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  • Speeding up Math calculations in Java

    - by Simon
    I have a neural network written in Java which uses a sigmoid transfer function defined as follows: private static double sigmoid(double x) { return 1 / (1 + Math.exp(-x)); } and this is called many times during training and computation using the network. Is there any way of speeding this up? It's not that it's slow, it's just that it is used a lot, so a small optimisation here would be a big overall gain.

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  • [Python] Tips for making a fraction calculator code more optimized (faster and using less memory)

    - by Logic Named Joe
    Hello Everyone, Basicly, what I need for the program to do is to act a as simple fraction calculator (for addition, subtraction, multiplication and division) for the a single line of input, for example: -input: 1/7 + 3/5 -output: 26/35 My initial code: import sys def euclid(numA, numB): while numB != 0: numRem = numA % numB numA = numB numB = numRem return numA for wejscie in sys.stdin: wyjscie = wejscie.split(' ') a, b = [int(x) for x in wyjscie[0].split("/")] c, d = [int(x) for x in wyjscie[2].split("/")] if wyjscie[1] == '+': licz = a * d + b * c mian= b * d nwd = euclid(licz, mian) konA = licz/nwd konB = mian/nwd wynik = str(konA) + '/' + str(konB) print(wynik) elif wyjscie[1] == '-': licz= a * d - b * c mian= b * d nwd = euclid(licz, mian) konA = licz/nwd konB = mian/nwd wynik = str(konA) + '/' + str(konB) print(wynik) elif wyjscie[1] == '*': licz= a * c mian= b * d nwd = euclid(licz, mian) konA = licz/nwd konB = mian/nwd wynik = str(konA) + '/' + str(konB) print(wynik) else: licz= a * d mian= b * c nwd = euclid(licz, mian) konA = licz/nwd konB = mian/nwd wynik = str(konA) + '/' + str(konB) print(wynik) Which I reduced to: import sys def euclid(numA, numB): while numB != 0: numRem = numA % numB numA = numB numB = numRem return numA for wejscie in sys.stdin: wyjscie = wejscie.split(' ') a, b = [int(x) for x in wyjscie[0].split("/")] c, d = [int(x) for x in wyjscie[2].split("/")] if wyjscie[1] == '+': print("/".join([str((a * d + b * c)/euclid(a * d + b * c, b * d)),str((b * d)/euclid(a * d + b * c, b * d))])) elif wyjscie[1] == '-': print("/".join([str((a * d - b * c)/euclid(a * d - b * c, b * d)),str((b * d)/euclid(a * d - b * c, b * d))])) elif wyjscie[1] == '*': print("/".join([str((a * c)/euclid(a * c, b * d)),str((b * d)/euclid(a * c, b * d))])) else: print("/".join([str((a * d)/euclid(a * d, b * c)),str((b * c)/euclid(a * d, b * c))])) Any advice on how to improve this futher is welcome. Edit: one more thing that I forgot to mention - the code can not make use of any libraries apart from sys.

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  • Storing information in the DOM?

    - by John
    Im making a small private message application in the form of a phone. Ten messages are shown at the time. And the list of messages are scrolled up/down by hiding them. Just how bad is it to use the DOM to store information in this way. My main goal for doing this is to reduce calls to the database. And instead of making a new call all the time, it only checks if any new messages has arrived and ads the new message(s). Whats the alternative, cookies anyone? Thank you for the time

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  • C++ Reserve Memory Space

    - by uray
    is there any way to reserve memory space to be used later by default Windows Memory Manager so that my application won't run out of memory if my program don't use space more than I have reserved at start of my program?

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  • Optimizing JS Array Search

    - by The.Anti.9
    I am working on a Browser-based media player which is written almost entirely in HTML 5 and JavaScript. The backend is written in PHP but it has one function which is to fill the playlist on the initial load. And the rest is all JS. There is a search bar that refines the playlist. I want it to refine as the person is typing, like most media players do. The only problem with this is that it is very slow and laggy as there are about 1000 songs in the whole program and there is likely to be more as time goes on. The original playlist load is an ajax call to a PHP page that returns the results as JSON. Each item has 4 attirbutes: artist album file url I then loop through each object and add it to an array called playlist. At the end of the looping a copy of playlist is created, backup. This is so that I can refine the playlist variable when people refine their search, but still repopulated it from backup without making another server request. The method refine() is called when the user types a key into the searchbox. It flushes playlist and searches through each property (not including url) of each object in the backup array for a match in the string. If there is a match in any of the properties, it appends the information to a table that displays the playlist, and adds it to the object to playlist for access by the actual player. Code for the refine() method: function refine() { $('#loadinggif').show(); $('#library').html("<table id='libtable'><tr><th>Artist</th><th>Album</th><th>File</th><th>&nbsp;</th></tr></table>"); playlist = []; for (var j = 0; j < backup.length; j++) { var sfile = new String(backup[j].file); var salbum = new String(backup[j].album); var sartist = new String(backup[j].artist); if (sfile.toLowerCase().search($('#search').val().toLowerCase()) !== -1 || salbum.toLowerCase().search($('#search').val().toLowerCase()) !== -1 || sartist.toLowerCase().search($('#search').val().toLowerCase()) !== -1) { playlist.push(backup[j]); num = playlist.length-1; $("<tr></tr>").html("<td>" + num + "</td><td>" + sartist + "</td><td>" + salbum + "</td><td>" + sfile + "</td><td><a href='#' onclick='setplay(" + num +");'>Play</a></td>").appendTo('#libtable'); } } $('#loadinggif').hide(); } As I said before, for the first couple of letters typed, this is very slow and laggy. I am looking for ways to refine this to make it much faster and more smooth.

