DDOS and Blocking IP's
I am under DDoS. What can I do?
Why do shadows from the sun join each other when near enough? I was laying on my bed, reading a book when the sun shone through the windows on my left. I happened to look at the wall on my right and noticed this very strange effect. The shadow of my elbow, when near the pages of the book, joined up with the shadow of the book even though I wasn't physically touching it.   I have posted :The video seems to be the wrong way up, but you still get the idea of what is happening.  What is causing this? Some sort of optical illusion where the light gets bent?  Coincidentally, I have been wondering about a similar effect recently where if you focus your eye on a nearby object, say, your finger, objects behind it in the distance seem to get curved/distorted around the edge of your finger. It seems awfully related...  EDIT: I could see the bulge with my bare eyes to the same extent as in the video! The room was well light and the wall was indeed quite bright. How can you use optional parameters in C#? Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).  We're building a web API that's programmatically generated from a C# class. The class has method GetFooBar(int a, int b) and the API has a method GetFooBar taking query params like &amp;a=foo &amp;b=bar.   The classes needs to support optional parameters, which isn't supported in C# the language. What's the best approach? How is stock price determined? Is stock price determined only by the last trade that takes place?  For example, if a stock I own is trading at $3.42, and I place a Sell Limit order for $0.00, will the stock price temporarily dip to $0.00?  Likewise, if I place a Buy Limit order for $100.00 for a stock that is trading at $1.23, will the price spike to $100.00?  Is there some sort of "average price" that is reported on the stock ticker?  Thanks for your help in understanding this! random access file in java I have the following fields:   Inventory control (16 byte record)   Product ID code (int – 4 bytes) Quantity in stock (int – 4 bytes) Price (double – 8 bytes)    How do I create a fixed length random access file using the above lengths? I tried some examples online, but I either get an EOF exception or random address values when I try to access them.  I tried some more examples and couldn't understand the concept very well. I'm trying a project with it and will try to explore more on it.  Here is some example data. There might be holes in the data where No. in stock could be 23 == 023.            Quantity ID. No.   In Stock   Price  -------   --------   ------  1001       476      $28.35  1002       240      $32.56  1003       517      $51.27  1004       284      $23.75  1005       165      $32.25   Thanks for the help. Is there an upside down caret character? I have to maintain a large number of classic ASP pages, many of which have tabular data with no sort capabilities at all. Whatever order the original developer used in the database query is what you're stuck with.  I want to to tack on some basic sorting to a bunch of these pages, and I'm doing it all client side with javascript. I already have the basic script done to sort a given table on a given column in a given direction, and it works well as long as the table is limited by certain conventions we follow here.    What I want to do for the UI is just indicate sort direction with the caret character ( ^ ) and ... what?  Is there a special character that is the direct opposite of a caret?  The letter v won't quite cut it.  Alternatively, is there another character pairing I can use? I'm having trouble understanding how to access each individual result returned from a subquery. The picture shows the code which:   takes fields and objects chosen by a user and assigns them to String variables, the string vars are used to query a dynamic query string, the query string is feed into a database.query and the result is stored in an array I can individually access each of the query results from this array (parent object results),  But I have not been able to individually access the subquery results.   If I feed the subquery results into an array...something like:  SObject[] c = p.get(i).getSObjects(childO);   I still can't get to each individual child record per parent. I can only see all child records per each parent. I need to get to each child record per adult, so that I can roll up results.  Can anyone help?  // These strings will be populated dynamically from a VF page String parentO  = 'Account'; String parentF  = 'Products_Purchased__c'; String childO   = 'Opportunity';     if(childO  == 'Opportunity'){ childO = 'Opportunities'; } String childF   = 'Product_Type__c';  // create dynamic SOQL query string String query = 'SELECT id, (select ' +childF+ ' from ' +childO+') FROM ' +parentO;  // query and store 33 results in variable p SObject[] p = Database.query(query);  for(Integer i = 0; i &lt; p.size(); i++){     system.debug('Parent result from SOQL query: ' +p[i]);     if(p.get(i).getSObjects(childO) &lt;&gt; null){         system.debug('Child result(s) from SOQL query: ' +p.get(i).getSObjects(childO));         system.debug('Child field: ' +c.get(i).get(childF));     } } Rendering an animation the way 3D view looks How do I evaluate this integral $\int_0^\pi{\frac{{{x^2}}}{{\sqrt 5-2\cos x}}}\operatorname d\!x$? Show that $$\int\limits_0^\pi{\frac{{{x^2}}}{{\sqrt 5-2\cos x}}}\operatorname d\!x =\frac{{{\pi^3}}}{{15}}+2\pi \ln^2 \left({\frac{{1+\sqrt 5 }}{2}}\right).$$   I don't have any idea how to start, but . For $a\ge 0$ let's define $$I(a)=\int_{0}^{\pi}\ln\left(1-2a\cos x+a^2\right)dx.$$ Find explicit formula for $I(a)$.   