Search Results

Search found 1011 results on 41 pages for 'linear algebra'.

Page 27/41 | < Previous Page | 23 24 25 26 27 28 29 30 31 32 33 34  | Next Page >

• Is there really such a thing as "being good at math"?

  - by thezhaba

  Aside from gifted individuals able to perform complex calculations in their head, I'm wondering if proficiency in mathematics, namely calculus and algebra, has really got to do with one's natural inclination towards sciences, if you can put it that way. A number of students in my calculus course pick up material in seemingly no time whereas I, personally, have to spend time thinking about and understanding most concepts. Even then, if a question that requires a bit more 'imagination' comes up I don't always recognize the concepts behind it, as is the case with calculus proofs, for instance. Nevertheless, I refuse to believe that I'm simply not made for it. I do very well in programming and software engineering courses where a lot of students struggle. At first I could not grasp what they found to be so difficult, but eventually I realized that having previous programming experience is a great asset -- once I've seen and made practical use of the programming concepts learning about them in depth in an academic setting became much easier as I have then already seen their use "in the wild". I suppose I'm hoping that something similar happens with mathematics -- perhaps once the practical idea behind a concept (which authors of textbooks sure do a great job of concealing..) is evident, understanding the seemingly dry and symbolic ideas and proofs would be more obvious? I'm really not sure. All I'm sure of is I'd like to get better at calculus, but I don't yet understand why some of us pick it up easily while others have to spend considerable amounts of time on it and still not have complete understanding if an unusual problem is given.

  Read the article

• Can Haskell's monads be thought of as using and returning a hidden state parameter?

  - by AJM

  I don't understand the exact algebra and theory behind Haskell's monads. However, when I think about functional programming in general I get the impression that state would be modelled by taking an initial state and generating a copy of it to represent the next state. This is like when one list is appended to another; neither list gets modified, but a third list is created and returned. Is it therefore valid to think of monadic operations as implicitly taking an initial state object as a parameter and implicitly returning a final state object? These state objects would be hidden so that the programmer doesn't have to worry about them and to control how they gets accessed. So, the programmer would not try to copy the object representing the IO stream as it was ten minutes ago. In other words, if we have this code: main = do putStrLn "Enter your name:" name <- getLine putStrLn ( "Hello " ++ name ) ...is it OK to think of the IO monad and the "do" syntax as representing this style of code? putStrLn :: IOState -> String -> IOState getLine :: IOState -> (IOState, String) main :: IOState -> IOState -- main returns an IOState we can call "state3" main state0 = putStrLn state2 ("Hello " ++ name) where (state2, name) = getLine state1 state1 = putStrLn state0 "Enter your name:"

  Read the article

• How do I become better in math, after being a programmer for several years.

  - by loxs

  I've had quite a weird career till now. First I graduated from a medical school. Then I went into marketing (pharmaceuticals). And then umm, after some time, I decided to go for my (till then) hobby and became a "professional" programmer. I've been quite successful at this ever since. I have quite some languages "under my belt". I earn not bad and I have been involved in the opensource community quite heavily. The thing is that I suck at math :). Well, not totally of course, as I get my work done. But I don't know how much I suck. And I don't know how to find out. Math has never really been of any priority during my middle/high school years. I only picked as little as I could afford, because I was always getting ready to go for Medicine. Of course I know the basics of algebra. Things like "normal" and square equations. Also the basics of geometry. But well, there are things that I have missed. And lately I am being fascinated by things like probability theory, infinity, chaos/order etc. But every time I try to learn something about these topics, I hit a wall of terminology, special symbols, and some special kind of thinking, that is quite like mine (a programmer), but also a lot different (and appears weird to me). So, what kinds of books would you recommend me? It's very hard to find something suitable. All that I find are either too easy (and boring) or totally impenetrable.

  Read the article

• Interesting Scala typing solution, doesn't work in 2.7.7?

