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What could cause java.lang.reflect.InvocationTargetException? Addition with NULL values Is there a spec that the id of elements should be made global variable? How to reinstall Ubuntu keeping my data intact? I want to reinstall Ubuntu keeping my data intact. I have 160 GB hardrive (sata or pata I don't know but it's slim and made in China) with a 40 GB ext3 partition, a 4GB swap memory and 3 other partition with a FAT32 file system. I have around 4GB space on my drive where Linux is installed.  I'd like to keep the data intact, especially the Downloads folder, desktop, and /var/www; And I no longer have access to any other machines or external storage devices. What is a combo update and how is it different than the regular update? What is a combo update and how is it different from a normal update? ERD for a web development company I am working on an ERD which represents the relationships between entities in a Web development company behavioral model. There I have entities like:   Customer Service ----------- (like: web development, web design, web consultation, ...) Order-item ------- (like: web development, web design, web consultation, ...) Order Invoice Project Project-phase Task --------------- (like: web development task3, web design task7) Developer Delivery ----------- (like: the developed web app, web consultation session, ...)   I have this diagram so far, though I know it still has major problems, and it is just for a start point:    Main concept   Customer makes order-items on services, combined to form an order which relates to an invoice. Each project has multiple project-phases with each project-phase related to an order. Each project-phase has multiple tasks, each of which is assigned to a developer. Each project-phase has a delivery, which will be delivered upon payment of the related orders invoice.   Questions   Are has and contains completely the same? If not, how to choose between them for relationships?! what is the measure?! Are there any rational problems with the Main concept section? Any helpful ideas or suggestions to improve this model?   Any help with this, would be really appreciated.  Update 1  Refined version of the diagram     Update 2  Considering an analogy of a Fast food restaurant would be helpful:   Customer ---------- A hungry person Service ------------- Making a burger, Home delivery, Mobile delivery, ... Order-item --------- A burger, ... Order ---------------- A home-delivered burger Invoice -------------- The printed invoice Project -------------- Serving the customer for a complete year (like a contract) Project-phase ----- Serving the customer for a single day Task ----------------- Preparing the kitchen, process the meat, ... Developer ---------- The cookie Delivery ------------- A burger in wrapped in wax papaer and a drink with the tray   Update 3  ()     Project seems to be unrelated to Customer in your diagram. Is this what you intended?   I think Order is and Project should not be related, as I think it is something off-the-counter and customer has nothing to do with it. she/he is only after the delivery and is concerned about time and money, nothing else. Please tell if I am wrong.     Are all Orders part of a Project or can you have orders that aren't in a project at all?   All Orders are part of a project, except those new ones which are waiting in the process queue.     Similarly, you relate order item directly to customer, but also to order. Are orders split between customers?   Please think of Order-Item as these:   web design web design consultancy domain name consultancy ...   So, customer choose some of these items, collected as an Order which has an invoice and could be paid. Order-Items are directly related to offered Services. I don't understand what do you mean by Are orders split between customers?.     If not you don't need a ternary relationship between customer, order item and service. Rather, an order item is an intersection between order and service. Order items belong to customers by inheritance from order (or even project?)   This is somehow true: Order items belong to customers by inheritance from order, but I think it is more rational to say it like this:     Order-Items, inherited from Service, belong to Order which itself belongs to Customer. Difference between projection and datum? latex table border dont appear / to big / to small still working on that table. Here's my new question reguarding the table borders:  It appears, that i do something wrong setting boarders. Here is my code, and a screenshot:  \documentclass{article} \usepackage{multirow} % Used for the vertical cells \usepackage{rotating} % Used for the vertical cells  \usepackage{xcolor} % Used for cell-colors \usepackage{colortbl} % Used for cell-colors  \usepackage[a4paper]{geometry}% Used to set the pdf margins manually \newgeometry{left=2cm,bottom=0.1cm}  \definecolor{grey}{HTML}{F2F2F2} % Define grey for the cells \definecolor{red}{HTML}{FF0000} % Define red for testing  \begin{document} \scriptsize % Use a small font size  \begin{tabular}{|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0.6cm}|p{0,6cm}|}  \cline{10-17}  \multicolumn{9}{|c|}{} &amp; \multicolumn{2}{p{\dimexpr (0.6cm)*2+2\arrayrulewidth+2\tabcolsep\relax}|}{\cellcolor{grey}Work to retired ratio} &amp; \multicolumn{4}{p{\dimexpr (0.6cm)*4+1\arrayrulewidth+2\tabcolsep\relax}|}{Health care sizing (per thousand)} &amp; \multicolumn{2}{p{\dimexpr (0.6cm)*2+1\arrayrulewidth+2\tabcolsep\relax}|}{\cellcolor{grey}Inverse dependency ratio}\\\cline{3-9}  \multicolumn{2}{|c|}{} &amp; \multicolumn{4}{c|}{\cellcolor{grey}Population (mio.)