Driving a borrowed Car in the USA as a German Citizen
What documentation is needed for a tourist to drive a US citizen's car?
Is there an online course in Mathematical Methods for Physics, Covering Matrices and Vector Analysis? I am taking a course in Mathematical Methods for physicsPhysics (Junior Level).   We are working from   > Mathematical Methods for physicists, George B.Arfken .    I just need online resources covering ( Matrices, Determinants, Vector Analysis, Tensors and differential forms and Vector spaces...etc) to study and understand from. Retrieve malicious IP addresses from Apache logs and block them with iptables Researching English/Christian families in India during first half of 19th century? I have been researching the meaning of positive semi-definite property of correlation or covariance matrices.   I am looking for any information on   Definition of positive semi-definiteness; Its important properties, practical implications; The consequence of having negative determinant, impact on multivariate analysis or simulation results etc. Why am I getting shopping trolley notifications about local store savings? I am getting "Shopping Trolley" notifications appearing regularly. The notification looks like this:   The notification is about "Store savings" at a local supermarket and that is it!   Is this notification from Google Maps or another application like Google Assistant? I'm struggling to find the specific setting to disable the notification.  I am also interested to know if this notification could in any way be targeted advertising generated by the store. My marketing preferences with the store are opt-out and this strikes me as very dumb advertising. Surely Google isn't doing this? Is there a means that a store can generate notifications like this? Could it be targeted if they have my email address?  These are pain and I want to understand why they are spamming me and disable them without disabling everything else.  I can see various options under Google Maps, settings, notifications. Which setting would apply? Could it be "New on maps, Get occasional updates about new features in your area"? I can't see what setting to suppress!  Thanks for all help. Why does a light object appear lighter in your peripheral vision when it's dark? So, I am not sure I can reproduce it via images, but the steps are:  1) At night, open a window and have a look at the surface of the earth  2) Suppose there's an object that reflects a tiny amount of light  3) When you actually try to focus your eyes at this object, you either don't see anything (depends on the amount of light it reflects) or you can hardly see it  4) When you focus your eyes on something that is 3-10 metres away, you can easily see this object with your ambient vision. Not the details, but it seems that it reflects more light.   Why does it happen? Continuity and existence of directional derivatives at all directions of a $f:\mathbb{R}^{2} \to \mathbb{R}$ given by $f(x,y)=\frac{2x^2y}{x^2+y^2}$ Let $f(x,y)=     \begin{cases}       \frac{2x^2y}{x^2+y^2} &amp; if &amp; (x,y) \neq (0,0) \\       0       &amp; if &amp; (x,y)=(0,0) .  \end{cases}$  (i) Prove the directional derivatives of $f$ exist in any direction at the point $(0,0)$.  (ii)¿Is $f$ continuous on (0,0)?  For (i) I took $u=(u_{1},u_{2}) \in \mathbb{R^{2}}$ such $\|u\|=1$ and $0=(0,0)$. So $$\lim_{t \to 0} \frac{f(0+ t u)-f(0)}{t}=\lim_{t \to 0}\frac{2(tu_{1})^2 (tu_{2})}{(tu_{1})^4+(tu_{2})^2}=\lim_{t \to 0}\frac{(t^2 u_{1}^2)(t^2 u_{1}^{2}) tu_{2}}{t^{4}u_{1}^{4}+t^{2} u_{2}^{2}}.$$ But I cannot find the limit when $t$ aproaches to $0$. Which by finding them I would prove the directional derivative exist at every direction right?  For (ii) I got the intuition $f$ is not continuous at $(0,0)$ so I took $\lbrace (\frac{1}{k},\frac{1}{k}) \rbrace_{k \in \mathbb{N}}$ and $\lbrace (\frac{1}{k},0) \rbrace_{k \in \mathbb{N}}$ which are two different sequences in $\mathbb{R}^{2}$ converging to $(0,0)$. However, $\lbrace f(\frac{1}{k},\frac{1}{k}) \rbrace_{k \in \mathbb{N}}=\lbrace \frac{1}{k^{2}} \rbrace_{n \in \mathbb{N}} \to 0$ and $\lbrace f(\frac{1}{k},0) \rbrace_{k \in \mathbb{N}} \to 0$. So maybe my intuition was not right? Can anyone help me end the proof of continuity or not continuity , please? Centering figure captions in IEEEtran I am working on a paper using the IEEEtran template in LyX.  I have run into a problem: While the contents (in this case, a table) of the figure float are centered, the caption is aligned to the left (see screenshot below). How can I center the caption as well?    