  - by djc

  I'm trying to build some image algebra code that can work with images (basically a linear pixel buffer + dimensions) that have different types for the pixel. To get this to work, I've defined a parametrized Pixel trait with a few methods that should be able to get used with any Pixel subclass. (For now, I'm only interested in operations that work on the same Pixel type.) Here it is: trait Pixel[T <: Pixel[T]] { def mul(v: Double): T def max(v: T): T def div(v: Double): T def div(v: T): T } Now I define a single Pixel type that has storage based on three doubles (basically RGB 0.0-1.0), I've called it TripleDoublePixel: class TripleDoublePixel(v: Array[Double]) extends Pixel[TripleDoublePixel] { var data: Array[Double] = v def this() = this(Array(0.0, 0.0, 0.0)) def toString(): String = { "(" + data(0) + ", " + data(1) + ", " + data(2) + ")" } def increment(v: TripleDoublePixel) { data(0) += v.data(0) data(1) += v.data(1) data(2) += v.data(2) } def mul(v: Double): TripleDoublePixel = { new TripleDoublePixel(data.map(x => x * v)) } def div(v: Double): TripleDoublePixel = { new TripleDoublePixel(data.map(x => x / v)) } def div(v: TripleDoublePixel): TripleDoublePixel = { var tmp = new Array[Double](3) tmp(0) = data(0) / v.data(0) tmp(1) = data(1) / v.data(1) tmp(2) = data(2) / v.data(2) new TripleDoublePixel(tmp) } def max(v: TripleDoublePixel): TripleDoublePixel = { val lv = data(0) * data(0) + data(1) * data(1) + data(2) * data(2) val vv = v.data(0) * v.data(0) + v.data(1) * v.data(1) + v.data(2) * v.data(2) if (lv > vv) (this) else v } } Now I want to write code to use this, that doesn't have to know what type the pixels are. For example: def idiv[T](a: Image[T], b: Image[T]) { for (i <- 0 until a.data.size) { a.data(i) = a.data(i).div(b.data(i)) } } Unfortunately, this doesn't compile: (fragment of lindet-gen.scala):145: error: value div is not a member of T a.data(i) = a.data(i).div(b.data(i)) I was told in #scala that this worked for someone else, but that was on 2.8. I've tried to get 2.8-rc1 going, but it doesn't compile for me. Is there any way to get this to work in 2.7.7?

  Read the article

• R Random Data Sets within loops

  - by jugossery

  Here is what I want to do: I have a time series data frame with let us say 100 time-series of length 600 - each in one column of the data frame. I want to pick up 4 of the time-series randomly and then assign them random weights that sum up to one (ie 0.1, 0.5, 0.3, 0.1). Using those I want to compute the mean of the sum of the 4 weighted time series variables (e.g. convex combination). I want to do this let us say 100k times and store each result in the form ts1.name, ts2.name, ts3.name, ts4.name, weight1, weight2, weight3, weight4, mean so that I get a 9*100k df. I tried some things already but R is very bad with loops and I know vector oriented solutions are better because of R design. Thanks Here is what I did and I know it is horrible The df is in the form v1,v2,v2.....v100 1,5,6,.......9 2,4,6,.......10 3,5,8,.......6 2,2,8,.......2 etc e=NULL for (x in 1:100000) { s=sample(1:100,4)#pick 4 variables randomly a=sample(seq(0,1,0.01),1) b=sample(seq(0,1-a,0.01),1) c=sample(seq(0,(1-a-b),0.01),1) d=1-a-b-c e=c(a,b,c,d)#4 random weights average=mean(timeseries.df[,s]%*%t(e)) e=rbind(e,s,average)#in the end i get the 9*100k df } The procedure runs way to slow. EDIT: Thanks for the help i had,i am not used to think R and i am not very used to translate every problem into a matrix algebra equation which is what you need in R. Then the problem becomes a little bit complex if i want to calculate the standard deviation. i need the covariance matrix and i am not sure i can if/how i can pick random elements for each sample from the original timeseries.df covariance matrix then compute the sample variance (t(sampleweights)%*%sample_cov.mat%*%sampleweights) to get in the end the ts.weighted_standard_dev matrix Last question what is the best way to proceed if i want to bootstrap the original df x times and then apply the same computations to test the robustness of my datas thanks

