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  • How much detail should be in a project plan or spec?

    - by DeanMc
    I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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  • How to Implement Overlay blend method using opengles 1.1

    - by Cylon
    Blow is the algorithm of overlay. and i want using it on iphone, but iphone 3g only support opengles 1.1, can not using glsl. can i using blend function or texture combine to implement it. thank you /////////Reference from OpenGL Shading® Language Third Edition /////////// 19.6.12 Overlay OVERLAY first computes the luminance of the base value. If the luminance value is less than 0.5, the blend and base values are multiplied together. If the luminance value is greater than 0.5, a screen operation is performed. The effect is that the base value is mixed with the blend value, rather than being replaced. This allows patterns and colors to overlay the base image, but shadows and highlights in the base image are preserved. A discontinuity occurs where luminance = 0.5. To provide a smooth transition, we actually do a linear blend of the two equations for luminance in the range [0.45,0.55]. float luminance = dot(base, lumCoeff); if (luminance < 0.45) result = 2.0 * blend * base; else if (luminance 0.55) result = white - 2.0 * (white - blend) * (white - base); else { vec4 result1 = 2.0 * blend * base; vec4 result2 = white - 2.0 * (white - blend) * (white - base); result = mix(result1, result2, (luminance - 0.45) * 10.0); }

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  • Designing small comparable objects

    - by Thomas Ahle
    Intro Consider you have a list of key/value pairs: (0,a) (1,b) (2,c) You have a function, that inserts a new value between two current pairs, and you need to give it a key that keeps the order: (0,a) (0.5,z) (1,b) (2,c) Here the new key was chosen as the average between the average of keys of the bounding pairs. The problem is, that you list may have milions of inserts. If these inserts are all put close to each other, you may end up with keys such to 2^(-1000000), which are not easily storagable in any standard nor special number class. The problem How can you design a system for generating keys that: Gives the correct result (larger/smaller than) when compared to all the rest of the keys. Takes up only O(logn) memory (where n is the number of items in the list). My tries First I tried different number classes. Like fractions and even polynomium, but I could always find examples where the key size would grow linear with the number of inserts. Then I thought about saving pointers to a number of other keys, and saving the lower/greater than relationship, but that would always require at least O(sqrt) memory and time for comparison. Extra info: Ideally the algorithm shouldn't break when pairs are deleted from the list.

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  • CIE XYZ colorspace: do I have RGBA or XYZA?

    - by Tronic
    I plan to write a painting program based on linear combinations of xy plane points (0,1), (1,0) and (0,0). Such system works identically to RGB, except that the primaries are not within the gamut but at the corners of a triangle that encloses the entire gamut. I have seen the three points being referred to as X, Y and Z (upper case) somewhere, but I cannot find the page anymore (I marked them to the picture myself). My pixel format stores the intensity of each of those three components the same way as RGB does, together with alpha value. This allows using pretty much any image manipulation operation designed for RGBA without modifying the code. What is my format called? Is it XYZA, RGBA or something else? Google doesn't seem to know of XYZA. RGBA will get confused with sRGB + alpha (which I also need to use in the same program). Notice that the primaries X, Y and Z and their intensities have little to do with the x, y and z coordinates (lower case) that are more commonly used.

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  • Remove redundant SQL code

