I am getting an error while using the command :   sudo apt-get update   The error:    How can I solve it? since i am new to ubuntu i really dont know much so please help me
PPA seems to be constantly offline. Whenever I use sudo apt-get update, this error is shown:  W: Failed to fetch http://ppa.launchpad.net/ 404  Not Found   How do I fix these errors?
Finding all software packages in Debian that provide a particular alternative The Debian distribution has the . From the Wiki:     The Debian alternatives system creates a way for several programs that   fulfill the same or similar functions to be listed as alternative   implementations that are installed simultaneously but with one   particular implementation designated as the default. For example many   systems have several text editors installed at the same time. The vi   program is a classic example of an editor that has many   implementations such as nvi, elvis, vim, etc. but which one should be   designated as the default?   In general, there are multiple packages in Debian that provide a particular alternative. How does one obtain a complete list of all such packages that exist in the Debian repositories? Let us use the vi alternative as an example.  NOTE: Doing such a query against the list of installed packages is easy, but that is not what this question asks. I have a lidar file (file.las) with the following spatial reference:  Spatial Reference:            PROJCS["NAD83 / UTM zone 11N",     GEOGCS["NAD83",         DATUM["North_American_Datum_1983",             SPHEROID["GRS 1980",6378137,298.2572221010002,                 AUTHORITY["EPSG","7019"]],             AUTHORITY["EPSG","6269"]],         PRIMEM["Greenwich",0],         UNIT["degree",0.0174532925199433],         AUTHORITY["EPSG","4269"]],     PROJECTION["Transverse_Mercator"],     PARAMETER["latitude_of_origin",0],     PARAMETER["central_meridian",-117],     PARAMETER["scale_factor",0.9996],     PARAMETER["false_easting",500000],     PARAMETER["false_northing",0],     UNIT["metre",1,         AUTHORITY["EPSG","9001"]],     AUTHORITY["EPSG","26911"]]   Then I reproject it to WGS84 with las2las:  las2las --a_srs EPSG:26911 --t_srs EPSG:4326 -i file1.las -o output.las   And I get:   Spatial Reference:                GEOGCS["WGS 84",         DATUM["WGS_1984",             SPHEROID["WGS 84",6378137,298.257223563,                 AUTHORITY["EPSG","7030"]],             AUTHORITY["EPSG","6326"]],         PRIMEM["Greenwich",0],         UNIT["degree",0.0174532925199433],         AUTHORITY["EPSG","4326"]]   But when I try to revert the transformation: from WGS84 to NAD83/UTM 11N, I get an error:  las2las --a_srs EPSG:4326 --t_srs EPSG:26911 -i output.las -o wgs2utm.las ERROR 1: latitude or longitude exceeded limits error: Could not project point for ReprojectionTransform::latitude or longitude exceeded limits0.   Why I got this error, if I am just reversing the transformation (originally from NAD83 to WGS84, and then from WGS84 to NAD83)?. is looking bad right now. No errors in the console, but the following files have no content:         The CSS on another subdomain works fine though: Generalised rule for verb usage in simple present tense using participle At the end of a letter, is it correct to omit "I am" in this sentence?     I am looking forward to hearing from you   Then it will become:     Looking forward to hearing from you I am preparing a document in French, using the "babel" package with option "french" and using commands that include colons and semicolons. My problem is, the French spacing before colons and semicolons disappears when the commands are printed. I do not understand why, have not been able to find an answer. Below is a MWE.  \documentclass{article} \usepackage[french]{babel} \newcommand\deuxpoints{Texte: texte} \begin{document} \deuxpoints\ \endgraf Texte: texte \end{document} I recently moved into an in-law unit of a large old house.  In the kitchen, there are two pipes coming out of the wall (one protruding out a little more than the other).  I had assumed they were gas lines to connect my stove.  But since the stove only connects to one pipe, I'm now wondering if they're actually water lines. Can anyone explain how I can tell the difference? On the other side of the wall is a large closet with the air conditioning system, water heater, and what I think is the gas shutoff valve. Blurry Text On Model After Render How can you sync Blender configs between multiple machines? This question is asked often in Ask Ubuntu, sometimes with few hints about the situation.   Please provide a list of possible reasons to help troubleshoot the problem. Is it possible to prove a null hypothesis? How do I center a container in my HTML/CSS? The problem:  Assume $f: \mathbb{R} \rightarrow \mathbb{R}$ satisfies $|f(t) - f(x)| \leq |t - x|^2$ for all $t, x$. Prove $f$ is constant.  I believe I have some intuition about why this is the case; i.e. if $t$ and $x$ are very close, ($|t - x| = \epsilon$), then $\sqrt{\epsilon}$ will converge to 0, so $|f(t) - f(x)|$ will also converge to zero if you keep taking $t$ and $x$ closer and closer to each other. However, how do I formalize this argument? Thanks. If $a^{n}-1$ is prime then $a=2$ and $n$ is prime? Show that $\sum_{n = 1}^\infty n^qx^n$ is absolutely convergent, and that $\lim_{n \rightarrow \infty}$ $n^qx^n = 0$ I'm having trouble with proving the following for my math study:  Let $x$ be a real number with $|x| &lt; 1$, and $q$ be a real number. Show that the series $\sum_{n = 1}^\infty n^qx^n$ is absolutely convergent, and that $\lim_{n \rightarrow \infty}$ $n^qx^n = 0$  I tried this:  $\sum_{n = 1}^\infty n^qx^n$ = $x + 2^q + 3^qx^3 + ...$ $= x(1 + 2^qx + 3^qx^2 + ...)$  So far, I don't know how I have to do this, I tried to apply the root test on this, but for that I would need to compute the lim sup of the series, so I thought that was not correct. Could you explain me how to prove this?  Thanks in advance! Is there anything to do during an 8 hour after-midnight layover in Dubai? We are planning a trip with an 8 hour layover in Dubai spanning from 1am-9am. I am thinking about going to see the city, but is it worth it to do it given the very late night hours? Will at least the outside attractions accessible?   Will Burj Khalifa be visible in the middle of the night?  Will at least some of the malls be open?  Will there be anything to do at night?  I have seen other questions about layovers in Dubai (), but none of them is asking about a night-only stay. I know this proof is somewhat similar, or related to the Baire's Category Theorem but I can't seem to figure out how to do it.  The Baire Category theorem asserts that if X is a complete metric space or a locally compact Hausdorff space (my case), then the complement of a countable union of nowhere dense sets is always nonempty.  How can I use this on the proof? header and footer of the first page of every chapter It maby be weird, I want to make header and footer for every page including the first page of each chapter, how can I do this? GitHub pages are not updating Can a random forest be used for feature selection in multiple linear regression? Since RF can handle non-linearity but can't provide coefficients, would it be wise to use random forest to gather the most important features and then plug those features into a multiple linear regression model in order to obtain their coefficients?