  Read the article

• Android page Curl animation

  - by Meymann

  Hi... Two questions: Is there a simple way to do the Curl page flipping animation? A Curl animation is animation of pages flipping, including the page above rolling and the shadows over the lower page. What is the recommended way to do a "gallery" that displays two pages at a time (just like a book)? Is it: Letting the adapter display a linear layout of two images at a time? (it won't let me show a page flipping over the other like a book) Using two pages, placing somehow one near the other, and then when it's time to animate -move the next two pages over? What is the better way that would enable displaying the left page flipping over the right page? Thanks Meymann

  Read the article

• Java: ArrayList bottleneck

  - by Jack

  Hello, while profiling a java application that calculates hierarchical clustering of thousands of elements I realized that ArrayList.get occupies like half of the CPU needed in the clusterization part of the execution. The algorithm searches the two more similar elements (so it is O(n*(n+1)/2) ), here's the pseudo code: int currentMax = 0.0f for (int i = 0 to n) for (int j = i to n) get content i-th and j-th if their similarity > currentMax update currentMax merge the two clusters So effectively there are a lot of ArrayList.get involved. Is there a faster way? I though that since ArrayList should be a linear array of references it should be the quickest way and maybe I can't do anything since there are simple too many gets.. but maybe I'm wrong. I don't think using a HashMap could work since I need to get them all on every iteration and map.values() should be backed by an ArrayList anyway.. Otherwise should I try other collection libraries that are more optimized? Like google's one, or apache one.. Thanks

  Read the article

• Android: Changing LinearLayout in a widget.

  - by Profete162

  Hello all, I have this really annoying problem: In my widget, i would like to change the background by code. I noticed on the Google doc than I can easily change the background of an Imageview: remoteViews.setImageViewResource(R.id.my_iv, R.drawable.my_bg); Ok, too easy, i want to change now the Linear layout.. What I read about the remoteview id that I can change a Bitmap, Int, Bool, String, etc... but not a drawable. So i guess i cannot use: remoteViews.setBitmap(R.id.my_ll,"setBackgroundDrawable",BitmapFactory.decodeResource(context.getResources(), R.drawablemy_bg)); I am totally disapointed and tried a last idea: views.setInt(R.id.my_ll,"setBackgroundResource",R.drawable.my_bg); But The logcat told me: android.widget.RemoteViews$ActionException:view: android.widget.LinearLayout can't use method with RemoteViews: setBackgroundResource(int) I am totally lost and I really don't know what to do... I would really appreciate any help. Thank a lot!

  Read the article

• How to get image to pulse with opacity with JQuery

  - by Alex

  I am trying to get an image to change opacity smoothly over a duration of time. Here's the code I have for it. <script type="text/javascript"> pulsem(elementid){ var element = document.getElementById(elementid) jquery(element).pulse({opacity: [0,1]}, { duration: 100, // duration of EACH individual animation times: 3, // Will go three times through the pulse array [0,1] easing: 'linear', // easing function for each individual animation complete: function() { alert("I'm done pulsing!"); } }) </script> <a href="city.htm"><img src="waterloo.png" onmouseover="javascript:pulsem("waterloo")" border="0" class="env" id="waterloo"/></a> Also, is there a way for this to happen automatically without the need of a mouseover? Thanks.