} &amp; \multicolumn{3}{c}{Workforce (1000)}  &amp; \multicolumn{2}{|c|}{\cellcolor{grey}} &amp; \multicolumn{2}{l|}{Physicians by} &amp; \multicolumn{2}{l}{Nurses by} &amp; \multicolumn{2}{|l|}{\cellcolor{grey}Old agers by}\\\hline  \multicolumn{2}{|c|}{} &amp; \begin{sideways}\cellcolor{grey}\parbox{4cm}{Overall}\end{sideways} &amp; \begin{sideways}\cellcolor{grey}\parbox{4cm}{Young age}\end{sideways} &amp; \begin{sideways}\cellcolor{grey}\parbox{4cm}{Working age}\end{sideways} &amp; \begin{sideways}\cellcolor{grey}\parbox{4cm}{Old age}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Overall}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Physicians (Proj: 2025)}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Nurses (Proj: 2030)}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{\cellcolor{grey}Working age by Old age}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{\cellcolor{grey}Work force by Old age}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Workforce}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Working age}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Workforce}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{Working age}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{\cellcolor{grey}1 physicians}\end{sideways} &amp; \begin{sideways}\parbox{4cm}{\cellcolor{grey}1 nurse}\end{sideways}\\\hline  \multicolumn{2}{|l}{USA} &amp; \multicolumn{4}{l}{\cellcolor{grey}} &amp; \multicolumn{3}{l}{} &amp; \multicolumn{2}{l}{\cellcolor{grey}} &amp; \multicolumn{4}{l}{} &amp; \multicolumn{2}{l|}{\cellcolor{grey}}\\\hline  1990/1 &amp; &amp; 248,6 &amp; 71,3 &amp; 146,1 &amp; 31,2 &amp; 127.500 &amp; 615,4 &amp; 1491,6 &amp; 4,68 &amp; 4,09 &amp; 4,83 &amp; 4,21 &amp; 11,70 &amp; 10,21 &amp; 50,7 &amp; 20,9\\\hline  1 &amp; 2 &amp; 3 \\\hline  \end{tabular}  \end{document}     On 1 the Top border of Population is not visible although i did used \\\cline{3-9}\cline{12-17} on that line.  In 2 both borders are pushed a bit to the right for no reason i can see.  And in 3 again the top borders are not visible despite using \cline{10-17} on that line. What did i do wrong?  Thanks! Scanner issue when using nextLine after nextXXX Does Windows use the fastest drive for the page file? Suppose I have a 6 GB page file on an SSD and another 6 GB page file on a traditional mechanical 5400rpm SATA drive.  Does Windows take into account the difference in the performance characteristics between the two drives when deciding which page file to use?  If it matters, I'm asking about Windows 7 and higher.  I reviewed this  but it doesn't appear to factor in the case of dissimilar storage speeds. Recreate plot when data file changes Is it possible to use the TikZ/external library and have pgfplots recreate a figure when a data file that is plotted changes? Say I have something like the following:  file.tex:  \documentclass{article}  \usepackage{tikz,pgfplots} \usetikzlibrary{external} \pgfplotsset{compat=newest} \tikzexternalize \newcommand{\figFilename}{}  \begin{document}   \begin{figure}[t]     \centering     \renewcommand{\figFilename}{thePlot}     \tikzpicturedependsonfile{\figFilename.tikz}     \tikzsetnextfilename{\figFilename}     \input{\figFilename.tikz}     \caption{The caption.}   \end{figure} \end{document}   thePlot.tikz:  \begin{tikzpicture}   \begin{axis}[     xlabel={$x$},     ylabel={$y$},]     \addplot+[only marks,mark=x]       table[x=x,y=y] {data.dat};   \end{axis} \end{tikzpicture}%   data.dat:  x y 0 20.44 1 20.06 2 19.76 3 19.54 4 19.40 5 19.34   If I change thePlot.tikz, the external library will detect that the figure is no longer up-to-date and recreate it. Is it possible to have the same effect when any of the plotted data files changes as well? I tried something along the lines of \tikzpicturedependsonfile{data.dat}, and it doesn't work. That wouldn't be an ideal solution anyway, as most times I use many data files in each plot and listing all dependent files manually would be more pain than gain.  