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  • Results from two queries at once in sqlite?

    - by SF.
    I'm currently trying to optimize the sluggish process of retrieving a page of log entries from the SQLite database. I noticed I almost always retrieve next entries along with count of available entries: SELECT time, level, type, text FROM Logs WHERE level IN (%s) ORDER BY time DESC, id DESC LIMIT LOG_REQ_LINES OFFSET %d* LOG_REQ_LINES ; together with total count of records that can match current query: SELECT count(*) FROM Logs WHERE level IN (%s); (for a display "page n of m") I wonder, if I could concatenate the two queries, and ask them both in one sqlite3_exec() simply concatenating the query string. How should my callback function look then? Can I distinguish between the different types of data by argc? What other optimizations would you suggest?

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  • Optimizing C++ Tree Generation

    - by cam
    Hi, I'm generating a Tic-Tac-Toe game tree (9 seconds after the first move), and I'm told it should take only a few milliseconds. So I'm trying to optimize it, I ran it through CodeAnalyst and these are the top 5 calls being made (I used bitsets to represent the Tic-Tac-Toe board): std::_Iterator_base::_Orphan_me std::bitset<9::test std::_Iterator_base::_Adopt std::bitset<9::reference::operator bool std::_Iterator_base::~_Iterator_base void BuildTreeToDepth(Node &nNode, const int& nextPlayer, int depth) { if (depth > 0) { //Calculate gameboard states int evalBoard = nNode.m_board.CalculateBoardState(); bool isFinished = nNode.m_board.isFinished(); if (isFinished || (nNode.m_board.isWinner() > 0)) { nNode.m_winCount = evalBoard; } else { Ticboard tBoard = nNode.m_board; do { int validMove = tBoard.FirstValidMove(); if (validMove != -1) { Node f; Ticboard tempBoard = nNode.m_board; tempBoard.Move(validMove, nextPlayer); tBoard.Move(validMove, nextPlayer); f.m_board = tempBoard; f.m_winCount = 0; f.m_Move = validMove; int currPlay = (nextPlayer == 1 ? 2 : 1); BuildTreeToDepth(f,currPlay, depth - 1); nNode.m_winCount += f.m_board.CalculateBoardState(); nNode.m_branches.push_back(f); } else { break; } }while(true); } } } Where should I be looking to optimize it? How should I optimize these 5 calls (I don't recognize them=.

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  • How to optimize this script

    - by marks34
    I have written the following script. It opens a file, reads each line from it splitting by new line character and deleting first character in line. If line exists it's being added to array. Next each element of array is splitted by whitespace, sorted alphabetically and joined again. Every line is printed because script is fired from console and writes everything to file using standard output. I'd like to optimize this code to be more pythonic. Any ideas ? import sys def main(): filename = sys.argv[1] file = open(filename) arr = [] for line in file: line = line[1:].replace("\n", "") if line: arr.append(line) for line in arr: lines = line.split(" ") lines.sort(key=str.lower) line = ''.join(lines) print line if __name__ == '__main__': main()

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  • How to speed-up a simple method (preferably without changing interfaces or data structures)?