  Read the article

• Multithreading/Parallel Processing in PHP

  - by manyxcxi

  I have a PHP script that will generate a report using PHPExcel from data queried from a MySQL DB. Currently, it is linear in processing in that it gets the data back from MySQL, reads in the Excel template, writes the data to the template, then outputs it. I have optimized the code to the point that the data is only iterated over once, and there is very little processing done on the PHP side. The query returns hundreds of lines in less than .001 seconds, so it is running fast enough. After some timing I have found my bottlenecks to be (surprise, surprise) reading the template and writing the output. I would like to do this: Spawn a thread/process to read the template Spawn a thread/process to fetch the data Return back to parent thread - Parent thread will wait until both are complete Proceed on as normal My main questions are is this possible, is it worth it? If yes to both, how would you tackle it? Also, it is PHP 5 on CentOS

  Read the article

• Error when trying to create a faceted plot in ggplot2

  - by John Horton

  I am trying to make a faceted plot in ggplot2 of the coefficients on the regressors from two linear models with the same predictors. The data frame I constructed is this: r.together> reg coef se y 1 (Intercept) 5.068608671 0.6990873 Labels 2 goodTRUE 0.310575129 0.5228815 Labels 3 indiaTRUE -1.196868662 0.5192330 Labels 4 moneyTRUE -0.586451273 0.6011257 Labels 5 maleTRUE -0.157618168 0.5332040 Labels 6 (Intercept) 4.225580743 0.6010509 Bonus 7 goodTRUE 1.272760149 0.4524954 Bonus 8 indiaTRUE -0.829588862 0.4492838 Bonus 9 moneyTRUE -0.003571476 0.5175601 Bonus 10 maleTRUE 0.977011737 0.4602726 Bonus The "y" column is a label for the model, reg are the regressors and coef and se are what you would think. I want to plot: g <- qplot(reg, coef, facets=.~y, data = r.together) + coord_flip() But when I try to display the plot, I get: > print(g) Error in names(df) <- output : 'names' attribute [2] must be the same length as the vector [1] What's strange is that qplot(reg, coef, colour=y, data = r.together) + coord_flip() plots as you would expect.

  Read the article

• Calculating determinant by hand

  - by ldigas

  Okey, this is only half programming, but let's see how you are on terms with manual calculations. I believe many of you did this on your university's while giving "linear systems" ... the problem is it's been so long I can't remember how to do it any more. I know quite a few algorithms for calculating determinants, and they all work fine ... for large systems, where one would never try to do it manually. Unfortunatelly, I'm soon going on an exam, where I do have to calculate it manually, up to the system of 5. So, I have a K(omega) matrix that looks like this: [2-(omega^2)*c -4 2 0 0] [-2 5-(omega^2)*c -4 1 0] [1 -4 6-(omega^2)*c -4 1] [0 1 -4 5-(omega^2)*c -2] [0 0 2 -4 2-(omega^2)*c] and I need all the omegas which satisfy the det[K(omega)]=0 criteria. What would be a good way to calculate it so it can be repeated in a manual process ?

  Read the article

• Adding audio channel using ffmpeg

  - by Raj

  Hi all, I am working on ffmpeg and trying to add a audio stream on the fly. I am using AudioQueues and I get raw audio buffer. I am encoding audio with linear PCM and hence the audio I get will be of raw format, which I know ffmpeg does accept it. But I cannot figure out how. I have looked into AVStream, where in we have to create a new stream for this audio channel but how do I encode it to a video which is already initialized in another AVStream structure. Overall, I would like to have an idea of the architecture of ffmpeg. I found it difficult to work since it is least documented. Any pointers or details are appreciated. Thanks and Regards, Raj Pawan G

  Read the article

• Understanding glm$residuals and resid(glm)

