I made a ram block device using 'rd' module. Afterward, I formatted it with ext4 filesystem. I ran fio benchmark towards the ramdisk. But the performance is extremely low in that it shows only around 100 mb/s. My kernel version is 5.4.0 and the OS is Ubuntu 18.04. Any ideas?
I know that RAM disks are fast, faster than any disk, but they lose their contents on a shutdown of the operating system. The capacity is limited to the RAM. Is there a useful implementation on a new 64-bit Windows 2008 server?
I have a MacBook Pro Retina (2015). After updating to OS Mojave, Bluetooth has stopped working. I get an error message that "No Bluetooth Hardware Found".  I have already tried to do the following:   Go to the /Library/Preferences and delete the com.apple.Bluetooth.plist file Successfully resetting SMC. (pressing Shift+ctrl+alt + power button) Removing the Bluetooth icon from the menu bar    None of the above solutions has worked for me. We had a rule check tonight that we couldn't answer. On the Pathfinder wiki I could only find info on natural 20s and 1s in regards to attack rolls and saves in combat.  Do they also apply to skill checks? How many "polygons" does my model have? I have my model and in the info bar its show this   May I need to know how many polygons it has, but  there is no option to find polygons. Verts, Edge and Faces nothing polygon option there. In the website its say that the upload limit is 400,000 polygons. I did not get over that limit or how many polygons my model has? Can I have my sudo/su password different from my desktop login password? Every Function in a Finite Field is a Polynomial Function From a bank of past master's exams I am going through:     Let $F$ be a finite field. Show that any function from $F$ to $F$ is a polynomial function.   I know that finite fields are fields of $p$ elements for $p$ prime [EDIT: It's actually $p^n$ for $p$ prime; see comment below]. Since I have $p$ choices for the $p$ elements to map to, then I have $p^p$ distinct functions. I think every function can be written in the form $f(x) = a_{p-1}x^{p-1} + \dots + a_0x^0$. For then given the values $f(0), f(1), \ldots f(p-1)$, I can solve for the coefficents by the linear system of equations  $$ a_0 + \sum_{i=1}^{p-1} n^i a_i = f(n).$$  This then gives me a $p-1 \times p-1$ square matrix over the field $\mathbb{F}_p$:  $$\left( \begin{array}{ccccc} 1&amp; 0 &amp; 0 &amp; \ldots &amp; 0 \\ 1&amp; 1 &amp; 1 &amp; \dots &amp; 1 \\ 1&amp; 2 &amp; 4 &amp; \dots &amp; 2^{p-1} \\ \vdots &amp; \vdots &amp; \vdots &amp; &amp; \vdots \\ 1 &amp; p-1 &amp; (p-1)^2 &amp; \dots &amp; (p-1)^{p-1} \end{array} \right) \left( \begin{array}{c} a_0 \\ a_1 \\ a_2 \\ \vdots \\ a_{p-1} \end{array}\right)  = \left( \begin{array}{c} f(0) \\ f(1) \\ f(2) \\ \vdots \\ f(p-1) \end{array} \right)$$  If I can show this matrix is invertible, then I can always find the $a_i$. But I am a bit stumped on how to show this (partially because I don't think I've ever done linear algebra in a vector space over a finite field). It does not seem easy to show linear independence, or nonzero determinant, or full row rank.    Alternatively (I just thought of this), can I show this is true by arguing that the map between the two sets (the set of polynomials of degree $p-1$; and the set of functions $F \to F$) is injective, and that it must be a bijection because the sets have the same cardinality $p^p$? Generalized RBF Kernels There is the notion of Generalized RBF Kernels, for example in "Towards Optimal Bag-of-Features for Object Categorization and Semantic Video Retrieval" from Jiang (1) or in formula (2.72) in  (2).  They define: Gen. RBF Kernel: $e^{-pd(x,y)}$, where (1) says d can be any distance function and (2) requires it to be a metric.  I now have been wondering for a long time: Is a function defined by $e^{-pd(x,y)}$ where d is a metric always a Mercer's Kernel? I think in (2) it sounds like it, but if it were true, not many people know of it, since they are still looking to prove that $e^{-EMD(x,y)}$ is a kernel, where EMD = Earth Mover's Distance, which is a metric.  