Couldn't find an answer for this in the wiki. If the bounty I set to my question expires without any answers/replies, can I set a second bounty?
It's possible to offer and award bounties of reputation on questions.   What is a bounty? How can I find questions that have a bounty attached? How do I start a bounty? When can I start a bounty? Why is the system requiring me to choose a bounty amount that's higher than the minimum? Can I use Markdown formatting in the bounty remarks? Can I edit the remark? How long is the bounty period? How do I award a bounty? Can I award a bounty to my own answer? Can I award a bounty to an old answer? If I offer a bounty on someone else's question, can I award the bounty to their answer? After awarding the bounty, can I remove it or move it to another answer at a later time? What happens if there's no answer after the bounty period? What happens if I feel my question is still unanswered? What is automatic awarding? Are bounty awards exempt from the 200 points/day reputation limit? How does Community Wiki mode affect bounties? How does user deletion or post dissociation affect bounties? Can I award a bounty to an answer from a deleted user or one where the author was dissociated? Can I offer a second bounty after the first one has expired? Can I raise my bounty? What happens if a bounty question is closed or deleted? Why can't I vote to close or migrate a bounty question? What happens if I delete my account while I have an active bounty? Do I keep an awarded bounty when I delete my answer? What happens if a question where I awarded a bounty later gets deleted or migrated? Can I cancel my bounty? Can I affect / divide / share part of my bounty to two (or more) users? How many outstanding bounties can a single user have?      See also:  in the Help Center
In De Broglie's Explanation for Bohr's Quantization Condition, why do we not use 2πr = n λ/2, why do we use 2πr = n λ? In de Broglie's explanation for Bohr's quantization condition, why do we not use $2\pi r = n\lambda/2$, why do we use $2\pi r = n\lambda$?  We know that in waves on strings, for standing waves creation in a string between two rigid supports, we use "Length of String" $ = n \lambda/2$. Why do we not use a similar concept here? How to list all functions in a Python module? We often get questions on bicycles.stackexchange about fitting wider or narrower tires to bicycles. We have a large number of these with answers suiting the specific bike or style of bicycle in question, but I have been unable to find one that provides a generic answer covering off all things that need to be considered. For most bicycles, the answer is the same regardless of the specific style and sizes of tires in question.   This is intended as a canonical question that we can point closed questions to. Navigation bar overlapped by status bar For $q, p$ odd primes such that $p \neq q$, there is not primitive root modulo $pq$. Database design for products with bundles of products Are there integral solutions to the equation $x^2+y^2-z^2=1$? Writing conditional (if/then) statements into ArcGIS Field Calculator using Python Parser? I have gotten stuck on seemingly simple ArcGIS field calculator python expression.  I obtained a great answer to a another similar question a few years ago: . Now I need to populate a new field based on 6 ranges of values (bedrock depth).  My attempt at writing this expression is below:    I just need to populate the empty field "bedrockdp" using the ranges in the toc called brockdepmin.     Pre-Logic Script Code:  def !GRIDCODE! (value):     if value &gt;0 and value &lt; 50:         return "0 - 50 cm from the surface"     else:         return "n/a"   bedrockdep =  GRIDCODE (!bedrockdep!) Modular arithmetic: division, fractions, solving linear congruences I want to ask a question about modular arithmetic. I know, that modular multiplicative inverse exists only if modulo and integer are relatively prime. I want to know, are there any ways of division in modular arithmetic, if modulo and integer aren't relatively prime? I tried to find info about that, but failed. Raspberry Pi Jessie Wi-Fi doesn't work with multiple IPs on same network I would like to use two different static IP addresses for the same network with the same Wi-Fi dongle. I read in different forums that it's better to use /etc/network/interfaces instead of dhcpcd.conf for that purpose. So I changed the /etc/network/interfaces that way:  auto lo iface lo inet loopback  iface eth0 inet dhcp auto wlan0 allow-hotplug wlan0 iface wlan0 inet static     address 192.168.0.60     netmask 255.255.255.0     gateway 192.168.0.10     wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf auto wlan0:0 allow-hotplug wlan0:0 iface wlan0:0 inet static     address 192.168.0.61     netmask 255.255.255.0     wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf   The issue now is that for the most of the time I can't ping any member of the network. During the first 10 seconds, everything works fine and then I mostly don't get any connection.  