof can be much easier involving just few application of inference rules.

Probably there other reasons too that I'm not remembering right now, but I reserve to myself the right to add them later. :)
Answer: (a) Giorgio Mossa is right. Two reasons for considering deductive systems for standard truth-functional propositional logic are

they can be used as toy examples, as warm-up exercises to the more serious business of considering proof-systems for quantificational,
  modal, and other logics,
they can (in some cases) deliver proofs-of-classical-validity more efficiently than hacking through a truth-table.

(b) But of course, it all depends which deductive system you look at. The OP mentions axiomatic systems. Well, here's one perfectly good axiomatic system for propositional logic (not just a trick but actually used in some books for the propositional fragment of quantification theory):

For any truth-functional tautology $\varphi$, $\varphi$ is an axiom.

And for pure propositional logic you don't need any additional rule of inference, so all proofs in the axiomatic system are one line! That's just fine, since it is recursively decidable what's an axiom, which makes it a kosher axiomatic logic -- and one which is trivially sound and complete for theorems of classical propositional logic!
(c) But let's set aside such trivialising examples, though they remind us that different deductive systems will have different virtues! And indeed now set aside axiomatic systems in the sense of Frege-Hilbert systems more generally (they usually don't have virtue (2) anyway). Let's concentrate on Natural Deduction proof-systems of one style or another. Now there is an additional reason for being interested in these:

3 Arguably, the ND introduction and elimination rules for connectives fix their sense.

Arguably, what we grasp in pre-formally understanding logical operators is their inferential role, is how we can use them in argument (in a Wittgensteinian slogan, to ask for the meaning [of logical operators] is use for their [inferential] use). Then, in the propositional logic case, a Natural Deduction system can be thought of aiming to directly encapsulate the meaning of the connectives by laying down the inferential rules governing their use, which determine their meaning.
On this sort of view, which we owe to Gentzen, there's a kind of priority to the deduction rules in an ND system -- and it will be a non-trivial discovery that the resulting system is sound and complete with respect to a Boolean truth-functional interpretation.
(d) Or that will be a discovery if, indeed, we accept the "classical" ND rules. But of course there are issues about that. From Gentzen's perspective, there is arguably something anomalous about the classical negation rules (so-called failures in "harmony"). And we can worry too about the classical structural rules that allow unrestricted chaining of proofs in a way that gives us fallacies(?) of irrelevance. But the details don't matter for now, just the following general point:

4 In considering ND systems for classical propositional logic, we can also -- in a smooth and natural way -- investigate neighbouring non-classical logics that arguably avoid some shortcomings of the classical paradigm.
Comment: Your trivial system needs a bit of work to be as strong as standard proposition logic: at the moment $p\vee p \vdash p$ is false, for example.
Comment: @ChrisEagle Yes, thanks, I should have explicitly said (and now do say!) it's sound and complete for *theorems* not *consequences*. [There's an obvious correlate which is sound and complete for consequence for *finite* sets of premisses, and we could then add a definition of consequence for infinite sets of premisses which builds in compactness.]
Answer: Another important use of deductive systems is in proving compactness results. As soon as you have a complete sound deductive system in which proofs are finite, you have a compactness theorem: if a formula $\phi$ follows from some infinite set of premises, then in fact it follows from some finite subset.
Compactness of propositional logic is a much weaker tool than compactness of predicate logic, but it serves as a toy example, and isn't entirely useless in its one right: it is still strong enough, for example, to express many of the compactness arguments used in combinatorics, in which one deduces an infinitary result from its finitary equivalents. For instance, the four-colour theorem for infinite planar graphs can be proved from the finite case in this way.
Of course, with this perspective, you don't really care what proof system you're using, as long as it's complete. This is one reason why unwieldy Hilbert-style systems are used: it's a frustrating amount of work to actually prove any worthwhile result within them, but it's comparatively easy to prove metalogical results like completeness.
Comment: We *can* prove compactness theorems by going via soundness/completeness results for a finitary proof systems. But *should* we? :-) Compactness is a purely semantic property and so some will say it "ought"(!?) to be proved, as it can be, by a purely semantic argument ...
Answer: Truth tables are local to the logical semantics used.  For example, if you use a truth table for a two-valued logical semantics, it shows that the well-formed formula is always true with that two-valued semantics.
On the other hand, axiomatic systems are not local to the logical semantics used.  If you prove something, you've shown that it doesn't hold only for those semantics, but any semantics where the axioms get satisfied.  You've shown that the formula holds for several models.  This is comparable to how if you use the axioms of Boolean algebra to prove an equation, you've shown more than if you had just used the 0-1 Boolean algebra, and didn't have the result that the 0-1 Boolean algebra can get used to show equations true for larger algebras.
So, if the motivation for a logic in part consists to address more than one possible semantics, an axiomatic system can be preferable.
Additionally, if you study non-classical logic and have seen some formal proofs (or can tell a formal proof would be simple enough to produce) in classical logic, you can reuse those proofs for the non-classical logic where all of the axioms and rules of inference in the classical logic proof also hold in the nonclassical logic.  Thus, if the motivation for studying classical logic in part lies in being in a better position to study nonclassical logic, axiomatic systems can be preferable to truth tables.
For example, if you have take a usual proof of CCpCqrCCpqCpr in classical logic, you might find that it only uses the axioms CpCqp and CCpCqrCCpqCpr.  But, that proof implies that CCpCqrCCpqCpr is also a theorem in intuitionist logic, minimal logic, and the pure implicaional calculus.