  - by Michael Bishop

  Hi, Can you tell me what is returned by glm$residuals and resid(glm) where glm is a quasipoisson object. e.g. How would I create them using glm$y and glm$linear.predictors. glm$residuals n missing unique Mean .05 .10 .25 .50 .75 .90 .95 37715 10042 2174 -0.2574 -2.7538 -2.2661 -1.4480 -0.4381 0.7542 1.9845 2.7749 lowest : -4.243 -3.552 -3.509 -3.481 -3.464 highest: 8.195 8.319 8.592 9.089 9.416 resid(glm) n missing unique Mean .05 .10 .25 37715 0 2048 -2.727e-10 -1.0000 -1.0000 -0.6276 .50 .75 .90 .95 -0.2080 0.4106 1.1766 1.7333 lowest : -1.0000 -0.8415 -0.8350 -0.8333 -0.8288 highest: 7.2491 7.6110 7.6486 7.9574 10.1932

  Read the article

• JQuery preventDefault() but still add the fragment path to the URL without navigating to the fragment

  - by jdln

  My question is similar to this one but none of the answers solve my problem: Use JQuery preventDefault(), but still add the path to the URL When a user clicks a fragment link, I need to remove the default behaviour of jumping to the fragment but still add the fragment to the URL. This code (taken from the link) will fire the animation, and then add the fragment to the URL. However the fragment is then navigated to, which im my case breaks my site. $("#login_link").click(function (e) { e.preventDefault(); $("#login").animate({ 'margin-top': 0 }, 600, 'linear', function(){ window.location.hash = $(this).attr('href'); }); });

  Read the article

• How to sketch out an event-driven system?

  - by Jordan

  I'm trying to design a system in Node.js (an attempt at solving one of my earlier problems, using Node's concurrency) but I'm running into trouble figuring out how to draw a plan of how the thing should operate. I'm getting very tripped up thinking in terms of callbacks instead of returned values. The flow isn't linear, and it's really boggling my ability to draft it. How does one draw out an operational flow for an event-driven system? I need something I can look at and say "Ok, yes, that's how it will work. I'll start it over here, and it will give me back these results over here." Pictures would be very helpful for this one. Thanks. Edit: I'm looking for something more granular than UML, specifically, something that will help me transition from a blocking and object-oriented programming structure, where I'm comfortable, to a non-blocking and event driven structure, where I'm unfamiliar.

  Read the article

• marquee text view in android

  - by raqz

  i tried various combinations as answered here in SO...but i am still not able to get the text to marquee... combination 1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:id="@+id/organizationText" android:layout_height="38px" android:gravity="center_horizontal" android:textColor="#0099CC" android:layout_gravity="center" android:textSize="08pt" android:layout_width="wrap_content" android:maxLines="1" android:ellipsize="marquee" android:fadingEdge="horizontal" android:marqueeRepeatLimit="marquee_forever" android:scrollHorizontally="true" android:focusable="true" android:focusableInTouchMode="true" /> </RelativeLayout> orgText.setSelected(true); orgText.setEllipsize(TruncateAt.MARQUEE); orgText.setText(organization); I tried without using setSelected but it still doesnt work. any help would be appreciated... also, this entire view is a part of Linear layout.

  Read the article

• How does the linux kernel manage less than 1GB physical memory ?

  - by TheLoneJoker

  I'm learning the linux kernel internals and while reading "Understanding Linux Kernel", quite a few memory related questions struck me. One of them is, how the Linux kernel handles the memory mapping if the physical memory of say only 512 MB is installed on my system. As I read, kernel maps 0(or 16) MB-896MB physical RAM into 0xC0000000 linear address and can directly address it. So, in the above described case where I only have 512 MB: How can the kernel map 896 MB from only 512 MB ? What about user mode processes in this situation? Where are user mode processes in phys RAM? Every article explains only the situation, when you've installed 4 GB of memory and the kernel maps the 1 GB into kernel space and user processes uses the remaining amount of RAM. I would appreciate any help in improving my understanding. Thanks..!