    - by baol
    I have some data structures: all_unordered_m is a big vector containing all the strings I need (all different) ordered_m is a small vector containing the indexes of a subset of the strings (all different) in the former vector position_m maps the indexes of objects from the first vector to their position in the second one. The string_after(index, reverse) method returns the string referenced by ordered_m after all_unordered_m[index]. ordered_m is considered circular, and is explored in natural or reverse order depending on the second parameter. The code is something like the following: struct ordered_subset { // [...] std::vector<std::string>& all_unordered_m; // size = n >> 1 std::vector<size_t> ordered_m; // size << n std::tr1::unordered_map<size_t, size_t> position_m; const std::string& string_after(size_t index, bool reverse) const { size_t pos = position_m.find(index)->second; if(reverse) pos = (pos == 0 ? orderd_m.size() - 1 : pos - 1); else pos = (pos == ordered.size() - 1 ? 0 : pos + 1); return all_unordered_m[ordered_m[pos]]; } }; Given that: I do need all of the data-structures for other purposes; I cannot change them because I need to access the strings: by their id in the all_unordered_m; by their index inside the various ordered_m; I need to know the position of a string (identified by it's position in the first vector) inside ordered_m vector; I cannot change the string_after interface without changing most of the program. How can I speed up the string_after method that is called billions of times and is eating up about 10% of the execution time?

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  • Need help optimizing this Django aggregate query

    - by Chris Lawlor
    I have the following model class Plugin(models.Model): name = models.CharField(max_length=50) # more fields which represents a plugin that can be downloaded from my site. To track downloads, I have class Download(models.Model): plugin = models.ForiegnKey(Plugin) timestamp = models.DateTimeField(auto_now=True) So to build a view showing plugins sorted by downloads, I have the following query: # pbd is plugins by download - commented here to prevent scrolling pbd = Plugin.objects.annotate(dl_total=Count('download')).order_by('-dl_total') Which works, but is very slow. With only 1,000 plugins, the avg. response is 3.6 - 3.9 seconds (devserver with local PostgreSQL db), where a similar view with a much simpler query (sorting by plugin release date) takes 160 ms or so. I'm looking for suggestions on how to optimize this query. I'd really prefer that the query return Plugin objects (as opposed to using values) since I'm sharing the same template for the other views (Plugins by rating, Plugins by release date, etc.), so the template is expecting Plugin objects - plus I'm not sure how I would get things like the absolute_url without a reference to the plugin object. Or, is my whole approach doomed to failure? Is there a better way to track downloads? I ultimately want to provide users some nice download statistics for the plugins they've uploaded - like downloads per day/week/month. Will I have to calculate and cache Downloads at some point? EDIT: In my test dataset, there are somewhere between 10-20 Download instances per Plugin - in production I expect this number would be much higher for many of the plugins.

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  • Help in optimizing a for loop in matlab

    - by HH
    I have a 1 by N double array consisting of 1 and 0. I would like to map all the 1 to symbol '-3' and '3' and all the 0 to symbol '-1' and '1' equally. Below is my code. As my array is approx 1 by 8 million, it is taking a very long time. How to speed things up? [row,ll] = size(Data); sym_zero = -1; sym_one = -3; for loop = 1 : row if Data(loop,1) == 0 Data2(loop,1) = sym_zero; if sym_zero == -1 sym_zero = 1; else sym_zero = -1; end else Data2(loop,1) = sym_one; if sym_one == -3 sym_zero = 3; else sym_zero = -3; end end end

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  • How to speed-up a simple method? (possibily without changing interfaces or data structures)

    - by baol
    Hello. I have some data structures: all_unordered_mordered_m is a big vector containing all the strings I need (all different) ordered_m is a small vector containing the indexes of a subset of the strings (all different) in the former vector position_m maps the indexes of objects from the first vector to their position in the second one. The string_after(index, reverse) method returns the string referenced by ordered_m after all_unordered_m[index]. ordered_m is considered circular, and is explored in natural or reverse order depending on the second parameter. The code is something like the following: struct ordered_subset { // [...] std::vector<std::string>& all_unordered_m; // size = n >> 1 std::vector<size_t> ordered_m; // size << n std::map<size_t, size_t> position_m; // positions of strings in ordered_m const std::string& string_after(size_t index, bool reverse) const { size_t pos = position_m.find(index)->second; if(reverse) pos = (pos == 0 ? orderd_m.size() - 1 : pos - 1); else pos = (pos == ordered.size() - 1 ? 0 : pos + 1); return all_unordered_m[ordered_m[pos]]; } }; Given that: I do need all of the data-structures for other purposes; I cannot change them because I need to access the strings: by their id in the all_unordered_m; by their index inside the various ordered_m; I need to know the position of a string (identified by it's position in the first vector) inside ordered_m vector; I cannot change the string_after interface without changing most of the program. How can I speed up the string_after method that is called billions of times and is eating up about 10% of the execution time?

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  • Why use one dimensional array instead of a two dimensional arrray?

    - by user3869145
    I was doing some work handling a lot of information and my partner told me that I was using too many matrices to manipulate the variables of the problem. The idea was to use one dimension arrays int a[] instead of the 2 dimensional arrays int b[][], to save memory and processing speed of the algorithm. How certain is that this change will accelerate the speed of execution or compilation of my code in c ++?

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  • SQL -- How is DISTINCT so fast without an index?