    - by Dave Jarvis
    Code The following code calculates the slope and intercept for a linear regression against a slathering of data. It then applies the equation y = mx + b against the same result set to calculate the value of the regression line for each row. Can the two separate sub-selects be joined so that the data and its slope/intercept are calculated without executing the data gathering part of the query twice? SELECT AVG(D.AMOUNT) as AMOUNT, Y.YEAR * ymxb.SLOPE + ymxb.INTERCEPT as REGRESSION_LINE, Y.YEAR as YEAR, MAKEDATE(Y.YEAR,1) as AMOUNT_DATE FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D, (SELECT ((avg(t.AMOUNT * t.YEAR)) - avg(t.AMOUNT) * avg(t.YEAR)) / (stddev( t.AMOUNT ) * stddev( t.YEAR )) as CORRELATION, ((sum(t.YEAR) * sum(t.AMOUNT)) - (count(1) * sum(t.YEAR * t.AMOUNT))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as SLOPE, ((sum( t.YEAR ) * sum( t.YEAR * t.AMOUNT )) - (sum( t.AMOUNT ) * sum(power(t.YEAR, 2)))) / (power(sum(t.YEAR), 2) - count(1) * sum(power(t.YEAR, 2))) as INTERCEPT FROM ( SELECT AVG(D.AMOUNT) as AMOUNT, Y.YEAR as YEAR, MAKEDATE(Y.YEAR,1) as AMOUNT_DATE FROM CITY C, STATION S, YEAR_REF Y, MONTH_REF M, DAILY D WHERE $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR ) t ) ymxb WHERE $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' GROUP BY Y.YEAR Question How do I execute the duplicate bits only once per query, instead of twice? The duplicate bit is the WHERE clause: $X{ IN, C.ID, CityCode } AND SQRT( POW( C.LATITUDE - S.LATITUDE, 2 ) + POW( C.LONGITUDE - S.LONGITUDE, 2 ) ) < $P{Radius} AND S.STATION_DISTRICT_ID = Y.STATION_DISTRICT_ID AND Y.YEAR BETWEEN 1900 AND 2009 AND M.YEAR_REF_ID = Y.ID AND M.CATEGORY_ID = $P{CategoryCode} AND M.ID = D.MONTH_REF_ID AND D.DAILY_FLAG_ID <> 'M' Related http://stackoverflow.com/questions/1595659/how-to-eliminate-duplicate-calculation-in-sql Thank you!

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  • Pseudo-quicksort time complexity

    - by Ord
    I know that quicksort has O(n log n) average time complexity. A pseudo-quicksort (which is only a quicksort when you look at it from far enough away, with a suitably high level of abstraction) that is often used to demonstrate the conciseness of functional languages is as follows (given in Haskell): quicksort :: Ord a => [a] -> [a] quicksort [] = [] quicksort (p:xs) = quicksort [y | y<-xs, y<p] ++ [p] ++ quicksort [y | y<-xs, y>=p] Okay, so I know this thing has problems. The biggest problem with this is that it does not sort in place, which is normally a big advantage of quicksort. Even if that didn't matter, it would still take longer than a typical quicksort because it has to do two passes of the list when it partitions it, and it does costly append operations to splice it back together afterwards. Further, the choice of the first element as the pivot is not the best choice. But even considering all of that, isn't the average time complexity of this quicksort the same as the standard quicksort? Namely, O(n log n)? Because the appends and the partition still have linear time complexity, even if they are inefficient.

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  • Good data structure for efficient insert/querying on arbitrary properties

    - by Juliet
    I'm working on a project where Arrays are the default data structure for everything, and every query is a linear search in the form of: Need a customer with a particular name? customer.Find(x => x.Name == name) Need a customer with a particular unique id? customer.Find(x => x.Id == id) Need a customer of a particular type and age? customer.Find(x => x is PreferredCustomer && x.Age >= age) Need a customer of a particular name and age? customer.Find(x => x.Name == name && x.Age == age) In almost all instances, the criteria for lookups is well-defined. For example, we only search for customers by one or more of the properties Id, Type, Name, or Age. We rarely search by anything else. Is a good data structure to support arbitrary queries of these types with lookup better than O(n)? Any out-of-the-box implementations for .NET?