So is there an easy, automated way for the external library to check all data files included in a tikzpicture and recreate the plot if at least one of them has changed? How can I search for special characters? Finding how multiplication and addition behave on $\mathbb{F}_4$ without any result I'm currently tutor in an undergraduate course and the students are asked to find how addition and multiplication behave on the field with 4 elements: $\{0,1,x,y\}$. In the solution the teacher gave me, he uses the fact that $(\mathbb{F}_4^*, \cdot )$ is cyclic with order 3 to find that $x$ and $y$ are both generators and that $(\mathbb{F}_4,+)$ is a group of order 4 to deduce that $0=1+1+1+1=(1+1)(1+1)$ and hence, $(1+1)=0$ since a field is integral.   However, I'm not satisfied with this reasoning because this question is asked to student in first year and they juste have been introduced to fields (and this was part of an analysis course so they won't see any result soon). So I tried to find how it behaves by myself, using as few results as possible.  Multiplication is the easy part, $0\cdot a$ and $1 \cdot a$ is trivial for all $a\in \mathbb{F}_4$. Then, $x\cdot y\not = 0$ because it is invertible, and it can't be equal to $x$ or $y$ because that would imply the other element to be equal to $1$. Hence, $x\cdot y=1$. We are left to find what is $x^2$ (and similarly, $y^2$). $x^2$ cannot be $0$, nor $x$. If $x^2=1$, then $y=(x^2)y=x(xy)=x\cdot 1=x$. Contradiction. Hence $x^2=y$ and by the same reasoning, we have $y^2=x$.  It was easy with the multiplication, but I can't figure out any non-trivial result concerning addition. My intuition tells me that distributivity should be used here but I'm feeling like it's just converting a problem into another one because we don't know anything about addition.  Does anyone here have an idea of how addition can be "found" without using any advanced result (or as few results as possible)?  Thanks in advance. Does adding two linear equations will result in a line which will pass through an intersection of the linear equations? I was wondering why it is almost impossible to find a geometrical explanation of why adding two linear equations helps us to find a solution of a system of linear equations? Am I right that adding two linear equations will result in an equation of a line which will pass through a point where two linear equations intersect?  If it is right then I completely don't understand why such a crucial point in understanding how to solve systems of equations is never properly taught even at a university level. When to use IComparable Vs. IComparer I'm trying to figure out which of these interfaces I need to implement. They both essentially do the same thing. When would I use one over the other? Why are the Ringwraiths fearful of coming into contact with water? At least twice in The Lord of the Rings: The Fellowship of the Ring, Ringwraiths cower away from bodies of water.  The second time (the ford of Bruinen) can be explained away by their fear of some Elvish magical trap through the enchantment of the water; but what about the first time, at the ferry? One of the Nazgûl could have easily made the jump onto the barge and quickly dispatched those pesky Hobbitsses. Solving linear congruence (modular inverse or fraction) via gcd Bezout equation Isn't finding the inverse of $a$, that is, $a'$ in $aa'\equiv1\pmod{m}$ equivalent to solving the diophantine equation $aa'-mb=1$, where the unknowns are $a'$ and $b$? I have seem some answers on this site (where the extended Euclidean Algorithm is mentioned mainly) as well as looked up some books but there is no mention of this. Am I going wrong somewhere or is this a correct method of finding modular inverses? Also can't we find the Bézout's coefficients by solving the corresponding diophantine equation instead of using the extended Euclidean Algorithm? Check to see if an email is already in the database using prepared statements How to show that $C=C[0,1]$ is a Banach space Let $C=C[0,1]$ be the space of all continuous functions on $[0,1]$. Define $\|f \|=\max \ |f(x)|$. I want to show that $C$ is a Banach space.     Below is my attempt and I was wondering if it's ok.    I know I have to show that $C$ is a complete normed space. Clearly, $\|f\| \geqslant 0$ and $\|f\|=0 \Leftrightarrow f=0$. $\|cf \|=\max~|cf(x)|=|c|\max |f(x)|=|c| \cdot \|f\|$. $\|f+g\|=\max~|f(x)+g(x)|\leq \max~|f(x)|+\max~|g(x)|=\|f\|+ \|g\|$. So $C$ is a normed space.   Next, I show that every Cauchy sequence in $C$ is convergent. Let $\{f_n\}$ be a Cauchy sequence in $C$. Let $\varepsilon \gt 0.$ Then $\exists$ an $N_1$ such that $$ \max~|f_n(x)-f_m(x)| \lt \frac{\varepsilon}{2}$$ for $n, m \gt N_1$ and $x\in[0,1]$.  But there is a subsequence $f_{k_n} $, which converges to $f$. So $\exists$ an $N_2$ such that $$ \max~\left|f_{k_n} - f\right|\lt \frac{\varepsilon}{2}$$ for each $n\gt N_2$.  Now Let $N = \max\{N_1, N_2\}$, if $n \gt N$ then $k_n \geqslant n\gt N$. So we have $$ \max~\left|f_n(x) - f(x)\right| \leqslant \max~\left|f_n - f_{k_n}\right| + \max~\left| f_{k_n} - f\right| \lt\frac{\varepsilon}{2} + \frac{\varepsilon}{2} = \varepsilon.$$  Thus, $\|f_n-f\| \to 0$ as $n\to \infty$. $\quad \square$  Thanks. Is this correct?     The person with whom I'm doing the project should be here soon.   If it is, is with always a dative preposition (like mit in German)?