How to share my WAMP installation between two XP and Win7 on my pc?

Question: I have a dual boot system, meaning, I have both WinXP and Win7 installed on my system. I have installed WAMP server for testing and development purposes on my WinXP, and now I want to use the same installation from Win7 as well, so that I can work on same project no matter which OS I am currently using. Is this doable?
Answer: I think you need install your alter OS on a virtual machine to use WAMP share setting. after run both win 7 on your system and win XP on virtual machine that installed on win 7 , you can run the WAMP SERVER as a real server for all of your OS.
Answer: I would install WAMP on both OSs but move your website source code to something like Dropbox. Then your changes will be synced across both OSs.


Unknown Symbol : Slash with two dots

Question: I have checked through music notation lists and have asked a number of musicians but nobody knows what this symbol is actually supposed to mean.
Comment: handy reference for the next "notation question" :  http://www.dolmetsch.com/musicalsymbols.htm
Answer: It's a simile. There are a few different types of similes and  this one means "play the last notated measure again". So in this piece you will end up playing the measure before the simile marks 3 times, then play the next notated measure.
It's pretty much a very shorthand way of saying "Play what you just played again".
Comment: Yes. So after 13 you would play measure 13 again twice since there are two single measure simile marks.
Comment: Yes.   If it has two slashes,  you play the previous 2 measures.
Comment: @JacobSwanson so you could write the whole cello part of Pachelbels canon in D with 2 measures and then the 2-slash simile repeated again and again, plus one end note? I'd never thought of that because I didn't know the 2-slash variant.
Comment: If you only played the 2 measures for the entire piece(except for the end),  I don't see why you couldn't.
Answer: It is short-hand for "play this measure the same way you played the previous measure". Sometimes it is called the "repeat bar" symbol. It is frequently found, for instance, in fake-book charts and in notation for the "rhythm section" in jazz, meaning percussion, bass, piano and guitar (with guitar, particularly for indicating that you are to repeat a certain strumming pattern for chords). Sometimes you find a numeral over the symbol, meaning "play the same one-bar pattern for 2 measures", or 3 measures, or 4, etc.
Answer: Repeating what everyone else said: that symbol means repeat the last bar. Periodically, there are also ones that mean repeat the last two (or however many) bars. I don't remember off the top of my head what made that one look different, it was very similar, but I believe there was a number printed that helped with that conclusion.
They can't just put in normal repeat signs because the melody does not repeat, and that would mess up measure numbers, but it saves ink and your effort once you're used to it, to just say "repeat" like that.

Unknown Symbol : Slash with two dots


How important is modularization of software projects

Question: Modularization is obviously important in software projects, but I want to know people's opinions on how important and for what reasons it is important. I've obviously got my own ideas since I'm asking this, but think of it like a "common brainstorm" of the reasons one should modularize one's software projects...
Comment: should be community wiki
Answer: We humans are limited when it comes to grasping complex problems all at once.  However, we are gifted in the ability to decompose a complex problem into a (possibly very large) number of individual problems that are not too complex in order to tackle the big problem.
This is fundamentally what drives answers like "reuse", "separation of concerns", "easier maintenance".
All of these reasons are true whether it is one person breaking down a complex problem to tackle piece-by-piece, or if it is a team of people breaking it down to distribute the complexity.
Comment: Nice explanation of "Divide and Conquer" ... :) +1
Comment: To me, this is the primary importance of modularization (and encapsulation, for that matter).  It's the ability to reduce the working set necessary to make changes by scoping in on a narrow portion of the solution, without having to think (too much) about the larger system.  With large systems, I know that *I'm* not smart enough to keep it all in my head!
Answer: I think one of the main aspects is reuse. When you build things modularly, there's hardly things like: "Oh, I've already done this before, but to use it, I'll also have to get this and this functionality, which has absolutely nothing to do with my application".
Also, it is easier to understand. I can't keep tons of things in my mind at the same time. When the code is modular, there's easier to establish an "area" of things that makes sense in themselves. And once this area tends to be small, I can understand it as whole rather than pieces of it.
Finally, when things are smaller, it is easier to test and maintain. Also, your tests indicate faster where the error is, once they will test only a small part of the application.
Answer: My main reasons for putting code into different modules:

