Check if an object already exists in Java ArrayList
How do I compare strings in Java?
Layers tab not showing Usually my layers tab appears in the area of the red circle, but I did something that changed it. I would like to know how to get it back. Thanks! As the question says, when should I upgrade my camera body? In particular, if I have a low- to mid-range body (A DSLR such as a Nikon D3200 or Nikon D5100, or Canon SL1 or T5, or a mirrorless camera such as a Panasonic GH3 or an Olympus E-PL6). How do I know when I need to upgrade?  I have a complement of "kit" lenses, such as an 18-55mm f3.5-5.6 and a 55-200mm f4-5.6. Maybe I've even added a 50mm 1.8 to the kit. Flash is only for indoors (right?) and I usually shoot outside, so that means I don't need an external flash.  I shoot photos of my family and friends whether out at the park or having a picnic, my kids sports practices and games, vacation photos, as well as some landscapes, flowers, and whatever else catches my eye. Pretty familiar territory. I'm not a professional and don't intend to become one. Regression for an outcome (ratio or fraction) between 0 and 1 I am thinking of building a model predicting a ratio $a/b$, where $a \le b$ and $a &gt; 0$ and $b &gt; 0$. So, the ratio would be between $0$ and $1$.  I could use linear regression, although it doesn't naturally limit to 0..1.  I have no reason to believe the relationship is linear, but of course it is often used anyway, as a simple first model.  I could use a logistic regression, although it is normally used to predict the probability of a two-state outcome, not to predict a continuous value from the range 0..1.  Knowing nothing more, would you use linear regression, logistic regression, or hidden option c? The site still thinks it's attached to Stack Overflow Var[A+B+C] = Var [A] + Var [B] + Var [C] I know that this relationship is correct when A,B and C are pairwise independent. However, I'm finding it difficult to calculate it.  Let's say that: Var [A] = Var [B] = Var [C] = 0.25. How can I prove that Var[A+B+C] = 0.75?  I started to work with the formula: Var[A+B+C] =E[(A+B+C)^2]−(E[A+B+C])^2 but I got stuck.  Thanks! A commutative ring is a field iff the only ideals are $(0)$ and $(1)$ Let $R$ be a commutative ring with identity. Show that $R$ is a field if and only if the only ideals of $R$ are $R$ itself and the zero ideal $(0)$.  I can't figure out where to start other that I need to prove some biconditional statement. Any help? Get Last Friday of Month in Java Why is it true that "I before E, except after C"? I almost hesitate to ask this, because it is hard to believe no one else asked it; but it isn't showing up in the "similar titles" list.  What is special about 'C' that switches the 'IE' immediately following it? Why would Mystique's DNA allow for Sentinels that can duplicate mutant powers? The future Sentinels in  are clearly shown adapting to powers thrown at them by copying them. Isn't that what Rogue's DNA would allow for, not Mystique's? Mystique can just change appearance, not copy powers ... right? So why would study of her mutant genes allow for the abilities of the future Sentinels? How to find fixed points for DES weak keys Scenario 1: A grimlock hits Alice with a Spiked Bone Club, dealing 5 bludgeoning damage, plus 2 piercing damage. Alice's HP was 12.   Using the optional Massive Damage rules on page 273 of the DMG, does this count as more than half the HP from a single source, or less than half, but twice?  Scenario 2: Assume the same grimlock hits Bob with the same attack, this time rolling 6 bludgeoning damage, plus 3 piercing damage. Bob's Max HP is 8, and he had 1 HP remaining before he was hit.  Using the Instant Death rules on page 197 of the PHB, does the character die, or are the two damage types tracked separately? Does the character have to make a death saving throw for the second part of the damage? How can I download an older version of OS X/macOS? Sometimes it's hard to search for older versions of macOS &amp; OS X  on the App Store.  