My attempt: Let  $$\begin{align*} f_n(x) &amp;= \frac{\ln\left(1-2 \left(a+\frac{1}{n}\right)\cos x+\left(a+\frac{1}{n}\right)^2\right)-\ln\left(1-2a\cos x+a^2\right)}{\frac{1}{n}}\\ &amp;=\frac{\ln\left(\displaystyle\frac{1-2 \left(a+\frac{1}{n}\right)\cos x+\left(a+\frac{1}{n}\right)^2}{1-2a\cos x+a^2}\right)}{\frac{1}{n}}\\ &amp;=\frac{\ln\left(1+\dfrac{1}{n}\left(\displaystyle\frac{2a-2\cos x+\frac{1}{n}}{1-2a\cos x+a^2}\right)\right)}{\frac{1}{n}}. \end{align*}$$ Now it is easy to see that $f_n(x) \to \frac{2a-2\cos x}{1-2a\cos x+a^2}$ as $n \to \infty$. $|f_n(x)|\le \frac{2a+2}{(1-a)^2}$ RHS is integrable so $\lim_{n\to\infty}\int_0^\pi f_n(x)dx = \int_0^\pi \frac{2a-2\cos x}{1-2a\cos x+a^2} dx=I'(a)$. But  $$\int_0^\pi \frac{2a-2\cos x}{1-2a\cos x+a^2}=\int_0^\pi\left(1-\frac{(1-a)^2}{1-2a\cos x+a^2}\right)dx.$$ Consider $$\int_0^\pi\frac{dx}{1-2a\cos x+a^2}=\int_0^\infty\frac{\frac{dy}{1+t^2}}{1-2a\frac{1-t^2}{1+t^2}+a^2}=\int_0^\infty\frac{dt}{1+t^2-2a(1-t^2)+a^2(1+t^2)}=\int_0^\infty\frac{dt}{(1-a)^2+\left((1+a)t\right)^2}\stackrel{(*)}{=}\frac{1}{(1-a)^2}\int_0^\infty\frac{dt}{1+\left(\frac{1+a}{1-a}t\right)^2}=\frac{1}{(1-a)(1+a)}\int_0^\infty\frac{du}{1+u^2}=\frac{1}{(1-a)(1+a)}\frac{\pi}{2}.$$ So $$I'(a)=\frac{\pi}{2}\left(2-\frac{1-a}{1+a}\right)\Rightarrow I(a)=\frac{\pi}{2}\left(3a-2\ln\left(a+1\right)\right).$$  It looks too easy, is there any crucial lack?  $(*)$ — we have to check $a=1$ here by hand and actually consider $[0,1), (1,\infty)$ but result on these two intervals may differ only by constant - it may be important but in my opinion not crucial for this proof. How can time dilation be symmetric? Suppose we have two twins travelling away from each other, each twin moving at some speed $v$:    Twin $A$ observes twin $B$’s time to be dilated so his clock runs faster than twin $B$’s clock. But twin $B$ observes twin $A$’s time to be dilated so his clock runs faster than twin $A$’s clock. Each twin thinks their clock is running faster. How can this be? Isn’t this a paradox? Prove that $\frac{1}{a^3(b+c)}+\frac{1}{b^3(a+c)}+\frac{1}{c^3(a+b)}\ge \frac32$ $a,b,c$ are positive reals with $abc = 1$. Prove that    $$\frac{1}{a^3(b+c)}+\frac{1}{b^3(a+c)}+\frac{1}{c^3(a+b)}\ge \frac32$$   I try to use AM $\ge$ HM.  $$\frac{\dfrac{1}{a^3(b+c)}+\dfrac{1}{b^3(a+c)}+\dfrac{1}{c^3(a+b)}}3\ge \frac{3}{a^3(b+c)+b^3(a+c)+c^3(a+b)}$$ Then how I proceed. What happens if you call erase() on a map element while iterating from begin to end? In the following code I loop through a map and test if an element needs to be erased.  Is it safe to erase the element and keep iterating or do I need to collect the keys in another container and do a second loop to call the erase()?  map&lt;string, SerialdMsg::SerialFunction_t&gt;::iterator pm_it; for (pm_it = port_map.begin(); pm_it != port_map.end(); pm_it++) {     if (pm_it-&gt;second == delete_this_id) {         port_map.erase(pm_it-&gt;first);     } }   UPDATE: Of course, I then  which I didn't think would be related but answers my question. How run a .jar file with a double-click? I have a problem running .jar files by double-clicking them. When I go to the Properties dialogue I can't find Java--only Archive Manager in the list of programs. But java -jar somefile.jar opens the program. How to remove the URL from the printing page? I want to remove the URL that gets printed on the bottom of the page.   like:  yomari.com/.../main.php?sen_n   How can it be omitted or prevent from getting printed?  To be more specific, is there any way I can prevent the page URL, date and the page title being printed along, while printing the web page? Is it true that $(R\times S)[G]\cong R[G]\times S[G]$? How do the Chitauri "ships" propel themselves? In the 2012 The Avengers film, the Chitauri army arrives through the portal along with these big robot alien whale Chitauri dudes. Here's one chasing Iron Man:  These guys basically swim through the air like... giant robot alien whales. I don't see any means of propulsion. Other, more humanoid Chitauri soldiers fly around on things that seem to be mechanical &quot;speeders&quot; of sorts. What are these guys? Are they ships, creatures, or both? Is there an explanation anywhere in the Avengers universe for how they defy gravity and swim through the air? Are airlines in the EU obligated to provide water for passengers? I was just thinking that maybe if we have more Stack&nbsp;Exchange websites then each person would be a member of more different sites on average. Since the time a person can spend online on average is limited it means he will be spending less time on each website. But would this affect the quality of these websites? I'm not talking only about the quality answers given but also the number of answers given, the promptness. Won't these things go down?  I think that the rate of questions won't go down much because you need to know what you need to know. However, the average time a person spends browsing through these websites (and chances upon a question he can answer) would decrease. So are we creating too many different Stack&nbsp;Exchange sites? Cancellation of Direct Products Derivative (or differential) of symmetric square root of a matrix Let A be a square, symmetric, positive-definite matrix.  Let S be its symmetric square root found by a singular value decomposition.  Let vech() be the half-vectorization operator.  Is there a convenient expression for the derivative (or differential) of vech(S) with respect to vech(A)?  I know the expression for an inverse, which is sort of like a matrix version of the power rule.  Would this approach work for a symmetric square root as well (i.e., (1/2)S^(-1/2))?