sudo apt-get update focal and ppa error
What can I do if a repository/PPA does not have a Release file?
How to change fonts I'm sure this is a newbie question, but I can't figure this out. I have tried to follow the advice here:  and here:   But I can not seem to be able to generate any font change. I either get no change or error messages.  Here is the output of one failed attempt to change the font to Times using this command:  \rmfamily \renewcommand{\rmdefault}{ptm}     Apparently I either don't have a correct package installed or...  The output says " Metric (TFM) file not found." but I am not sure where to go from there. I just did a clean installation of Ubuntu 18.04.1 on a tablet which was previously running Ubuntu 17.10. Back then just after the installation the screen was rotated, but I was able to get it to work (I think it was running on Wayland).  Now with 18.04.1 the situation is similar: when Ubuntu first boots the login screen is upside-down, but that's not a problem. This time, after login, the screen is correctly oriented but the mouse cursor is upside down and mouse movements are inverted with respect to both axes. The problem is that when I try to click on something the click is registered on the position on the other side of the screen (symmetrically with respect to the center).   It almost seems like the screen (desktop, application, etc.) is correctly displayed, with also the mouse positioned correctly and moving as it should, but then the mouse cursor which is shown to the user is inverted, like if the screen had been inverted just before drawing the cursor.  I already tried the answers I could find, but none worked for me. Anyone have an idea of what's going on?  Thanks What is the difference between <%# and <%= in ASP.NET MVC? I made a hair particle system and set the Dupli Group to a group of 3 objects. Each of the 3 objects has:   it's origin set to be touching the XY plane (on layer 2) it's Scale applied to 1 and it's Rotation applied to 0     I am trying to get each of the objects to sit directly on top of the ground, but instead, they are centered in the plane, half above the plane and half below the plane:      What am I doing wrong? Here is . Why use foreign keys if cascade action is not need? How about newlines within comments? I am aware that comments have only a simple field, with no formatting possible and that is fine (if formatting is needed, your comment should actually be an answer!)  But I find some comments hard to read because they are mainly one giant line (of up to 600 characters!). Any newlines entered during the redaction of the message is stripped from the published comment.    Would it be possible to preserve those newlines? (but may be deleting empty lines, to prevent abuses like a comment taking 600 lines because a prankster could find amusing to post a 600 newlines comment!)    Let's recap:   what we need (and can actually preview while typing a comment, making it more readable, both for the writer -- and the reader, should newlines being kept): declined for newlines (why? no reason given at this time.) what we don't need but is "nice to have" (even though we cannot preview those): granted for bold and italic text. what we really don't need (and cannot not preview): granted for... __code sample__!? Code sample? Seriously? In a comment?   In short: What was an incentive to post a new answer (because of the lack of formatting) is now further diminished. But the comments remain published as one long-hard-to-read-gigantic line. Are $_SESSION variables stored on the client or the server? See all my questions across all Stack Exchange sites? I have a dell laptop with 4GB of ram and 500GB of storage.I just finished installing windows 8.1 32bit version, which utilizes 3GB of ram.  Can I install and run Ubuntu to utilize that unusable portion of Ram.Then how?  Thanks in advance This morning I upgraded my system to Windows 10 2004, the upgrade went smooth and was through Windows Update. I am using Hyper-V as my virtualization program for virtual machines and to provide extra layer of protection to the system through core isolation. After the upgrade, I noticed that a new Virtual Switch was created with the name &quot;vEthernet (Ethernet)&quot; where &quot;Ethernet&quot; within the parentheses is the name of my primary network adapter. Also noticed this behavior has a specific pattern of creating new vSwitches correspond to the adapters you have, e.g. if you created a new Virtual Switch and restarted the system, a new additional switch will appear with the name &quot;vEthernet (your-new-switch-name)&quot;. Tried to remove Hyper-V and reinstall it but no luck. I am aware of a similar  on SuperUser but has no answers on it. Any clues for the root of the problem? What is the source for defaulting to plain English readings of non-game terms? To date I have had an Apple ID tied to my personal email address. It uses my personal paypal account for the purchases, and currently it has a credit balance thanks to some Christmas iTunes gift cards.  With the App Store recently being released, I'd like to buy an OS X app for business purposes. I don't want to use the credit balance on my personal Apple ID account, so I was thinking about creating a new Apple ID just for when I buy apps that I use for business. This way I could have the business Apple ID tied to my business paypal account.  