Null reference on SQLite query
What is a NullPointerException, and how do I fix it?
When using sudo to allow edits to files, I regularly get 'permission denied'.  For example, my mouse is jittery and sluggish, so I want to disable polling:  sudo echo "options drm_kms_helper poll=N"&gt;/etc/modprobe.d/local.conf   I'm prompted for a password, and then get:  bash: /etc/modprobe.d/local.conf: Permission denied   So I tried to do a temporary change to disable polling by using:  sudo echo N&gt; /sys/module/drm_kms_helper/parameters/poll   Yet again the system responded with:  bash: /sys/module/drm_kms_helper/parameters/poll: Permission denied   Any ideas? Create a bootable USB on a Mac to install Ubuntu on a PC Prove that for every $f$, a bilinear form, there exists a basis ${v_1,...,v_n}$ so that $f(v_i,v_j) = -f(v_j,v_i)$ I didn't want to bloat the title, i'll also add that the basis is in ${\mathbb{R}^n}$. This question seems kind of easy, but its from a test so I assume there is a catch here somewhere.   I tried to prove it by contradiction. Assume by contradiction that there exists no basis that satisfies the condition. But as known, every bilinear form can by identified by a matrix so that $A_{ij} = f(v_i,v_j)$. If there is no basis so $f(v_i,v_j) = -f(v_j,v_i)$ it means there is no skew-symmetric matrix which can identify a bilinear form over $\mathbb{R}$ which is obviously not true( I guess an example can be given here, I think ).  This proof just seems to simple to be true, but I can't seem to figure what could be wrong with it. I'll greatly appreciate any tips, thanks! How to succeed with making omelette Let $a$ be an element of a group G. Prove that $a$ commutes with each of its conjugates in $G$ iff $a$ belongs to an abelian normal subgroup of $G$.   My Try:  I proved the backward direction. For forward one, given $g\in G, a(gag^{-1})=(gag^{-1})a$. I was trying to prove that $a\in Z(G)$. In order to prove that, I must show that $ag=ga$. But failed. Am I on the right track? Can anybody please give me a hint? I want to try it myself. In The Force Awakens, Finn and Poe steal and escape in a TIE wearing no personal life support apparatus. TIEs have been upgraded with shields, hyperdrives (for "/sf"), weapons etc, but as far as I know they weren't upgraded with built in life support.   Finn and Poe should have frozen and/or suffocated after hitting space in the TIE. In the Rebels series, Sabine did the same thing. I've looked at what Wookieepedia states about the TIE as well as the old video game Star Wars "TIE Fighter".  Does the movie or any other work explain how Poe and Finn survived? Garbage Collection: Is it necessary to set large objects to null in a Dispose method? After reading  It seems that there is no perfect solution for getting rid of the stretch at the poles of UV spheres.  According to , icospheres can be used for stretch-less UV mapping:     All faces have the same area, which may be useful for certain types of UV mapping containing non-organic textures. An example that comes to mind is an isocahedral die or billiard balls where stretch must be minimized near the point where the number is printed onto the ball.   Incidentally, a lowish-poly billiard ball is exactly what I'm attempting to create.  However, my attempts at neatly unwrapping an icosphere have mostly failed (smart UV unwrap works perfectly for using baked textures, however I was hoping for something more like the example in the 6th post of , with a nice clean rectangular map).  How can an icosphere (I assumed the term "geosphere" in the thread was referring to a (geodesic) sphere made of triangles, like an icosphere) be cleanly unwrapped? Or if it's not possible, is there another way to do this which I'm missing?    I'm planning on using the resulting sphere in the BGE. How can I change media volume when no media is being played? Sometimes I want to play games in (near) silence, and don't like the background music to disturb people. If I use the volume buttons, the ringtone volume is changed instead of media volume. When I'm already in the game, the volume buttons do change the volume of background music, but it's kinda too late.  Is there a way for me to change the media volume to a level I like, from the home screen, before starting apps/games? I am looking for a story about the future of mankind, in which most people have been enslaved in a virtual reality. It ends with the revelation that the people are just lying there imagining their lives with their heads in a trough of feed.  It explains that chemists began to create compounds that could be released into the air to manipulate citizens - causing them to live, shop, think as desired by whoever was in charge. Eventually these tools got subtle enough that they could simulate reality using just these airborne compounds.  This was clearly a prescient view of what later became computer-based virtual reality fiction. Taking the second derivative of a parametric curve In Salesforce Marketing Cloud (SFMC), I want to unsubscribe a contact from a single publication list by using a form on a landing page.  I also want to create an Unsub event in SFMC when they submit the form.  