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  • Intro Bar like stack overflow

    - by Dasa
    I have a simple top bar using jquery like the one on stackoverflow, but i want it to only appear on the first time a person visits the website. below is the HTML followed by the "bxSlider.js" file <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <head> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script> <script type="text/javascript" src="bxSlider.js"></script> <title>topbar</title> <style type="text/css" media="screen"> #message { font-family:Arial,Helvetica,sans-serif; position:fixed; top:0px; left:0px; width:100%; z-index:105; text-align:center; color:white; padding:2px 0px 2px 0px; background-color:#8E1609; } #example1 { text-align: center; width: 80%; } .close-notify { white-space: nowrap; float:right; margin-right:10px; color:#fff; text-decoration:none; padding-left:3px; padding-right:3px } .close-notify a { color: #fff; } h4, p { margin:0px; padding:0px; } </style> </head> <body> <DIV ID='message' style="display: none;"> <DIV ID="example1"> <DIV CLASS="item"> <h4>Head 1</h4> <p>Text 1</p> </div><!-- end item --> <DIV CLASS="item"> <h4>Head 2</h4> <p>Text 2</p> </div><!-- end item --> </div><!-- end example1 --> <a href="#" CLASS="close-notify" onclick="closeNotice()">X</a> </div> <script type="text/javascript"> $(document).ready(function() { $("#message").fadeIn("slow"); $('#example1').bxSlider({ mode: 'slide', speed: 250, wrapper_CLASS: 'example1_container' }); }); function closeNotice() { $("#message").fadeOut("slow"); } </script> </body> </html> /** * * * bxSlider: Content slider / fade / ticker using the jQuery javascript library. * * Author: Steven Wanderski * Email: [email protected] * URL: http://bxslider.com * * **/ jQuery.fn.bxSlider = function(options){ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Declare variables and functions ///////////////////////////////////////////////////////////////////////////////////////////////////////////// var defaults = { mode: 'slide', speed: 500, auto: false, auto_direction: 'left', pause: 2500, controls: true, prev_text: 'prev', next_text: 'next', width: $(this).children().width(), prev_img: '', next_img: '', ticker_direction: 'left', wrapper_class: 'container' }; options = $.extend(defaults, options); if(options.mode == 'ticker'){ options.auto = true; } var $this = $(this); var $parent_width = options.width; var current = 0; var is_working = false; var child_count = $this.children().size(); var i = 0; var j = 0; var k = 0; function animate_next(){ is_working = true; $this.animate({'left':'-' + $parent_width * 2 + 'px'}, options.speed, function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':first').appendTo($this); is_working = false; }); } function animate_prev(){ is_working = true; $this.animate({'left': 0}, options.speed, function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':last').insertBefore($this.children(':first')); is_working = false; }); } function fade(direction){ if(direction == 'next'){ var last_before_switch = child_count - 1; var start_over = 0; var incr = k + 1; }else if(direction == 'prev'){ var last_before_switch = 0; var start_over = child_count -1; var incr = k - 1; } is_working = true; if(k == last_before_switch){ $this.children().eq(k).fadeTo(options.speed, 0); $this.children().eq(start_over).fadeTo(options.speed, 1, function(){ is_working = false; k = start_over; }); }else{ $this.children().eq(k).fadeTo(options.speed, 0); $this.children().eq(incr).fadeTo(options.speed, 1, function(){ is_working = false; k = incr; }); } } function add_controls(){ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Check if user selected images to use for next / prev ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.prev_img != '' || options.next_img != ''){ $this.parent().append('<a class="slider_prev" href=""><img src="' + options.prev_img + '" alt=""/></a><a class="slider_next" href=""><img src="' + options.next_img + '" alt="" /></a>'); }else{ $this.parent().append('<a class="slider_prev" href="">' + options.prev_text + '</a><a class="slider_next" href="">' + options.next_text + '</a>'); } $this.parent().find('.slider_prev').css({'float':'left', 'outline':'0', 'color':'yellow'}); $this.parent().find('.slider_next').css({'float':'right', 'outline':'0', 'color':'yellow'}); ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Accomodate padding-top for controls when elements are absolutely positioned (only in fade mode) ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.mode == 'fade'){ $this.parent().find('.slider_prev').css({'paddingTop' : $this.children().height()}) $this.parent().find('.slider_next').css({'paddingTop' : $this.children().height()}) } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Actions when user clicks next / prev buttons ///////////////////////////////////////////////////////////////////////////////////////////////////////////// $this.parent().find('.slider_next').click(function(){ if(!is_working){ if(options.mode == 'slide'){ animate_next(); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){animate_next();}, options.pause); } }else if(options.mode == 'fade'){ fade('next'); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){fade('next');}, options.pause); } } } return false; }); $this.parent().find('.slider_prev').click(function(){ if(!is_working){ if(options.mode == 'slide'){ animate_prev(); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){animate_prev();}, options.pause); } }else if(options.mode == 'fade'){ fade('prev'); if(options.auto){ clearInterval($.t); $.t = setInterval(function(){fade('prev');}, options.pause); } } } return false; }); } function ticker() { if(options.ticker_direction == 'left'){ $this.animate({'left':'-' + $parent_width * 2 + 'px'}, options.speed, 'linear', function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':first').appendTo($this); ticker(); }); }else if(options.ticker_direction == 'right'){ $this.animate({'left': 0}, options.speed, 'linear', function(){ $this.css({'left':'-' + $parent_width + 'px'}).children(':last').insertBefore($this.children(':first')); ticker(); }); } } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Create content wrapper and set CSS ///////////////////////////////////////////////////////////////////////////////////////////////////////////// $this.wrap('<div class="' + options.wrapper_class + '"></div>'); //console.log($this.parent().css('paddingTop')); if(options.mode == 'slide' || options.mode == 'ticker'){ $this.parent().css({ 'overflow' : 'hidden', 'position' : 'relative', 'margin' : '0 auto', 'width' : options.width + 'px' }); $this.css({ 'width' : '999999px', 'position' : 'relative', 'left' : '-' + $parent_width + 'px' }); $this.children().css({ 'float' : 'left', 'width' : $parent_width }); $this.children(':last').insertBefore($this.children(':first')); }else if(options.mode == 'fade'){ $this.parent().css({ 'overflow' : 'hidden', 'position' : 'relative', 'width' : options.width + 'px' //'height' : $this.children().height() }); if(!options.controls){ $this.parent().css({'height' : $this.children().height()}); } $this.children().css({ 'position' : 'absolute', 'width' : $parent_width, 'listStyle' : 'none', 'opacity' : 0 }); $this.children(':first').css({ 'opacity' : 1 }); } ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Check if user selected "auto" ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(!options.auto){ add_controls(); }else{ if(options.mode == 'ticker'){ ticker(); }else{ ///////////////////////////////////////////////////////////////////////////////////////////////////////////// // Set a timed interval ///////////////////////////////////////////////////////////////////////////////////////////////////////////// if(options.mode == 'slide'){ if(options.auto_direction == 'left'){ $.t = setInterval(function(){animate_next();}, options.pause); }else if(options.auto_direction == 'right'){ $.t = setInterval(function(){animate_prev();}, options.pause); } }else if(options.mode == 'fade'){ if(options.auto_direction == 'left'){ $.t = setInterval(function(){fade('next');}, options.pause); }else if(options.auto_direction == 'right'){ $.t = setInterval(function(){fade('prev');}, options.pause); } } if(options.controls){ add_controls(); } } } }

