I’ve got 3 portable hard drives one is 160GB, the other two are 500GB. I want to write zeros to them using Linux and . I found this command:   dd if=/dev/zero of=/dev/sda bs=?   How for the block size, what is the ideal block size for my 3 portable hard drives? (Note: I placed the ? at the end of the command.)
I use dd in its simplest form to clone a hard drive:  dd if=INPUT of=OUTPUT   However, I read in the manpage that dd knows a blocksize parameter. Is there an optimal value for the blocksize parameter that will speed up the cloning procedure?
Python scope: "UnboundLocalError: local variable 'c' referenced before assignment" I have a 2x2 experimental design. In the experiment, I also collected the participants' professional qualifications (categorical variable- yes /no). I would like to test the effect of controlling this variable on the MSE. I understand that in ANCOVA, the covariate is either an interval or ordinal variable. So should I refer to the test as an ANCOVA if I include professional qualification as an additional variable? Or should it be a blocking variable since &quot;prof. qualification&quot; is categorical. I want to know by an example how prices in stock market changes Let us assume there is a listed company x. Currently it has 100 shares issued to trade in free float market. Current price of stock is let say 10. Now please let me know if I purchase one share of company x at the market price of 10. How it will effect the stock price. And please add and exemplify some other scenarios whichever you find good to explain more. For more information let say promoters of the company holds 100 shares with them like 50% of the company is with promoters and the other half is with people who invest or trade in that company. If I've missed to tell or assume any other vital info. needed please assume it yourself while mentioning it. Thank You Does Android hide some amount of RAM from the User? I bought a new tablet, but Android (2.3.1) shows that it has only 150MB free of 256MB, and it should have 512MB.  I checked the file /proc/meminfo, MemTotal information. It only shows 256MB. Is there a possibility that the Android "hid" 256MB of RAM from the user? A map is continuous if and only if for every set, the image of closure is contained in the closure of image apt: how to be sure that a specific package gets installed/updated from specific repository and not from the default one? Canadian visa rules for flight connections I know that in the US foreigners must have a US visa if they have a connection in the US, even if they fly from a different country to a different country. That is because in the US you have to go through passport control regardless of your final destination.  What is the situation in Canada? Does a person who would need a visa to enter Canada need a visa to connect through Canada without exiting the airport? Showing that $Q_n=D_n+D_{n-1}$ Let $T_n$ be the set of permutations of $\{1,2,\ldots,n\}$ which do not have $i$ immediately followed by $i+1$ for $1\le i\le n-1$; in other words, let \begin{align} T_n=\{\sigma \in S_n: \sigma(i)+1\ne\sigma(i+1) \text{ for all } 1\le i\le n-1\} . \end{align} Let $Q_n$ be the number of elements of $T_n$.    Let $D_n$ be the number of  of $\{1,2,\ldots,n\}$.  It is not hard to show algebraically that $Q_n=D_n+D_{n-1}$, but I am having difficulty coming up with a combinatorial argument to show why this is true.  (I believe there are $D_{n-1}$ elements of $T_n$ that leave $n$ fixed, and $D_n$ elements of $T_n$ that move $n$, but I don't know how to justify this combinatorially.) I have some data which looks like:  sampleA    ATGC    10   100 sampleA    ATGC    120  230 sampleA    ATGC    200  110   I want to print the min and max using the values in both column 3 and 4. So my output should look like:  sampleA   10  230   Thanks in advance Finding the dual basis for the space of polynomials of degree $\leq$ 2 What graphics packages are there for creating graphics in LaTeX documents? What packages do you use and recommend for creating graphics in your LaTeX documents?     As this is a community wiki post, please add your package to the accepted answer (or add a comment, and someone with >100 rep will add it to the CW answer), and include a brief description of what differentiates it from others and how it can be used (GUI drawing tool which generates code, type in raw text, or generates image for inclusion in document).   We'll eventually sort these answers under headings. Here are some options I thought of, not sure which is the right one.   