This is generated by the following LyX document:    What I've tried:   Center the table (the table is centered) Center all the contents in the float (only the table is centered) Select the caption and center it (no effect)   Technical details:   LyX 2.0.5.1 Mac OS X 10.7.5 (Lion) All centering was performed by Right Click>Paragraph Settings>Align: Center Story where the main character learns to perceive time out of order from the aliens I read a story several years ago in which aliens come make first contact with Earth, and a bunch of scientists set to work trying to establish communication with them in various fields. The main character is a linguist and her team is working to try to figure out their written language, which doesn't have any sort of linear structure and can be read starting from any place.  It contains some explanation of quantum physics as an analogy for how they view time.  In the end, it turns out that the aliens don't perceive time in a linear fashion, and sort of see the future on equal terms with the past, etc. The main character learns to see time this way by studying their language, and the story is interspersed with her talking about what her child is going to do / is doing / has done.  I think I read it in a science fiction magazine but I'm not sure about this part. Why will Ubuntu no longer measure file size unit as byte, megabyte, gigabyte, etc? I read on  that Ubuntu will no longer use the familiar file size units we all know by now (kB, MB, GB, TB) and switch to a different IEC standard (KiB, MiB, GiB, TiB). If this is true, I would like to know what's the reasoning behind this change, and the impact (if any) this change has, especially with multiplatform applications or applications run with Wine. How do I get lightning:datatable to do some undocumented thing X? What is wrong with defining \bal as \begin{align}? Getting started with neural networks for forecasting How to set default style for arrow tips in TikZ? When my phone starts up there are several application/services running in the background that I would rather not.  And when I press the Home button while using an app, that app usually goes into the background without exiting.  How can I stop these apps from running? How to shut down the computer safely by pressing the power button? So this is pretty simple: when I press the power button whilst the machine is on, it comes up with a menu (of which one of the options is to shutdown)  However, I just want it to just start shutting down once I press the power button without any further interaction!  How do I accomplish this? I  just got these 10 e-mails 5 hours ago from do-not-reply@stackexchange.com:      Recently, you asked a question on [X] Stack Exchange, but you haven't verified your email address yet.      Click on the following link to verify your email and set a password so that you can log in.      Here, [X] refers to all of the following:    GameDevelopment.SE SharePoint.SE Unix.SE  Skeptics.SE Japaneese.SE HomeImprovement.SE SciFi.SE PersonalFinanceMoney.SE  DatabaseAdmins.SE  TeX.SE    I haven't posted on any of these except for TeX.SE, but that was not recently, and through my real account.   =   I asked about this , and was told that someone seems to be impersonating me by using my email. Is it possible for staff to stop this?   Also, I'm pretty surprised there is no measure to stop people from using emails to existing SE accounts (see for example, on wordpress.com, if you use an e-mail which has an existing account on wp.com, you are asked to log in.).    EDIT:  I just got 2 more emails an hour ago for SharePoint.SE, and for AmateurRadio.SE. I'm completing a problem set, one problem for which I literally have no idea what to do on. The graders would prefer to have a physical copy of the problem so I thought it best to include the ¯\_(ツ)_/¯ emoji as my answer, instead of something like "Dunno" or "No idea."  Option #1 is to include an image.  Beyond that I actually don't understand how this emoji works. The middle character is Japanese kana "tsu" and proves problematic - TeX wants it in math mode then renders "?" when it is. "Distribution not supported" when trying to install Intel Graphics Installer in Ubuntu I just did a clean install of 20.04 and I noticed that no key shortcuts for files manipulation work when my focus in on Desktop (not in Nautilus).   When I have copied a file to clipboard, I cannot Ctrl+V it to Desktop, when I click on a file on Desktop, I cannot Ctrl+C it, or I cannot Delete it with keys. Only ways to do it is either navigate to the Desktop folder in Nautilus, or right-click the file on the Desktop and copy/move to trash/paste...  Sorry if I'm missing something obvious, all the key shortcuts worked normally for me in 18.04.