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  • Android: Capturing the return of an activity.

    - by Chrispix
    I have a question regarding launching new activities. It boils down to this. I have 3 tabs on a view A) contains gMap activity B) camera activity C) some random text fields. Requirement is that the application runs in Portrait mode. All 3 tabs work as expected w/ the exception of the Camera Preview Surface (B). It is rotated 90 degrees. They only way to make it correct is to set the app to landscape which throws all my tabs around, and is pretty much unworkable. My solution is this : replace my camera activity with a regular activity that is empty w/ the exception of Intent i = new Intent(this,CameraActivity.class); startActivity(i); This launches my CameraActivity. And that works fine. I had to do a linear layout and include 3 images that look like real tabs, so I can try and mimic the operation of the tabs while rotating the screen to landscape and keep the visuals as portrait. The user can click one of the images(buttons) to display the next tab. This is my issue. It should exit my 'camera activity' returning to the 'blank activity' in a tab, where it should be interpreted to click the desiered tab from my image. The main thing is, when it returns, it returns to a blank (black) page under a tab (because it is 'empty'). How can I capture the return event back to the page that called the activity, and then see what action they performed? I can set an onclicklistener where I can respond to the fake tabs (images) being clicked to exit out of the camera activity. On exit, the tab should update so that is where you return. any Suggestions? Thanks,

