Given a complete set of time and space-like geodesics plus knowledge of how these geodesics vary is this enough to determine the metric?
Given a set of curved geodesics in 2D space, is there a way to determine the geometrical shape of said space?
How can I grep in PDF files? Is there a way to search PDF files using grep, without converting to text first in Ubuntu? SSL password on apache2 restart I setup wildcard SSL certificate from Godaddy on Apache2. Whenever the server restarts it asks for the passphrase for the SSL certificate's private key.    What's the best way to remove this obstacle to restarts, because when logfile rotation restart occurs in the middle of the night, the server doesn't come back up, and I get an unhappy client call in the morning, as it is a shared server. How to copy files that have too long of a filepath in Windows? Everyone knows that Wolverine's adamantium claws are super-sharp — sharper than even a razor — and virtually indestructible. What puzzled me the first time I saw Wolverine is: how do the claws stay in his body?  As it is shown, Wolverine's flesh and skin are human in strength, but the healing factor makes it superhumanly durable and strong. Still, when Wolverine slashes something, or someone, extremely hard, dense, or thick (as he has to use great amount of force), the claws don't tear through his hand and leave his hand through the opposite side of the palm (because of the action having equal and opposite reaction). How do I set the page title? I know I could change the page title with drupal_set_title(t('Amy page title')), but when I try it in Drupal 8 I get the There is no such function error.  How can I change page title in Drupal 8? I want to search for what += means, but Google won't return any documents.  Also when I come across some PHP code I don't understand I can't search for the keywords as written.  How can I search for these special characters or include these special characters in a search. I'm looking for a library/method to parse an html file with more html specific features than generic xml parsing libraries. In version 5.2 of Apple's Pages app for OS X (Mavericks), how do I change the page layout? What does high credit utilization really mean? How to Sort Multi-dimensional Array by Value? Does Reincarnation allows skills to be passed into other classes I'm mainly asking this for Disgaea: Afternoon of Darkness, given I have enough Mana to reincarnate a character into 4 different types of Mages (Green, Blue, Red, Star), a Cleric and then a Warrior, would the Warrior have all the spells learned from the previous classes? How can I make realistic looking potions as handouts An integer $a \pmod m$ has inverse if and only if $\gcd(a,m)=1$? An integer $a \pmod m$ has inverse if and only if $\gcd(a,m)=1$?  Why is this? I tried understanding it from my notes but I don't get it.  A thorough explanation would be greatly welcome.  Thanks for all the answers so far. I think my biggest problem is understanding why $\gcd(a,m)\neq1 \Longrightarrow \not\exists a^{-1}$. How much time have the Straw Hats spent with each other? What is the difference between a[bc]d and a{b,c}d? Why do people use a{b,c}d when there is already a[bc]d? Use Objects.hash() or own hashCode() implementation? What are the best SEO practices when changing domain names? I'm using the Yoast SEO plugin on a WordPress site on a new, more memorable domain to replace an old static HTML site with no SEO. I've followed , set up 301 redirects from the old domain to the new one, and filed a change of address in the Google Search Console. However, after a few days, the old site still shows in search results, and is ranked higher than the new one if you google our company name.   And, if I try to set the preferred domain in the Google Search Console Site Settings for the new site, I see this in place of the options to prefer www/non-www/http/https:     Not all options are available because of a Change of Address request   related to this site.   I've read of some cases where this condition has lasted for .  Is there anything more I can do to fix this? Have I done something wrong, or do I just need to wait, and for how long? Headers Including Each Other in C++ I'm a C++ newbie, but I wasn't able to find the answer to this (most likely trivial) question online.  I am having some trouble compiling some code where two classes include each other.  To begin, should my #include statements go inside or outside of my macros?  In practice, this hasn't seemed to matter.  However, in this particular case, I am having trouble.  Putting the #include statements outside of the macros causes the compiler to recurse and gives me "#include nested too deeply" errors.  This seems to makes sense to me since neither class has been fully defined before #include has been invoked.  However, strangely, when I try to put them inside, I am unable to declare a type of one of the classes, for it is not recognized.  Here is, in essence, what I'm trying to compile:  A.h  #ifndef A_H_ #define A_H_  #include "B.h"  class A {     private:         B b;      public:         A() : b(*this) {} };  #endif /*A_H_*/   B.h  #ifndef B_H_ #define B_H_  #include "A.h"  class B {     private:             A&amp; a;      public:         B(A&amp; a) : a(a) {}  };  #endif /*B_H_*/   main.cpp  #include "A.h"  int main() {     A a; }   If it makes a difference, I am using g++ 4.3.2.  And just to be clear, in general, where should #include statements go?  I have always seen them go outside of the macros, but the scenario I described clearly seems to break this principle.  Thanks to any helpers in advance!  Please allow me to clarify my intent if I have made any silly mistakes! Following an earlier question ,  I would love to implement the  as suggested by Russell McMahon.   That way I could switch between 4AA batteries (1.2V*4 or 1.5V*4) and USB power. The battery voltage would nicely be regulated to 5V too. And the idea was to use the shutdown pin of the chip IF USB power is detected. The device also has to work when no batteries are present.  I am not too experienced with this, but I thought to connect the 5V from the USB to the SHUTDOWN pin from the LDO chip. Pitywise, the pin function is inverted, if SHUTDOWN is low, Vout from the LDO chip is low.  I am now considering using an XOR gate to make the thing work:         &ndash; Schematic created using   I would love to limit the amount of components, but the number of diodes is already high, and the whole thing feels a bit crafted   My questions:    Is there a better suitable chip (with an inverted shutdown pin) is there a better circuit (without voltage drop) to get this (I would prefer to get rid of D1, but then, the XOR has no desired operation) Evaluation of $\int\frac{1}{x^2.(x^4+1)^{\frac{3}{4}}}dx$