However, I'm concerned that there might be some gotchas with using two different Apple IDs on the same MacBook by the same user. Before I just try this blindly, does anyone have any experience or know of any gotchas? Why can Naruto still use Rasenshuriken? When Naruto first used Rasenshuriken against Kakuzu the effect was massive. He destroyed   two of Kakuzu's hearts, but there were a huge after effect to him. If I'm not mistaken, Tsunade advised Kakashi to ask Naruto never to use the technique again due to the huge risk. So why is Naruto still able to use the technique and have no side effects after that battle? I may have missed out on something. Relation bewteen Hessian Matrix and Curvature According to ,  It describes the local curvature of a function.   AFAIK, for one-variable function $f(x)$, its local curvature is  $$\kappa = \frac{|f''|}{(1 + f'^2)^{3/2}},$$ and its Hessian matrix is  $$\mathcal{Hess}(f) = [f''],$$ right? And here is my problem, I think the local curvature is not just described by its Hessian matrix, because $f'$ also has its role in it, doesn't it?  And furthermore, for 2-variable function $f(x,y)$, its Hessian matrix is  $$\mathcal{Hess}(f) = \left[ \begin{array}{cc} f_{xx}'' &amp; f_{xy}'' \\ f_{xy}'' &amp; f_{yy}'' \end{array} \right].$$ How does it relate to the local curvature of $f(x,y)$? I'm considering the ring $\mathbb{Z}[\sqrt{-n}]$, where $n\ge 3$ and square free. I want to see why it's not a UFD.   I defined a norm for the ring by $|a+b\sqrt{-n}|=a^2+nb^2$. Using this I was able to show that $2$, $\sqrt{-n}$ and $1+\sqrt{-n}$ are all irreducible. Is there someway to conclude that $\mathbb{Z}[\sqrt{-n}]$ is not a UFD based on this? Thanks. Meta SE account is shown 3 times in accounts Earlier today I asked my first question on this site. So Meta SE was added to my accounts. But this account is shown three times:        One of them also has a badge while the other two don't.   The network profile doesn't show MSE at all:        Also I have got this long wierd user name and  I am not able to change it. In the edit- display name this long name is not there.My user name on other sites is shown there.   After all this happened Meta SE questions are not getting loaded in my SE app.    Edit: the issue of name is solved now. I changed the profile picture and saved changes and it worked. Completely uninstall an app on Lollipop I am having a problem with uninstalling apps on Android 5.0 (Nexus 5). I am developing an Android app, so I debug/run the app directly on my device. For production, I exported the same app with my keystore, uninstalled the debug APK that I ran earlier, tried to install the signed APK, and I got this error:      An existing package by the same name with a conflicting signature is already installed.   Is it because the bytecodes are still in the ART runtime? Anyone has any idea how to solve this? Dimension of Dirac $\gamma$ matrices While studying the Dirac equation, I came across this enigmatic passage on p. 551 in From Classical to Quantum Mechanics by G. Esposito, G. Marmo, G. Sudarshan regarding the $\gamma$ matrices:     $$\tag{16.1.2} (\gamma^0)^2 = I , (\gamma^j)^2 = -I \ (j=1,2,3) $$    $$\tag{16.1.3}  \gamma^0\gamma^j + \gamma^j \gamma^0 = 0 $$   $$\tag{16.1.4}  \gamma^j \gamma^k + \gamma^k \gamma^j = 0, \ j\neq k$$    In looking for solutions of these equations in terms of matrices, one finds that they must have as order a multiple of 4, and that there exists a solution of order 4.   Obviously the word order here means dimension. In my QM classes the lecturer referenced chapter 5 from Advanced Quantum Mechanics by F. Schwabl, especially as regards the dimension of Dirac $\gamma$ matrices. However there it is stated only that, since the number of positive and negative eigenvalues of $\alpha$ and $\beta^k$ must be equal, $n$ is even. Moreover, $n=2$ is not sufficient, so $n=4$ is the smallest possible dimension in which it is possible to realize the desired algebraic structure.  While I got that the smallest dimension is 4, I fail to find any argument to reject the possibility that $n=6$ could be a solution. I also checked  Phys.SE post, but I didn't find it helpful at all.  Can anyone help me? I'm trying to get through my first SalesForce mod and it's definitely been a rocky path. I have one task I'm trying to do, but this section is holding me back.  I have two custom fields.  One a pick list and the other a text box. I have added them to the Approve/Reject Approval Request section in the Opportunity page. I added the fields through the Select Fields to Display on Approval Page Layout and they DO show up on the Approve/Reject Approval Request section. I added them in like ().  However, just the label for the fields show, the field itself is nowhere to be found and can't be used.    You can see and even use the fields when you open the Opportunity page itself, but when you go to use the Approve/Reject, you can't do anything with them or see any values.  I was never a SalesForce user and got this tossed in my lap and really don't know my way around yet. I appreciate any help on this!!  Thanks!!  Kurt Please select a file error