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  • Update graph in real time from server

    - by user1869421
    I'm trying to update a graph with received data, so that the height of the bars increase as more data is received from the server via a websocket. But my code doesn't render a graph in the browser and plot the data points. I cannot see anything wrong with the code. I really need some help here please. ws = new WebSocket("ws://localhost:8888/dh"); var useData = [] //var chart; var chart = d3.select("body") .append("svg:svg") .attr("class", "chart") .attr("width", 420) .attr("height", 200); ws.onmessage = function(evt) { var distances = JSON.parse(evt.data); data = distances.miles; console.log(data); if(useData.length <= 10){ useData.push(data) } else { var draw = function(data){ // Set the width relative to max data value var x = d3.scale.linear() .domain([0, d3.max(useData)]) .range([0, 420]); var y = d3.scale.ordinal() .domain(useData) .rangeBands([0, 120]); var rect = chart.selectAll("rect") .data(useData) // enter rect rect.enter().append("svg:rect") .attr("y", y) .attr("width", x) .attr("height", y.rangeBand()); // update rect rect .attr("y", y) .attr("width", x) .attr("height", y.rangeBand()); var text = chart.selectAll("text") .data(useData) // enter text text.enter().append("svg:text") .attr("x", x) .attr("y", function (d) { return y(d) + y.rangeBand() / 2; }) .attr("dx", -3) // padding-right .attr("dy", ".35em") // vertical-align: middle .attr("text-anchor", "end") // text-align: right .text(String); // update text text .data(useData) .attr("x", x) .text(String); } useData.length = 0; } } Thanks

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  • Interpolating data points in Excel

    - by Niels Basjes
    Hi, I'm sure this is the kind of problem other have solved many times before. A group of people are going to do measurements (Home energy usage to be exact). All of them will do that at different times and in different intervals. So what I'll get from each person is a set of {date, value} pairs where there are dates missing in the set. What I need is a complete set of {date, value} pairs where for each date withing the range a value is known (either measured or calculated). I expect that a simple linear interpolation would suffice for this project. If I assume that it must be done in Excel. What is the best way to interpolate in such a dataset (so I have a value for every day) ? Thanks. NOTE: When these datasets are complete I'll determine the slope (i.e. usage per day) and from that we can start doing home-to-home comparisons. ADDITIONAL INFO After first few suggestions: I do not want to manually figure out where the holes are in my measurement set (too many incomplete measurement sets!!). I'm looking for something (existing) automatic to do that for me. So if my input is {2009-06-01, 10} {2009-06-03, 20} {2009-06-06, 110} Then I expect to automatically get {2009-06-01, 10} {2009-06-02, 15} {2009-06-03, 20} {2009-06-04, 50} {2009-06-05, 80} {2009-06-06, 110} Yes, I can write software that does this. I am just hoping that someone already has a "ready to run" software (Excel) feature for this (rather generic) problem.

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  • Parallel.For Batching

    - by chibacity
    Is there built-in support in the TPL for batching operations? I was recently playing with a routine to carry out character replacement on a character array which required a lookup table i.e. transliteration: for (int i = 0; i < chars.Length; i++) { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } } I could see that this could be trivially parallelized, so jumped in with a first stab which I knew would perform worse as the tasks were too fine-grained: Parallel.For(0, chars.Length, i => { char replaceChar; if (lookup.TryGetValue(chars[i], out replaceChar)) { chars[i] = replaceChar; } }); I then reworked the algorithm to use batching so that the work could be chunked onto different threads in less fine-grained batches. This made use of threads as expected and I got some near linear speed up. I'm sure that there must be built-in support for batching in the TPL. What is the syntax, and how do I use it? const int CharBatch = 100; int charLen = chars.Length; Parallel.For(0, ((charLen / CharBatch) + 1), i => { int batchUpper = ((i + 1) * CharBatch); for (int j = i * CharBatch; j < batchUpper && j < charLen; j++) { char replaceChar; if (lookup.TryGetValue(chars[j], out replaceChar)) { chars[j] = replaceChar; } } });

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  • What limits scaling in this simple OpenMP program?