Separation of concerns: I feel that it is easier to limit the knowledge about the internals of classes on different levels or with different tasks if they are organized into separate modules. It simply feels more "dirty" to rely on internals if they are well hidden.
Easier to maintain smaller components: I usually find the development environment to be more responsive if I am working on a project with fewer code files, than if the project contains hundreds and hundreds of files.
Prevention of namespace clashes: When properly modularised, e.g. using namespaces in Java, you can have the same function name for the same functionality without having to worry that the printout() function in the Foo component will clash with the printout() function in the Bar component.
Separation of security concerns: It is easier to minimise the potential damage when one component steps on the toes of another component. Depending on the technology being used you can limit where each module can play in memory.
Answer: Modularization and decoupling are important for many reasons, some are:

Reuse: It is much easier to reuse software modules that are dedicated to specific purposes
Managing Complexity: Working on decoupled modules (writing code, debugging, maintaining etc) keeps your focus on a certain domain problem without being distracted by other aspects of the application or the software system.
Answer: It can also be viewed as a basic activity of Application Architecture which:

takes some business and functional specification
and group the major functions into applications while identifying non-functional modules and pure technical transversal module

That is why a "financial portfolio computation" will actually be divided into:

a computation module
a dispatcher module (because a portfolio is too big to be computed on one server)
a launcher module (to pilot all the computations)
a GUI (to see what is actually going on)

Plus several transversal ones:

KPI logging
Exception management

To treat that kind of functional requirement as one big monolithic module would force the development to implement all the sub-routines in sequence as a all.
Whereas with a clear application architecture, you can begin to work on the more general and transversal modules while still refining the other more business-oriented modules.
It also forces you to define more interfaces, and to analyze the inter-communications issues your different modules will have to solve (direct n-to-n typology? Bus?, ...)


Names based on real world culture

Question: I'm trying to name the gods of the pantheon of my world with names inspired by real world cultures and civilizations. My concern is that I come up with names that aren't culturally insensitive; particularly towards middle eastern and native american cultures. Are there any resources that I can consult?
Comment: Have you tried googling names to see if they happen to be offensive?
Comment: Beware that quite often gods have names which are *specific* to the gods, and never used for mortals. No Greek woman in the Antiquity would be called Athena, or Hera, or Artemis. Roman goddesses had personal names, such as Minerva or Venus, whereas Roman women did not -- they used feminine forms of their father's clan or family name. Our One True God has a Jewish name; Muslims never mention His name, but rather always referred to Him as God, of The Merciful, The All-Powerful etc. Some cultures prefer to use foreign names; e.g., many European cultures tend to use Hebrew, Greek or Slavic names.
Comment: You might actually find [this](https://azgaar.github.io/Fantasy-Map-Generator/) useful?
Comment: https://www.samcodes.co.uk/project/markov-namegen/ - try a procedural name generator
Answer: Each language has a unique phonology (the sounds that correspond to letters) either in their Latin script or in the romanized form of their language. Look up the Latin script phonology of the language and try to come up with a name that fits the phonology. Don't use the names of real gods/goddesses (as that will essentially guarantee an offensive name). This should work.
Comment: I usually do this (pick a language with a suitable phonology) and then combine existing names from that language. Like, if I were going for Amharic, a city name would be Adsuba (Addis Abbeba + Aksum)
Answer: If your looking for deities in the context of mythologies, [ https://pantheon.org/ ]
might be useful.
If your looking for a list of deities from a bunch of different cultures with short descriptions, Encyclopedia of Gods might be useful [https://www.amazon.com/Encyclopedia-Gods-Over-Deities-World/dp/0816029091].

Names based on real world culture


Django, How to clear the previous data model thoroughly?

Question: I'm viewing my admin site, but in the Add Groups page, I can still see the available permissions that I have deleted before. and in my models.py I haven't configured any of these table yet.

Does this mean I didn't clear my database thoroughly? Is there any way to delete all of these, just leave the permissions I have in this list?
Thank you!

Update:
I dropped my database created a new one, and re-built my data model. I can't view my previous group now :)
Answer: I dropped my database and my previous database user (Don't know if a new user is necessary), and created a new one. Then all my previous groups in this list disappeared. :)


Word or phrase to mean 'perfectly accurate?'

