Remove Occurance of character from String array
How do I compare strings in Java?
How can I hire a professor to answer my advanced technical questions in a niche area? In short, How does one go about hiring a professor or someone really well established in their field for a private tutoring session?  I tried looking online but can’t find much, mainly websites for tutors that are practitioners or “experts” as in with with n years of experience at best. This doesn’t cut it at my level as I am a researcher with a PhD and already have published papers on my topic.   However, I am very passionate about my subject and always looking to grow. So I do have questions, very technical (in my case computer science) and would happily pay a fee for consulting with a professor in the field.  Any advice? I have a definition:  \newcommand{\arnold}{Arnold Schwarzenegger}   When I refer to it by:  \arnold is a   it is rendered as:   Arnold Schwarzeneggeris a    In order to have a space in front of "is" I would need to write  \arnold\ is a   Is there some other shorter way? Why multiple PTR records in DNS is not recommended? I   that using multiple PTR records in a DNS configuration is not recommended.   However, the reasons are often vague, or not so obvious, naming:    "it can cause problems",  "can trigger bugs in programs expecting a single answer" : it's the software's problem then, isn't it?! "can make DNS answer packet too large" : isn't this fixed with ?   Are these good reasons? Do you know of any other (good) reasons? All this kinda looks like a "legacy fear"... I would like to use the sentence     He was 'over-eager' to implement his plan, leading to failure.   I am looking for a single word which expresses over-eagerness in a negative sense.  TIA Algebraic Proof that $\sum\limits_{i=0}^n \binom{n}{i}=2^n$ How to salt PBKDF2, when generating both an AES key and a HMAC key for Encrypt then MAC? When using Encrypt-then-MAC with AES and HMAC by password, and given 128 bits of payload with the ciphertext to store a random salt, which would be more secure:   Using PBKDF2 with then entire 128 bit random salt and generating 512 bits of derived data to split into a 256 bit AES Key and a 256 bit HMAC key.   or   Using PBKDF2 separately for each key using two 64 bits salts to generate a 256 bit AES Key and a 256 bit HMAC key.    or    Better option? How could it be that the entropy of gas is not infinite?  If we use the formula $S=k\ln(\Omega)$ we get infinity because there are an infinite number of possible situations (because there are infinite possibilities of position and momentum for each molecule). If H is a subgroup of a group G and K is a normal subgroup of G the show that K is a normal subgroup of HK. Note K is a normal subgroup of HK  I thought I could just prove K is a subset of HK and vice versa so as to prove it a normal subgroup but then how to do this I have no idea because I keep getting hk element again while trying to do so.  I just tried to implement the steps to find HK is a subgroup of G. Why doesn't my ~/.bash_profile work? I'm using Linux Mint. My login shell (cat /etc/passwd | grep myUserName) is bash.  After I start my graphical desktop environment and run a terminal emulator from it, I can see that .bash_profile is not sourced (environment vars that are exported in it are unset). But if I log in from a text console (ctrl+alt+F1) or manually run bash -l from the terminal emulator, .bash_profile works fine.  Am I wrong when I think that .bash_profile should be sourced when X starts and all export'ed vars should be available in the terminal, running from X?  P.S. Placing everything in .bashrc and sourcing it from .bash_profile is not good idea (): environment stuff should be sourced only once. Let $F$ be a field and $x\in F$. If $x=-x$ and $1\neq -1$, then $$0=\frac{x+x}{1+1}=\frac{1+1}{1+1}x=x.$$ This means that the statement in the title is true if and only if $1\neq -1$. But how do we know that $1\neq -1$ for an arbitary field? How does time work in The Matrix? This is a basic question on Box-Jenkins MA models. As I understand, an MA model is basically a linear regression of time-series values $Y$ against previous error terms $e_t,..., e_{t-n}$. That is, the observation $Y$ is first regressed against its previous values $Y_{t-1}, ..., Y_{t-n}$ and then one or more $Y - \hat{Y}$ values are used as the error terms for the MA model.  But how are the error terms calculated in an ARIMA(0, 0, 2) model? If the MA model is used without an autoregressive part and thus no estimated value, how can I possibly have an error term? Allow bounty to be set with reputation from another site? Is reusing old code for a new assignment considered self plagiarism? How to protect yourself if you consider it to be, and a group partner does not? I am taking a graduate machine learning course and am working with another student in the class on a final project. In his undergraduate studies, the other student wrote code that accomplished a similar task, and mentioned in our previous meeting that we would be able to leverage much of this code for our current project if we wanted to. I responded that I believe it would constitute textbook cheating and self-plagiarism, but the other student disagrees and believes that re-using the code would not constitute self-plagiarism because he himself wrote it, and it would be redundant to re-write what he had already done.  