    - by Douglas B. Staple
    I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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  • List of Big-O for PHP functions?

    - by Kendall Hopkins
    After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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  • Custom android preference type loses focus when typing

    - by Brian
    I created a simple preference class that shows an AutoCompleteTextView control and it displays properly but when i focus on the AutoCompleteTextView and start typing it brings up the keyboard but then immediately loses focus on the control. Any idea why this loses focus? Here's what i did to create the view. the inflated layout is just a basic linear layout with a title textview in it. I could change it to a dialog preference instead I guess but it'd be smoother if it could be part of the base view. @Override protected View onCreateView(ViewGroup parent) { LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); LinearLayout layout = (LinearLayout) inflater.inflate(R.layout.base_preference, null); if (mHint != null) { TextView hintView = (TextView) layout.findViewById(R.id.PreferenceHintTextView); hintView.setText(mHint); } TextView titleView = (TextView) layout.findViewById(R.id.PreferenceTitleTextView); titleView.setText(getTitle()); AutoCompleteTextView inputView = new AutoCompleteTextView(getContext()); inputView.setGravity(Gravity.FILL_HORIZONTAL); ArrayAdapter<CharSequence> adapter = new ArrayAdapter<CharSequence>(getContext(), R.layout.auto_complete_text_list_item, getEntries()); inputView.setAdapter(adapter); inputView.setThreshold(1); inputView.setOnItemSelectedListener(this); layout.addView(inputView); return layout; }

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  • C# Finding 2 positions 1-dimArray

    - by Chris
    Hello, In a method i am calculating the longest row of elements. The 1-dim array is filled up with random values (0 or 1). The method looks up the longest row (being 0 or 1, whatever is the longest). Meaning in for example: 1110100 --> the longest row would be 3 (3 * 1) 0110000 --> the longest row would be 4 (4 * 0) My problem is i am trying to perform some type of linear search to show the position of the row in the array. The first example has the longest row of 3 elements (3 times 1). For 1110100 the position in the array would be 0 - 2 (index) For 0110000 the position in the array would be 3 - 6 (index) I have been trying with foreaches, for loops etc..but i cannot seem to get the proper indexes of both. Cannot seem to display both positions properly. For the first example the correct output wouldbe: The largest row of same elements of the array consists of 3 elements on the position 0 - 2. The longest row of elements gets of same elements get calculated as the following: public int BerekenDeelrij (int [] table) ( int count = 0; final int value = 0; int largest = 0; foreach (int value in table) ( if (value == last value) counter + +; else ( largest = Math.Max largest (largest, counter); final value = value count = 1; ) ) Math.Max return (largest, counter); ) Best Regards.

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  • Pre Project Documentation

    - by DeanMc
    I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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  • Out-of-memory algorithms for addressing large arrays

    - by reve_etrange
    I am trying to deal with a very large dataset. I have k = ~4200 matrices (varying sizes) which must be compared combinatorially, skipping non-unique and self comparisons. Each of k(k-1)/2 comparisons produces a matrix, which must be indexed against its parents (i.e. can find out where it came from). The convenient way to do this is to (triangularly) fill a k-by-k cell array with the result of each comparison. These are ~100 X ~100 matrices, on average. Using single precision floats, it works out to 400 GB overall. I need to 1) generate the cell array or pieces of it without trying to place the whole thing in memory and 2) access its elements (and their elements) in like fashion. My attempts have been inefficient due to reliance on MATLAB's eval() as well as save and clear occurring in loops. for i=1:k [~,m] = size(data{i}); cur_var = ['H' int2str(i)]; %# if i == 1; save('FileName'); end; %# If using a single MAT file and need to create it. eval([cur_var ' = cell(1,k-i);']); for j=i+1:k [~,n] = size(data{j}); eval([cur_var '{i,j} = zeros(m,n,''single'');']); eval([cur_var '{i,j} = compare(data{i},data{j});']); end save(cur_var,cur_var); %# Add '-append' when using a single MAT file. clear(cur_var); end The other thing I have done is to perform the split when mod((i+j-1)/2,max(factor(k(k-1)/2))) == 0. This divides the result into the largest number of same-size pieces, which seems logical. The indexing is a little more complicated, but not too bad because a linear index could be used. Does anyone know/see a better way?

