Undefined symbols for architecture x86_64: using a structure defined in header file
What is an undefined reference/unresolved external symbol error and how do I fix it?
Render an InputText based on Selected Option In my VF page I have an apex:selectList with a List of Vendors (e.g. Alcatel,Cisco ec..), the last option is "Other".   When the user select "Other" an apex:inputText should be rendered  where he can writes the Vendor. I'm not able to render the inputText Field   My VF page:  &lt;apex:outputPanel id="vendor2"&gt; &lt;p&gt;&lt;b&gt; Vendor: &lt;/b&gt;&lt;/p&gt; &lt;apex:selectList value="{!vendor}" multiselect="False" size="1"&gt;     &lt;apex:actionSupport event="onchange" action="{!specifyVendor}" rerender="otherPanel"/&gt;     &lt;apex:selectOptions value="{!vendors}"/&gt; &lt;/apex:selectList&gt;&lt;p/&gt; &lt;/apex:outputPanel&gt; &lt;br/&gt; &lt;apex:outputPanel id="otherPanel"&gt;     &lt;apex:inputText value="{!otherVendor}" rendered="{!vendor=='Other'}"&gt; Other: &lt;/apex:inputText&gt; &lt;/apex:outputPanel&gt;     &lt;br/&gt;&lt;br/&gt;    The custom controller:      public with sharing class ExcelPageController {          public String vendor {get; set;}//Vendor Name         public String otherVendor {get; set;}//Vendor Name          public List&lt;SelectOption&gt; getVendors(){             System.debug('getVendors');                 List&lt;SelectOption&gt; options = new List&lt;SelectOption&gt;();             options.add(new SelectOption('Cisco','Cisco'));             options.add(new SelectOption('Alcatel','Alcatel'));             options.add(new SelectOption('Tibco','Tibco'));             options.add(new SelectOption('Other','Other'));             return options;         }     public PageReference specifyVendor(){         System.debug(vendor);         return null;     } } Given two functions $f$ and $g$, is there a formula for the Fourier transform of $f \circ g$ in terms of the Fourier transforms of $f$ and $g$ individually?  I know you can do this for the sum, the product and the convolution of two functions. But I haven't seen a formula for the composition of two functions. Prove $(a^2+b^2)(c^2+d^2)\ge (ac+bd)^2$ for all $a,b,c,d\in\mathbb{R}$. Prove $(a^2+b^2)(c^2+d^2)\ge (ac+bd)^2$ for all $a,b,c,d\in\mathbb{R}$.  So $(a^2+b^2)(c^2+d^2) = a^2c^2+a^2d^2+b^2c^2+b^2d^2$  and $(ac+bd)^2 = a^2c^2+2acbd+b^2d^2$  So the problem is reduced to proving that $a^2d^2+b^2c^2\ge2acbd$ but I am not sure how to show that Distance between footnote and the line above it Why do we need to discard one dummy variable? I have learned that, for creating a regression model, we have to take care of categorical variables by converting them into dummy variables. As an example, if, in our data set, there is a variable like location:   Location  ---------- Californian NY Florida   We have to convert them like:  1  0  0 0  1  0 0  0  1   However, it was suggested that we have to discard one dummy variable, no matter how many dummy variables are there.   Why do we need to discard one dummy variable? What uses are there for "placement new"? Spheres with csv file Does the Black Panther suit give extra speed? So in Civil War, the Black Panther suit seems to give the suit holder some extra speed, because the guy was running as fast as Bucky and Captain America.  So does it give extra speed? If so, how does that work? How can I execute a terminal command (like grep) from my Objective-C Cocoa application? Partition on sublists beginning with a certain marker elements Notation of the second derivative - Where does the d go? In school I was taught that we use $\frac{du}{dx}$ as a notation for the first derivative of a function $u(x)$. I was also told that we could use the $d$ just like any variable. After some time we were given the notation for the second derivative and it was explained as follows: $$ \frac{d(\frac{du}{dx})}{dx} = \frac{d^2 u}{dx^2} $$ What I do not get here is, if we can use the $d$ as any variable, I would get the following result: $$ \frac{d(\frac{du}{dx})}{dx} =\frac{ddu}{dx\,dx} = \frac{d^2 u}{d^2 x^2} $$ Apparently it is not the same as the notation we were given. A $d$ is missing. I have done some research on this and found some vague comments about &quot;There are reasons for that, but you do not need to know...&quot; or &quot;That is mainly a  notation issue, but you do not need to know further.&quot; So what I am asking for is: Is this really just a notation thing? If so, does this mean we can actually NOT use d like a variable? If not, where does the $d$ go? I found  related question, but it does not really answer my specific question. So I would not see it as a duplicate, but correct me if my search has not been sufficient and there indeed is a similar question out there already. YA book about a young powerful female caster attending a school that trains in magical arts and duels I read a young adult novel around the turn of the century. This story features a young female protagonist that is very naturally gifted in magic. She is attending a  to learn mastery and control over her gifts.  