Now, the course instructors have made it clear that we are not allowed to use any external libraries to perform certain classes of algorithms for this project. This students' prior code would fall under this category of prohibited tools, but he claims that it doesn't qualify because he wrote the code himself (so it is not an "external library"). I believe this is hyperbole, but he disagrees. It is also worth mentioning that this code is licensed under an , though it is not widely used at all.  It has gotten to the point where I am uncomfortable going forward with the project by re-using his old code, and he does not want to do work on the project that he considers to be redundant. My worry is that if it turns out we're not allowed to reuse the code, then using it could cause us to fail the course and severely negatively affect our reputations. Even if we don't get caught, I personally feel that it would be unethical to copy-paste old code and present it as though it's fresh code for this current project.  I am unsure of how to proceed. I have tried reaching out to the professor of the course some time ago (she has been traveling for some conferences recently and will be for a while) but I have not heard back from her. Additionally, the course TAs have been unwilling to weigh-in on the situation.  I have the following questions:   Is the above situation usually considered to be self plagiarism? Why or why not? Is the above act typically allowed in an academic setting? Assuming you are in my position, and consider re-using the code to be cheating and/or unethical, what is the best way to proceed; both in terms of how to make progress on the project, how to compromise with my group mate, and how to protect myself if my group mate refuses to budge. The weighted sum of two independent Poisson random variables Using wikipedia I found a way to calculate the probability mass function resulting from the sum of two Poisson random variables. However, I think that the approach I have is wrong.  Let $X_1, X_2$ be two independent Poisson random variables with mean $\lambda_1, \lambda_2$, and $S_2 =  a_1 X_1+a_2 X_2$, where the $a_1$ and $a_2$ are constants, then the probability-generating function of $S_2$ is given by $$ G_{S_2}(z) = \operatorname{E}(z^{S_2})= \operatorname{E}(z^{a_1 X_1+a_2 X_2}) G_{X_1}(z^{a_1})G_{X_2}(z^{a_2}). $$ Now, using the fact that the probability-generating function for a Poisson random variable is $G_{X_i}(z) = \textrm{e}^{\lambda_i(z - 1)}$, we can write the probability-generating function of the sum of the two independent Poisson random variables as $$ \begin{aligned} G_{S_2}(z) &amp;= \textrm{e}^{\lambda_1(z^{a_1} - 1)}\textrm{e}^{\lambda_2(z^{a_2} - 1)}  \\ &amp;= \textrm{e}^{\lambda_1(z^{a_1} - 1)+\lambda_2(z^{a_2} - 1)}. \end{aligned} $$ It seems that the probability mass function of $S_2$ is recovered by taking derivatives of $G_{S_2}(z)$ $\operatorname{Pr}(S_2 = k) = \frac{G_{S_2}^{(k)}(0)}{k!}$, where $G_{S_2}^{(k)} = \frac{d^k G_{S_2}(z)}{ d z^k}$.  Is this is correct? I have the feeling I cannot just take the derivative to obtain the probability mass function, because of the constants $a_1$ and $a_2$. Is this right? Is there an alternative approach?  If this is correct can I now obtain an approximation of the cumulative distribution by truncating the infinite sum over all k? Using equations to draw out complex objects How do people come up with equations of curves to draw out complex objects?  Some popular examples would include:  &amp;  .  This  explains the rationale for the batman curve nicely.  But other than trial and error, I can't see a reasonable way of drawing the much more complicated PSY curve. normal subgroups of Alternating group Klein's $4$ group, $\{1\}$ and $A_4$ are three normal subgroups of $A_4$. I want to know about any other normal subgroups of $A_4$. Do these exist? I'm usually running many different StackExchange sites in Firefox using tabs (using ReloadEvery to update every 5 minutes).  Right now to check for activity, I have to manually click on the tab to see if the envelope is lighted.  How about making the icon on the tab i.e. the title text change in some way, denoting that you have activity on the page?  We already add a message count for the chat tabs, so this shouldn't be very complicated.  Possible Example: I've tried multiple times to  import a SVG file from illustrator CS5.5 to Blender 2.71 and 2.73. However, I do not see a mesh, curve, or anything pop up in my "Outliner" window. So I know its not so small I can't see it. I even made sure under user preferences that the "import and export of SVG 1.1 format" is "checked." I've tried even just importing text from illustrator and I'm still getting no where. What can I do to resolve this problem? If this is common error with this version of Blender, then what can I do to transform an image into a 3D object in Blender? How do I get started working with JSON in Apex? This is a canonical question and answer developed by the community to help address common questions. If you've been directed here, or your question has been closed as a duplicate, please look through the resources here and use them to shape more specific questions. To browse all canonical questions and answers, navigate to the  tag.  This question and answer is owned by the community! If you can improve it and make it more useful, you're welcome to edit it.  I have a specific JSON structure in mind. I need to either deserialize this structure that's coming in from a web service, or I need to serialize data into this structure to transmit it to another system. How should I get started on this project in Apex?