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  • Why are changes to classes ignored after dom changes?

    - by Lg102
    I have a price grid that uses relative positioning to move a field around, beneath a box with: overflow: hidden;. In this is field, there are absolute-positioned boxes containing prices. When this box is hovered, the matching values above and left of the will change color. In order to achieve this, a class is toggled using jQuery. This initially works. However, after the grid is moved, the class change doesn't affect the block above the grid anymore. In the Chrome console, i can see the class being added, but it's css-styling isn't applied. No other styles for the element have changed. I am 100% sure there is no other style-rule influencing the element, it just stops responding to the change in class after the DOM has been altered. Can i 'refresh' the DOM somehow? Edit: I've tried to get the relevant code only: Adding the cell in the first place: $("#price_dates_cells").append("<div id='"+weekday[theBeginDate.getDay()]+"-"+theBeginDate.getDate()+"-"+(theBeginDate.getMonth()-1)+"' class='datecell' style='left: "+( Math.floor( difference / ( 3600 * 24 * 1000) ) * ( cellwidth ) )+"px'>"+weekday[theBeginDate.getDay()]+"<br>"+theBeginDate.getDate()+" "+yearmonth[theBeginDate.getMonth()]+"</div>"); Toggle the class: var str_element = "#"+weekday[Bdate.getDay()]+"-"+Bdate.getDate()+"-"+(Bdate.getMonth()-1); $(str_element).toggleClass("red"); and the movement that seems to cause the problem: $('#price_grid').animate({"top": (( ( horizontalMovement ) * cellheight)) }, 'fast', 'linear');

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  • Efficient (basic) regular expression implementation for streaming data

    - by Brendan Dolan-Gavitt
    I'm looking for an implementation of regular expression matching that operates on a stream of data -- i.e., it has an API that allows a user to pass in one character at a time and report when a match is found on the stream of characters seen so far. Only very basic (classic) regular expressions are needed, so a DFA/NFA based implementation seems like it would be well-suited to the problem. Based on the fact that it's possible to do regular expression matching using a DFA/NFA in a single linear sweep, it seems like a streaming implementation should be possible. Requirements: The library should try to wait until the full string has been read before performing the match. The data I have really is streaming; there is no way to know how much data will arrive, it's not possible to seek forward or backward. Implementing specific stream matching for a couple special cases is not an option, as I don't know in advance what patterns a user might want to look for. For the curious, my use case is the following: I have a system which intercepts memory writes inside a full system emulator, and I would like to have a way to identify memory writes that match a regular expression (e.g., one could use this to find the point in the system where a URL is written to memory). I have found (links de-linkified because I don't have enough reputation): stackoverflow.com/questions/1962220/apply-a-regex-on-stream stackoverflow.com/questions/716927/applying-a-regular-expression-to-a-java-i-o-stream www.codeguru.com/csharp/csharp/cs_data/searching/article.php/c14689/Building-a-Regular-Expression-Stream-Search-with-the-NET-Framework.htm But all of these attempt to convert the stream to a string first and then use a stock regular expression library. Another thought I had was to modify the RE2 library, but according to the author it is architected around the assumption that the entire string is in memory at the same time. If nothing's available, then I can start down the unhappy path of reinventing this wheel to fit my own needs, but I'd really rather not if I can avoid it. Any help would be greatly appreciated!