Question: Is there a word or phrase in English that means accurate to an infinite level of precision? For example, the measurement of a length that is 'perfectly accurate' records the length down to its final decimal place.
Comment: Just for benefit of people seeking by title - the phrase describing perfectly accurate to be used in common-day English, as opposed to (requested) "scientific accuracy" is **Spot-on**.
Answer: In a mathematical context, the word would be exact. An exact calculation always gives the mathematically expected result. The opposite is approximate: an approximate calculation gives a result that is close to the exact result, but not identical. For example, the circumference of a circle of radius 1 is exactly 2π, which is approximately 6.283. These words are also used in computer contexts: for example, financial calculations are usually done with exact arithmetic (using integers or fixed-point decimal numbers, with well-defined rounding rules), whereas physical calculations are usually done with inexact or approximate arithmetic (using floating-point numbers, with rounding rules that are intended to maximize the precision of the result but not always to be perfectly reproducible).
Strictly speaking, a physical measurement cannot be exact (the length of a stick has no "final decimal place"). However you can still use the word exact to mean that the precision of the measurement is so great that the uncertainty about the measured quantity will never matter. You can also use perfectly accurate in this context (again, meaning so accurate that any inaccuracy is irrelevant).
Comment: @Giles: I disagree - and so does OED, which defines ***precisely:** With precise or **exact** correspondence, in every detail; with **complete accuracy***. I think you're overly influenced by mathematical contexts where "precision" is a "variable" attribute relating to ***how*** accurate a value is.
Comment: "Precise" can be another option.
Comment: @Mistu4u No, *precise* is a relative term, not an absolute term. A measurement to 1% accuracy is *more precise* than a measurement to 10% accuracy. A measurement that is said to be *precise* may not be perfectly accurate, no more than a *tall* person is infinitely high.
Comment: @Gilles, that's only because of the dilution of the language. Apparently "precise" has lost its precision. http://www.thefreedictionary.com/precise  _2.  Exact, as in performance, execution, or amount; accurate or correct: a precise measurement; a precise instrument._
Comment: @TecBrat True, there are contexts where the two words can be used interchangeably, but not all of them. A *precise* clock might stay accurate for months; a *very precise* clock might stay accurate for a lifetime. (Notice the qualifier *very*? You can't use it with *exact*, except for stylistic effect.) An *exact* clock would always tell the time. As far as I know, *precise* was never specifically about exactness, so it isn't a matter of dilution of language — rather a general manifestation of imprecision (but not inexactness), where a relative term gets a sideline as an absolute.


What causes a USB Cable to fry a PCB?

Question: When assembling my own USB 2.0 spec cables, I haven't had any experience with frying PCBs they get plugged into (of custom-made keyboards primarily), but I hear stories of it happening. So I'm trying to identify what might cause a DIY'd USB cable to fry a PCB, when it is connecting a peripheral (keyboard) to a host PC? Would transposing the VBUS/GND conductors on one end of the cable do it? Is it even possible in modern PCs that a mis-assembled cable would fry a keyboard PCB? Thanks!
Comment: Yes. And yes...
Answer: If you are shorting the VDD and VSS of the USB, you are not frying the keyboards at first. The Host PC is at the major risk of damaging the whole USB port. The Keyboard would be just an eye witness.
Depends on the Model, make and luck anything of the below is possible:

The USB port will get temporarily disabled
The USB port will let more than 100 mA or even 500 mA to let the cable or the connection fry including itself
USB will fail permanently to work
The devices attached also would fry or fail.

Have a protection feature to protect both your device of the interest and the host:
https://www.littelfuse.com/technical-resources_old/application-designs/circuits/usb2-port.aspx
Answer: Incorrectly wired cable can do damage. Don't miswire them, or at least test them before use.
Data pins are in general not 5V tolerant. If Vbus gets swapped with one of the data pins, the data pin can get damaged, and it can do a lot of damage to whole device if 5V Vbus gets fed to 3.3V supply via internal protection diodes in the USB chip, so all chips may get destroyed with overvoltage on supply.
Swapping Vbus and Ground would swap the input polarity to the device. Sending -5V to any chip that expects +5V might fry it. In case where GND and cable shield are connected in the device, swapped polarity will short Vbus to shield and depending on PCB track width it can act like a fuse so the copper trace will heat up and melt.
Also even a correctly wired cable can do damage if the device has no ESD protection.

What causes a USB Cable to fry a PCB?


What alternatives to the Venn diagram are there to show alignment of 2 things?

Question: The Venn diagram is probably the most common way to show alignment, but we're looking for something more fresh. However, we don't want to require our users to understand advanced math in order to read our graph.
Answer: The Venn Diagram is one of the simplest and easiest to understand ways to show overlapping data. You can still use a Venn Diagram but present it in a fresh way that's more than just two intersecting circles. Like you can use different shapes like diamonds or triangles. I've seen some that showed intersecting similar objects such as coffee cups or faces or light bulbs.
Answer: I agree with Matthew's answer. There are many shapes you can use to show alignment of two things. I use light bulb shapes to show the interactions of things. If you want you can create cute faces on the bulbs; this will help to catch the interest of people.