If its not a Mercer's Kernel - do you know of any counter example? Sorting list based on values from another list Can a warlock use one of their Thirsting Blade attacks to grapple or shove? Solution af a system of 2 quadratic equations I have a system of two quadratic equations with unknowns $x$ and $y$:  $$a_{1 1} x y + a_{1 2} x^2 + a_{1 3} y^2 + a_{1 4} x + a_{1 5} y + a_{1 6} = 0,\\ a_{2 1} x y + a_{2 2} x^2 + a_{2 3} y^2 + a_{2 4} x + a_{2 5} y + a_{2 6} = 0,$$  where $a_{i j}$ are arbitrary scalars.  Is there an algebraic solution of the above system? How can I set default value in ActiveRecord?  I see a post from Pratik that describes an ugly, complicated chunk of code:   class Item &lt; ActiveRecord::Base     def initialize_with_defaults(attrs = nil, &amp;block)     initialize_without_defaults(attrs) do       setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless         !attrs.nil? &amp;&amp; attrs.keys.map(&amp;:to_s).include?(key.to_s) }       setter.call('scheduler_type', 'hotseat')       yield self if block_given?     end   end   alias_method_chain :initialize, :defaults end   I have seen the following examples googling around:    def initialize      super     self.status = ACTIVE unless self.status   end   and    def after_initialize      return unless new_record?     self.status = ACTIVE   end   I've also seen people put it in their migration, but I'd rather see it defined in the model code.  Is there a canonical way to set default value for fields in ActiveRecord model? How to tell M2Eclipse to install jar file as a maven dependency I can't distinguish the difference in meaning between these  two sentences.   It really doesn't matter.  It doesn't  really matter.    It seems that there is a nuanced difference, but I cannot see what this is. Does iTunes work (well) on Ubuntu? I need to render a model on a transparent background. The models have a light source so they should be casting a shadow on a surface (the XY plane). The purpose for this is to overlay the rendered images (out of blender) on an image of the actual surface, so I want to generate the render including a semi-transparent shadow.  I don´t have any problem rendering the models on transparent background, but I can not make a shadow appear. I tried adding a surface below the model so the shadow can fall on it, but now there's the problem of keeping the surface from rendering.  How can I render the shadow on a transparent background? Solve the equation $28^x = 19^y+87^z$ in integers Fix half-installed package I am getting error while using sudo apt-get upgrade stating:  dpkg: error processing libgfortran3:amd64 (--configure):   package libgfortran3:amd64 is not ready for configuration   cannot configure (current status `half-installed') Errors were encountered while processing:   libgfortran3:amd64 E: Sub-process /usr/bin/dpkg returned an error code (1)   It does not seem to block the installation/upgrade other applications. I believe this problem arose due to direct shutting down of my PC while the application was being upgraded.  How can I fix this? Let's say we have $2$ particles facing each other and each traveling (almost) at speed of light.    Let's say I'm sitting on #$1$ particle so in my point of view #$2$ particle's speed is (almost) $c+c=2c$, double light speed? Please say why I am incorrect :)    EDIT: About sitting me is just example, so in point of view of #1 particle, the second one moves at (almost) $c+c=2c$ speed? Why do first years cross the lake to get to the castle? It makes sense to keep them together, and to have them arrive in the Great Hall separately from the rest of the school for the Sorting. But why the boats? The lake crossing is dramatic, but inefficient - as we see in book 4 when Dennis Creevey falls in the lake during the storm.   Is there a canon (books/movies or JKR) explanation for why the first years come up from the train in boats instead of carriages? What *is* an Artificial Neural Network? Can matter be described as the result of the curvature of space, instead of vice versa? Can matter be described as the result of the curvature of space, rather than the curvature of space being the result of matter, and energy being the cause of the curvature of space?