ifconfig shows the following:  lo        Link encap:Lokale Schleife             inet Adresse:127.0.0.1  Maske:255.0.0.0           inet6-Adresse: ::1/128 Gültigkeitsbereich:Maschine           UP LOOPBACK RUNNING  MTU:65536  Metrik:1           RX packets:1237 errors:0 dropped:0 overruns:0 frame:0           TX packets:1237 errors:0 dropped:0 overruns:0 carrier:0           Kollisionen:0 Sendewarteschlangenlänge:1            RX bytes:100748 (98.3 KiB)  TX bytes:100748 (98.3 KiB)  wlan0     Link encap:Ethernet  Hardware Adresse b8:27:eb:a2:4b:72             inet Adresse:192.168.0.60  Bcast:192.168.0.255  Maske:255.255.255.0           inet6-Adresse: fe80::ba27:ebff:fea2:4b72/64 Gültigkeitsbereich:Verbindung           UP BROADCAST MULTICAST  MTU:1500  Metrik:1           RX packets:15498 errors:0 dropped:10634 overruns:0 frame:0           TX packets:5446 errors:0 dropped:0 overruns:0 carrier:0           Kollisionen:0 Sendewarteschlangenlänge:1000            RX bytes:5910381 (5.6 MiB)  TX bytes:722284 (705.3 KiB)  wlan0:0   Link encap:Ethernet  Hardware Adresse b8:27:eb:a2:4b:72             inet Adresse:192.168.0.61  Bcast:192.168.0.255  Maske:255.255.255.0           UP BROADCAST MULTICAST  MTU:1500  Metrik:1   and route -ne has the following output:    Ziel            Router          Genmask         Flags   MSS Fenster irtt Iface 0.0.0.0         192.168.0.10    0.0.0.0         UG        0 0          0 wlan0 192.168.0.0     0.0.0.0         255.255.255.0   U         0 0          0 wlan0   I also stoped dhcpcd, the IPs aren't in the dhcp IP pool of the router and with one static IP everything works fine  Does anyone have any clue what I did wrong? Blackboard bold variants for Greek letters It is common (or it used to be) to use a blackboard-bold variant of \mu to denote roots of unity in some mathematical papers.  However, despite searching (several times, periodically over several years) I have never been able to locate any package or technique that makes this possible, other than using Metafont or possibly hunting through the font definitions to see if it is something I can create a variant of (along the lines of the suggestions in Section 8 of the Comprehensive LaTeX symbol list).  Thus far, I haven't been sufficiently motivated to learn how to do any of this (although it probably would have resulted in a net time savings), and I feel like I cannot be the only person who would have tried.  Is anyone aware of an existing way to produce this character? Permissions of /Users keep changing back to drwxrwxrwx I am working on a proof about Dedekind cuts on the positive rational numbers. I have been stuck for a while on the following point and would appreciate any help.  Given $x\in \mathbb{Q}^+$ such that $x^2&lt;2$, how to find $y\in \mathbb{Q}^+$ such $y&gt;x$ and $y^2&lt;2$? Removal of lines with no more or fewer than 'N' fields? Command for creating a directory and navigating into it directly? Quite often I need to perform this two commands:  mkdir abc cd abc   I am curious whether there is a simple command (or an alias that I can create and use) to do it in one go, like  user@GROUP:~$ mdcd abc user@GROUP:~/abc$   Is this possible? "I think him to be about 50" or "I think he is about 50"? How to use measured step response to tune control system How does one use a measured step response to tune either a PID or convolution control scheme? Inspired by , I'm interested a more detailed explanation of how to implement a control system based on the measured step response.  I would not try to guess all the effects.  There are probably some non-obvious things going on, and you can't know all the parameters. I would measure the step response.  Find two pump settings that both result in the ball being within the measurable range within the tube.  Then have the controller suddenly switch from one setting to the other open loop.  Meanwhile measure what the ball does over time.  That is the step response.  