There was an I/O error reading from the pipe. The process writing to the other end of the pipe died with a failure. All processes who could write to the pipe have closed it. The write buffer of the pipe is full. The peer has closed the other direction of the duplex pipe. Writing failed because there are no processes which could read from the pipe. A system call returned the EPIPE error, and there was no error handler installed. List View Visibility I'm trying to show that $R = \mathbb{Q}[X,Y]/(Y^2-X^3)$ is not a UFD, but I got stuck.  To prove this, I could try to find two "different" factorisations for one element, but I am not familiar with this, so I tried to use a lemma and one of the previous exercises. If my syllabus is right, in every UFD counts $$ x \ \text{is irreducible} \quad \iff \quad x \ \text{is prime}$$ My syllabus also states that the elements $\bar{X}, \bar{Y} \in R$ are irreducible. So I tried to show that at least one of the elements $\bar{X}, \bar{Y} \in R$ does not generate a prime ideal.  This would mean that I should find two polynomials $f,g \in \mathbb{Q}[X,Y]$, such that  $$\exists p \in \mathbb{Q}[X,Y], \quad fg - pX \in (Y^2-X^3)$$ and $$\forall q \in \mathbb{Q}[X,Y], \quad f-qX \notin (Y^2-X^3) \ \wedge \ g-qX \notin(Y^2-X^3)$$ or the same thing but then for $Y$.  I hope that you can tell me if this approach is correct, and provide me a hint. I'd appreciate it if you told me the solution, but please start your answer with a hint, clearly separated from the rest. I have a .csv file of coordinates that looks like this:        Is there a way for QGIS to plot coordinates formatted like this?  I've tried Adding a Delimited Text Layer... in QGIS, but do not see any options appropriate for this format:  Nxx.xx.xxx Wxxx.xx.xxx   I am able to use a  website to convert that data to Decimal Degrees, Degrees, Minutes &amp; Seconds, and UTM.  For example, inputting N39.56.854 W074.28.013 outputs a latitude of 39.947567, and longitude of -74.466883.  However, I would like to stay in QGIS and make the same conversion.  Things I've tried:   Created a new .csv that has formatting that matches the output of coordinate conversion site mentioned above, and with separated lat-long columns:     However, using the QGIS Add Delimited Text Layer... option yields no visualization of the points. Suppose Alice chooses a random Prime $p$ and a random private Key $a \in \mathbb{Z}^*_p$. By accident, she also chooses a random number $g \in \mathbb{Z}^*_p$, which is not a generator of $\mathbb{Z}^*_p$ and therefore  $$\langle g\rangle \subset \mathbb{Z}^*_p$$  as opposed to $\langle g\rangle = \mathbb{Z}^*_p$, which would yield a valid key. Alice then computes $A \equiv g^a \pmod{p} $ and publishes the Tuple $(p,g,A)$ as her public key.  Bob now encrypts a message $M$ using Alices public key by computing  $$C_1 = g^b \pmod{p}$$ $$C_2 = M \cdot A^b \pmod{p}$$  Is it possible for an attacker (Eve) to distinguish a “real” ciphertext $(C_1,C_2)$ from a random ciphertext $(Z_1,Z_2) \stackrel{$}{\longleftarrow} \mathbb{Z}^*_p$ with significant advantage (say $Adv \geq \frac12$)?    Edit: I guess it should be enough to show, that the ciphertext cannot be random, if  $$\langle g \rangle \neq \langle C_1 \rangle \quad(\text{or $Z_1$, respectively})$$  But how can Eve check for this property efficiently? Can someone point me in the right direction here?    Edit: A real-world situation where this flaw occurred Can you make multiple "if" conditions in Python? How to disable a USB port in Windows (XP) and make it available only for charging? Solving $a \sin\theta + b \cos\theta = c$ Could someone help me with the steps for solving the below equation $$a \sin\theta + b \cos\theta = c$$ I know that the solution is $$\theta = \tan^{-1} \frac{c}{^+_-\sqrt{a^2 + b^2 - c^2}} - \tan^{-1} \frac{a}{b} $$ I just can't figure out the right steps to arrive at this solution. Can I leave South Africa before my 90 days expire, and return after a few days to stay for another 90 days? How many times can an Australian leave and re-enter South Africa (90 days at a time without a visa) in a year, and do they need to be out of the country for a certain period of time before they re-enter?  I want to be in South Africa for as long as I can, however as an Australian without a visa I can only stay for 90 days at a time. What I would like to do is simply leave South Africa and go to another country in Africa for a few days, before returning with a new 90 day allowance.    Is this possible, or must I wait a certain period before re-entering South Africa/is there a limit to the amount of times I can do this in one year?