This is an attempt to provide the canonical QA for this issue, as per the Meta QA -  I expect it to be modified over time to hopefully become a complete information resource.  How can I get any older version of a Mac OS to be able to run as a VM, or to reinstall on my Mac? Split file into multiple files based on pattern I have a large file that's a couple hundred lines long. This file is partitioned into many parts by a specific identifier, lets say 'ABC'. This line 'ABC' appears 6 times so I want 6 output files. I'm familiar with split and awk but can't seem to create a command line that will do what I've described, any ideas?  Here's an example  ABC line 1 line 2 line 3 ABC line 1 line 2 ABC line1   I'd like three files where ABC is the first line in the new file and it ends before the next ABC is encountered. I'm working through some old integrals and I found one that's interesting. I can't quite remember how it's proved, so if someone could set me off in the right direction, it would be really helpful. Thanks!   $\int_{\mathbb{R}} e^{-ax^2 + bx} dx = \sqrt{ \dfrac{\pi}{a}} e^{\frac{b^2}{4a}}$  I've tried change of variable, but I'm not sure this is the right approach. Does there exist a bijective $f:\mathbb{N} \to \mathbb{N}$ such that $\sum f(n)/n^2$ converges? We know that $\displaystyle\zeta(2)=\sum\limits_{n=1}^{\infty} \frac{1}{n^2} = \frac{\pi^2}{6}$ and it converges.        Does there exists a bijective map $f:\mathbb{N} \to \mathbb{N}$ such that the sum $$\sum\limits_{n=1}^{\infty} \frac{f(n)}{n^2}$$ converges.      If our $s=2$ was not fixed, then can we have a function such that $\displaystyle \zeta(s)=\sum\limits_{n=1}^{\infty} \frac{f(n)}{n^s}$ converges Proof that a sum of Bernoulli rvs has Binomial distribution Let $\{X_n, n \geq 1\}$ be iid Bernoulli random variables with $\Pr(X_1 = 1) = p = 1 - \Pr(X_1 = 0)$ and let $S_n = \sum\limits_{i=1}^n X_i$ be the number of successes in $n$ trials. Show $S_n$ has a binomial distribution by the following methods:  1.) Prove for $n\geq0,$ $1\leq{k}\leq{n+1}$  $$\Pr(S_{n+1} = k) = p\Pr(S_n = k - 1) + q\Pr(S_n = k)\text{ where }q = 1-p.$$  2.) Solve the recursion using generating functions.  For the first method, I think I need to use convolution of $n + 1$ Bernoulli rvs, but I cannot immediately see the progression. For the second method, I don't exactly understand how to proceed either. This is problem 1.2 from Resnick's Adventures in Stochastic Processes. Proving $\lim_{n\to\infty} a^{\frac{1}{n}}=1$ by definition of limit According to :     The electron has no known substructure. Hence, it is defined or assumed to be a point particle with a point charge and no spatial extent.   Does point particle mean the particle should not have a shape, surface area or volume?  But when I searched Google for the "electron shape" I got many results (like  and ) that says electrons are round in shape. Background - I am doing my PhD in atmospheric physics/photobiology.  Here is a scenario:   The experiments are complete - the results are far better than expected  Successfully got the computer program to work properly and have developed another Papers are published Much of the thesis is drafted   The light at the end of the tunnel is most definitely no longer an oncoming train.  But, at this stage, you just don't feel like working on the thesis, you do other things like cleaning, reading, watching movies - procrastination gets worse, and worse despite the submission deadline coming closer.     The procrastination resulting in more apathy towards the project, despite being fully aware of how much work has been put into the project, how much has been achieved and how little, comparatively, needs to be done.  What strategies are there to overcome this academic-apathy, particularly in this late stage of the thesis? How do you prove that $\sum\limits_{n=0}^{\infty}{2n \choose n}x^n=(1-4x)^{-1/2}$? I tried to identify the sum as a binomial series, but the $4$ and the $-1/2$ puzzle me. (This series arises in studying the first passage time of a simple random walk.)