You can take the derivative of that and get the impulse response.  From the impulse response you can predict the motion of the ball for any history of pump settings, assuming this is a linear system.  It is probably linear enough over the small range of settings to keep the ball within its normal range. You can use this as a simulation base to find the parameters for old fashioned PID control.  Or you can use the impulse response directly to do a convolution control.  You have to low pass filter the control input enough so that convolution kernel doesn't go negative unless your pump is actually reversible and can suck the ball back down.  How exactly does this work? ; I assume &quot;convolution control&quot; is the use of the pole-zero or transfer function, but don't see exactly how to get the parameters. RELATED:  * Fatal error: Call to undefined function add_action() - an untouched problem The question was asked many times in many ways, but unfortunately is not covered well in most of the answers. I'm having the same issue doing things using include-files.  In my TwentyFourteen child theme's functions.php I used:  require_once get_stylesheet_directory_uri() .'/admin-panel/theme-options.php';   And I'm using . I've used it in many of my projects, the same way mentioned here, without having the error. But recently I'm having the issue in several of my projects. If I take the code to functions.php then everything's fine. But it's occurring only when I'm trying to include/require external file.  I'm having the error:     Fatal error: Call to undefined function add_action() in C:\xampp\htdocs\project\wp-content\themes\my-theme\admin-panel\theme-options.php on line 2   In this case I'm having the error using a child theme (of T14). But even in one of my parent theme I'm facing the issue. But in the same environment my other projects are running well with all the includes and/or requires (where several add_action()s are defined). I'm having issues in ALL the add_action() calls, like CPT assigning, Custom Taxonomy assigning etc. But I'm successfully developing another two projects including external files from inc/ folder where all my CPTs are assigned and their meta boxes too.  I tried reinstalling WordPress, deactivating all my plugins, tried from Child Theme, tried only the same thing by modifying TwentyFifteen (applying default theme), tried require(), require_once(), include(), include, require_once, and require one after another with failure. And I'm using WP 4.1.1 in all the good and problematic installs.  Majority of the previous questions are answered with a simple line:     As the message says, you haven defined the function add_action() and yet you're trying to use it.   But,   how come (isn't it already defined by WordPress)? and why it's differing project to project in the same environment (How come it's out of the scope now only in particular project[s])? Physical meaning of this integral in $k$-space I am trying to solve an integral in $k$-space where I want to calculate the ratio of the average energy of an arbitrary electronic band ($E(k)=k^n)$ to the square of average group velocity of electrons($v_g   = k^{n-1})$ approximately in the form of this expression given by $$L=\frac{\frac{\sum_{\mathbf{k}}k^{n}}{\sum_{\mathbf{k}}1}}{\left(\frac{\sum_{\mathbf{k}}k^{n-1}}{\sum_{\mathbf{k}}1}\right)^2}\;.$$  Now, I want to do this for $d$-dimensions, so I convert this sum to integral.  $$L=\frac{\dfrac{\int_{0}^{k_f}k^{n} d^d k}{\int_{0}^{k_f}1d^d k}}{\left(\dfrac{\int_{0}^{k_f}k^{n-1}d^d k}{\int_{0}^{k_f}1d^d k}\right)^2}$$ where $d^dk  = \dfrac{d \pi^{d/2}}{\Gamma(\frac{d}{2}+1)}k^{d-1}dk$ is the volume element in $d$-dimensional space.  I want to get a simple expression for $L$ and how it depends with $k_f,n$ and $d$. any physical insight into this integral could also be helpful. How can I use pathauto to generate URLs for deeply nested vocabularies? I am generating breadcrumbs from URL arguments as described .  I have a vocabulary that looks like this:  Arts-> Performing-> Dancing-> Ballet  I want my url to look like this: arts/performing/dancing/ballet  Using the pathauto module, I can do this for taxonomy terms:  [term:parent]/[term:name]   Which, on the Ballet page, gives me the following; not what I want:  dancing/ballet    If I use parents instead of parent,  ([term:parents]/[term:name]); this is close but not quite:  arts-performing-dancing/ballet   How can I get from arts-performing-dancing to arts/performing/dancing?