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  • breadth-first traversal of directory tree is not lazy

    - by user855443
    I try to traverse the diretory tree. A naive depth-first traversal seems not to produce the data in a lazy fashion and runs out of memory. I next tried a breadth first approach, which shows the same problem - it uses all the memory available and then crashes. the code i have is: getFilePathBreadtFirst :: FilePath -> IO [FilePath] getFilePathBreadtFirst fp = do fileinfo <- getInfo fp res :: [FilePath] <- if isReadableDirectory fileinfo then do children <- getChildren fp lower <- mapM getFilePathBreadtFirst children return (children ++ concat lower) return (children ++ concat () else return [fp] -- should only return the files? return res getChildren :: FilePath -> IO [FilePath] getChildren path = do names <- getUsefulContents path let namesfull = map (path </>) names return namesfull testBF fn = do -- crashes for /home/frank, does not go to swap fps <- getFilePathBreadtFirst fn putStrLn $ unlines fps I think all the code is either linear or tail recursive, and I would expect that the listing of filenames starts immediately, but in fact it does not. Where is the error in my code and my thinking? where have I lost lazy evaluation?

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  • R Tree 50,000 foot overview?

    - by roufamatic
    I'm working on a school project that involves taking a lat/long point and finding the top five closest points in a known list of places. The list is to be stored in memory, with the caveat that we must choose an "appropriate data structure" -- that is, we cannot simply store all the places in an array and compare distances one-by-one in a linear fashion. The teacher suggested grouping the place data by US State to prevent calculating the distance for places that are obviously too far away. I think I can do better. From my research online it seems like an R-Tree or one of its variants might be a neat solution. Unfortunately, that sentence is as far as I've gotten with understanding the actual technique, as the literature is simply too dense for my non-academic head. Can somebody give me a really high overview of what the process is for populating an R-Tree with lat/long data, and then traversing the tree to find those 5 nearest neighbors of a given point? Additionally the project is in C, and I don't have to reinvent the wheel on this, so if you've used an existing open source C implementation of an R Tree I'd be interested in your experiences.

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  • Convert SVG to PDF

    - by Adrian Smith
    How would one go about converting a SVG file to a PDF programatically? (I need to alter the SVG in certain respects before generating the PDF so simply pre-converting it using a tool won't be sufficient.) Ideally using Java but Perl or PHP would be fine too. Obviously I am basically considering Apache FOP and Batik with Java. However no matter how long I search I cannot find a simple introduction on how to do it. Things like SVGConverter have descriptions like "Defines the interface for classes that are able to convert part or all of a GraphicContext", but I don't really know what that means. I have this feeling there must be an API to do this quite simply, provided by FOP or Batik, but I'm just not able to find it at the moment (or perhaps it really doesn't exist.) In terms of the supported SVG features I need, the file has some paths which are filled with some linear gradients. Ideally if I could pass the SVG in as a DOM Document that would be ideal; then I would load my template SVG file, change it as specified by the user, and then generate the PDF.

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  • 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?

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  • Algorithm to determine if array contains n...n+m?

    - by Kyle Cronin
    I saw this question on Reddit, and there were no positive solutions presented, and I thought it would be a perfect question to ask here. This was in a thread about interview questions: Write a method that takes an int array of size m, and returns (True/False) if the array consists of the numbers n...n+m-1, all numbers in that range and only numbers in that range. The array is not guaranteed to be sorted. (For instance, {2,3,4} would return true. {1,3,1} would return false, {1,2,4} would return false. The problem I had with this one is that my interviewer kept asking me to optimize (faster O(n), less memory, etc), to the point where he claimed you could do it in one pass of the array using a constant amount of memory. Never figured that one out. Along with your solutions please indicate if they assume that the array contains unique items. Also indicate if your solution assumes the sequence starts at 1. (I've modified the question slightly to allow cases where it goes 2, 3, 4...) edit: I am now of the opinion that there does not exist a linear in time and constant in space algorithm that handles duplicates. Can anyone verify this? The duplicate problem boils down to testing to see if the array contains duplicates in O(n) time, O(1) space. If this can be done you can simply test first and if there are no duplicates run the algorithms posted. So can you test for dupes in O(n) time O(1) space?

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