A lot of her school revolves around magic dueling. The participants are taught to extend their inner aura like a second magical skin, possibly referred to as creating a shield, or . The user can increase the strength of the shield by focusing harder on it, but doing so means you have less ability to be offensive. The amount of energy needed to create a shield was half the energy a foe would need to focus at you to break it.  Ex: Mage A and B are equally matched. Mage A focuses half his power into a shield. Mage B would then need to focus 100% of his power to break A’s shield.  Another aspect I remember is that when dueling, a school master would extend a personal shield on to one of the combatants as a sort of secondary shield that goes underneath the combatants. When one mage broke the others mages personal shield, the school masters shield protects the losers life from harm, and the breaker of the shield is declared the winner.  I distinctly remember one match in which the protagonist is having a duel with another strong student. She creates a wind storm around herself that picks up the sand from the arena floor and makes her impossible to see and thus makes it hard for her opponent to focus on her shield to break it. She then lashes out at her opponent with incredibly powerful strikes with the final strike being so hard it shatters the opponents shield and then breaks the school masters shield as well and stops just shy of killing her dueling partner.  Any assistance on this one? I think my daughter would love to read it. I would like to pause a render that I have started, with the intention of resuming it at a later time (but during the same Blender session).  How can I do this? I've got the following two tables (in MySQL): Phone_book +----+------+--------------+ | id | name | phone_number | +----+------+--------------+ | 1  | John | 111111111111 | +----+------+--------------+ | 2  | Jane | 222222222222 | +----+------+--------------+  Call +----+------+--------------+ | id | date | phone_number | +----+------+--------------+ | 1  | 0945 | 111111111111 | +----+------+--------------+ | 2  | 0950 | 222222222222 | +----+------+--------------+ | 3  | 1045 | 333333333333 | +----+------+--------------+  How do I find out which calls were made by people whose phone_number is not in the Phone_book? The desired output would be: Call +----+------+--------------+ | id | date | phone_number | +----+------+--------------+ | 3  | 1045 | 333333333333 | +----+------+--------------+ Do plugin files have to follow a specific convention to be "picked up" by WordPress? Movie featuring  space crew, murders, a forbidden door and ending with a revelation I searched wide and far and couldn't come up with a title for a movie I watched somewhere around the mid-90ies up to early 00's as a rerun in late-night television (in Germany, specifically on Vox; but I'm sure it was an American movie to begin with).  Basically, what I remember from the story revolves around a crew in a space station or maybe space ship of some sort. Some crew members murder other crew members and there is some kind of door they are not supposed/unable to go through. Late in the movie they do go through the door and I'm pretty sure one of the first views is a skeleton of a dead security guard. It turns out the whole thing was some kind of simulation gone wrong and they find themselves to be in a (nuclear?) wasteland. And that's pretty much the revelation/wrap-up of the movie, as I recall it.  I would be delighted if somebody had any idea what movie this could be :) Thanks!  EDIT: The whole movie was in color and I think it was feature-length, not just 45 mins. The Density of Clouds The derivation of the Hamilton-Jacobi equation using canonical transformations is typically done involving a type-2 generating function.  Is it possible to use a another type of generating function, namely type 1, 3 or 4? I have a PostgreSQL table. select * is very slow whereas select id is nice and quick. I think it may be that the size of the row is very large and it's taking a while to transport, or it may be some other factor. I need all of the fields (or nearly all of them), so selecting just a subset isn't a quick fix. Selecting the fields that I want is still slow. Here's my table schema minus the names: integer                  | not null default nextval('core_page_id_seq'::regclass) character varying(255)   | not null character varying(64)    | not null text                     | default '{}'::text character varying(255)   |  integer                  | not null default 0 text                     | default '{}'::text text                     |  timestamp with time zone |  integer                  |  timestamp with time zone |  integer                  |   The size of the text field may be any size. But still, no more than a few kilobytes in the worst case. Questions  Is there anything about this that screams 'crazy inefficient'? Is there a way to measure page size at the Postgres command-line to help me debug this? For every set $A$, the empty set is a subset of $A$. The empty set is a set. Therefore, the empty set has a cardinality $\geq 1\ldots$