  Read the article

• How to place a Linearlayout at bottom inside a Relativelayout in android

  - by SANDHYA

  I need to place a linear layout at bottom inside a relativelayout which is the top most parent in xml. How can i do this? Please help me. <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/background" android:orientation="vertical" > <RelativeLayout ....... <<--- this should occupy total available space </Relativelayout <Linearlayout ....... <<-- this should place at bottom always with height 50dp </LineaLayout> </ReltiveLayout>

  Read the article

• Send files using Content-Disposition: attachment in parallel

  - by Manos Dilaverakis

  I have a PHP page that sends a file to the browser depending on the request data it receives. getfile.php?get=something sends file A, getfile.php?get=somethingelse sends file B and so on and so forth. This is done like so: header('Content-Disposition: attachment; filename='. urlencode($filename)); readfile($fileURL); It works except it can only send one file at a time. Any other files requested are send in linear fashion. One starts as soon as another finishes. How can I get this to send files in parallel if the user requests another file while one is downloading?

  Read the article

• Algorithm to generate radial gradient

  - by user146780

  I have this algorithm here: pc = # the point you are coloring now p0 = # start point p1 = # end point v = p1 - p0 d = Length(v) v = Normalize(v) # or Scale(v, 1/d) v0 = pc - p0 t = Dot(v0, v) t = Clamp(t/d, 0, 1) color = (start_color * t) + (end_color * (1 - t)) to generate point to point linear gradients. It works very well for me. I was wondering if there was a similar algorithm to generate radial gradients. By similar, I mean one that solves for color at point P rather than solve for P at a certain color (where P is the coordinate you are painting). Thanks

  Read the article

• Is the heap actually a heap?

  - by ElectricDialect

  In .NET (and Java as far as I know), the area where objects are dynamically allocated is referred to as the managed heap. However, most documentation that describes how the managed heap works depicts it as a linear data structure, such as a linked list or stack. So, is the managed heap actually a heap, or is it implemented with some other data structure? If it actually does not use a heap data structure, is seems like a significant failure of terminology to overload the meaning of this word. If it is in fact a heap data structure, what is the value that satisfies the heap property: the size of the allocated memory region?

  Read the article

• Producer/consumer in Grails?

  - by Mulone

  Hi all, I'm trying to implement a Consumer/Producer app in Grails, after several unsuccessful attempts at implementing concurrent threads. Basically I want to store all the events coming from a clients (through separate AJAX calls) in a single queue and then process such a queue in a linear way as soon as new events are added. This looks like a Producer/Consumer problem: http://en.wikipedia.org/wiki/Producer-consumer_problem How can I implement this in Grails (maybe with a timer or even better by generating an event 'process queue')? Basically I'd like to a have a singleton service waiting for new events in the queue and processing them linearly (even if the queue is loaded by several concurrent processes). Any hints? Cheers!

  Read the article

• CSS3 gradient background set on body doesn't stretch but instead repeats?

  - by John Isaacks

  ok say the content inside the <body> totals 300px high. If I set the background of my <body> using -webkit-gradient or -moz-linear-gradient Then I maximize my window (or just make it taller than 300px) the gradient will be exactly 300px tall (the height of the content) and just repeat to fill the rest of the window. I am assuming this is not a bug since it is the same in both webkit and gecko. But is there a way to make the gradient stretch to fill the window instead of repeat?

  Read the article

• Help with hash tables and quadratic probing in Java

  - by user313458

  I really need help with inserting into a hash table. I'm just not totally getting it right now. Could someone explain quadratic and linear probing in layman's terms? public void insert(String key) { int homeLocation = 0; int location = 0; int count = 0; if (find(key).getLocation() == -1) // make sure key is not already in the table { //****** ADD YOUR CODE HERE FOR QUADRATIC PROBING ******** } } This is the code I'm working on. I'm not asking anyone to do it, I just really need help with learning the whole concept Any help would be greatly appreciated.

  Read the article

< Previous Page | 23 24 25 26 27 28 29 30 31 32 33 34  | Next Page >