There is some sample code from SFMC Help documents  that seems to do that for external sites. Will it work in a SFMC hosted landing page? Do I need to edit the code much? Every time I try update (using sudo apt-get update) my Ubuntu I get this problem:  W: The repository 'cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1) xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. W: The repository 'ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-amd64/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs E: Failed to fetch cdrom://Ubuntu 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)/dists/xenial/main/binary-i386/Packages  Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found E: Failed to fetch ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.   How can I fix it? I use Ubuntu 16.04 LTS How do you find all $n$ such that $\phi(n)|n$ "ImportError: No module named _struct" configuring python-minimal When I run sudo apt-get upgrade, the dpkg error appears and interupts the process.  Error details:  Setting up python-minimal (2.7.3-0ubuntu7.1) ... Traceback (most recent call last):   File "/usr/local/lib/python2.7/runpy.py", line 162, in _run_module_as_main     "__main__", fname, loader, pkg_name)   File "/usr/local/lib/python2.7/runpy.py", line 72, in _run_code     exec code in run_globals   File "/usr/local/lib/python2.7/compileall.py", line 16, in &lt;module&gt;     import struct   File "/usr/local/lib/python2.7/struct.py", line 1, in &lt;module&gt;     from _struct import * ImportError: No module named _struct dpkg: error processing python-minimal (--configure):  subprocess installed post-installation script returned error exit status 255 dpkg: dependency problems prevent configuration of python:  python depends on python-minimal (= 2.7.3-0ubuntu7.1); however:   Package python-minimal is not configured yet.   And this problem leads to a series of dependency problems when processing the following packages:    python  gwibber-service  libgwibber3  libgwibber-gtk3  gwibber  gwibber-service-facebook  gwibber-service-identica  gwibber-service-twitter  python-all  python-dev  python-all-dev  python-apt  python-problem-report  python-apport  python-libxml2  unity-lens-gwibber  unity-scope-video-remote   Finally, nothing I can do for this problem. And several days later, the root directory is full and I even could not uninstall any software because of this problem. Why isn't Obi-Wan's ghost young? One of the changes made to the Special Editions of Star Wars: Episode VI: Return of the Jedi was at the end of the film.  Luke sees 3 ghosts during the celebration on the forest moon of Endor, Yoda, Anakin, and Obi-Wan.  In the Special Editions, the actor who played Anakin earlier in the film, Sebastian Shaw, is replaced with Hayden Christiansen who played young Anakin in Episodes 2 and 3.  My question is, why is Anakin the only one de-aged?  Shouldn't Obi-Wan also be his younger self, along with Yoda? What's the parameters atribute in apex:canvasApp used for? I'm experimenting with the  feature, and embedding it in a Visualforce page, from where I hoped I would have some control over the canvas.  Now, the apex:canvasApp has a property called  and it's description says that they're parameters passed to the canvas app.    When I don't use the parameters attribute the canvas page draws normally, and using firebug I can see the call to the ip address of the canvas app. But for it to be useful to me I need to pass some parameters to the canvas page and when I do use the parameters attribute the canvas simply does not show, and in firebug it does not show any call to the ip of the canvas.  How are these parameters passed or how can one catch them? Using firebug, in the call to the ip of the canvas app, I can't see any of the parameters that I'm trying to pass.  Here's the simple code I'm experimenting with:  &lt;apex:page &gt; &lt;apex:canvasApp applicationName="Test Canvas" height="400px" width="750px" parameters="{vst_cli: '1293'}" /&gt; &lt;/apex:page&gt;   Inside the parameters attribute I've tried some different things: "{vst_cli: '1293'}" "{vst_cli: 1293}" "{'vst_cli': '1293'}" All of which had the same effect.  Any help or pointers will be welcome.  Thanks in advance. Generating a DEM and DSM from correct LiDAR point classification I have downloaded classified LAS data from    I am trying to generate accurate DEM and DSM for further analysis. I created a LAS dataset with a projected CRS of  NAD_1983_UTM_Zone_19N in meters and the z CRS in meters as well. My question is on which classifications do I choose for the DEM and DSM. Here is the filter options I have in my dataset:     According to unh LiDAR data report class 2 is ground.     What I have done so far:  DEM I chose the class 2 points and used the las dataset to raster.   DSM In the predefined settings I chose first return and used the las dataset to raster tool.   Is this an accurate way of generating these two rasters? Do I not have to take into account the the unassigned class 1, noise class 7, reserved 11, reserved 17, reserved 18?  Additionally (I can ask this as a separate question if it gets requested to), when using the las dataset to raster tool the sampling value is defaulted to 10. I would like to change it to 2 or 3 (would be meters) to match the LiDAR resolution. I also plan on using the generated DEM and DSM for a least cost path analysis and I want them to be higher resolution. Will making the sampling_value 2 or 3 throw off the results or should I leave it at 10? No Wifi, HP Pavillion 15 Ubuntu 14.04 How to clip an Openlayers OSM Background to a Vector Boundary?