    - by Jonathan
    Hi, I have a database with a table called 'links' with 600 million rows in it in SQLite. There are 2 columns in the database - a "src" column and a "dest" column. At present there are no indices. There are a fair number of common values between src and dest, but also a fair number of duplicated rows. The first thing I'm trying to do is remove all the duplicate rows, and then perform some additional processing on the results, however I've been encountering some weird issues. Firstly, SELECT * FROM links WHERE src=434923 AND dest=5010182. Now this returns one result fairly quickly and then takes quite a long time to run as I assume it's performing a tablescan on the rest of the 600m rows. However, if I do SELECT DISTINCT * FROM links, then it immediately starts returning rows really quickly. The question is: how is this possible?? Surely for each row, the row must be compared against all of the other rows in the table, but this would require a tablescan of the remaining rows in the table which SHOULD takes ages! Any ideas why SELECT DISTINCT is so much quicker than a standard SELECT?

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  • Optimizing GDI+ drawing?

    - by user146780
    I'm using C++ and GDI+ I'm going to be making a vector drawing application and want to use GDI+ for the drawing. I'v created a simple test to get familiar with it: case WM_PAINT: GetCursorPos(&mouse); GetClientRect(hWnd,&rct); hdc = BeginPaint(hWnd, &ps); MemDC = CreateCompatibleDC(hdc); bmp = CreateCompatibleBitmap(hdc, 600, 600); SelectObject(MemDC,bmp); g = new Graphics(MemDC); for(int i = 0; i < 1; ++i) { SolidBrush sb(Color(255,255,255)); g->FillRectangle(&sb,rct.top,rct.left,rct.right,rct.bottom); } for(int i = 0; i < 250; ++i) { pts[0].X = 0; pts[0].Y = 0; pts[1].X = 10 + mouse.x * i; pts[1].Y = 0 + mouse.y * i; pts[2].X = 10 * i + mouse.x; pts[2].Y = 10 + mouse.y * i; pts[3].X = 0 + mouse.x; pts[3].Y = (rand() % 600) + mouse.y; Point p1, p2; p1.X = 0; p1.Y = 0; p2.X = 300; p2.Y = 300; g->FillPolygon(&b,pts,4); } BitBlt(hdc,0,0,900,900,MemDC,0,0,SRCCOPY); EndPaint(hWnd, &ps); DeleteObject(bmp); g->ReleaseHDC(MemDC); DeleteDC(MemDC); delete g; break; I'm wondering if I'm doing it right, or if I have areas killing the cpu. Because right now it takes ~ 1sec to render this and I want to be able to have it redraw itself very quickly. Thanks In a real situation would it be better just to figure out the portion of the screen to redraw and only redraw the elements withing bounds of this?

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  • Optimizing near-duplicate value search

    - by GApple
    I'm trying to find near duplicate values in a set of fields in order to allow an administrator to clean them up. There are two criteria that I am matching on One string is wholly contained within the other, and is at least 1/4 of its length The strings have an edit distance less than 5% of the total length of the two strings The Pseudo-PHP code: foreach($values as $value){ foreach($values as $match){ if( ( $value['length'] < $match['length'] && $value['length'] * 4 > $match['length'] && stripos($match['value'], $value['value']) !== false ) || ( $match['length'] < $value['length'] && $match['length'] * 4 > $value['length'] && stripos($value['value'], $match['value']) !== false ) || ( abs($value['length'] - $match['length']) * 20 < ($value['length'] + $match['length']) && 0 < ($match['changes'] = levenshtein($value['value'], $match['value'])) && $match['changes'] * 20 <= ($value['length'] + $match['length']) ) ){ $matches[] = &$match; } } } I've tried to reduce calls to the comparatively expensive stripos and levenshtein functions where possible, which has reduced the execution time quite a bit. However, as an O(n^2) operation this just doesn't scale to the larger sets of values and it seems that a significant amount of the processing time is spent simply iterating through the arrays. Some properties of a few sets of values being operated on Total | Strings | # of matches per string | | Strings | With Matches | Average | Median | Max | Time (s) | --------+--------------+---------+--------+------+----------+ 844 | 413 | 1.8 | 1 | 58 | 140 | 593 | 156 | 1.2 | 1 | 5 | 62 | 272 | 168 | 3.2 | 2 | 26 | 10 | 157 | 47 | 1.5 | 1 | 4 | 3.2 | 106 | 48 | 1.8 | 1 | 8 | 1.3 | 62 | 47 | 2.9 | 2 | 16 | 0.4 | Are there any other things I can do to reduce the time to check criteria, and more importantly are there any ways for me to reduce the number of criteria checks required (for example, by pre-processing the input values), since there is such low selectivity?

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  • Graph search problem with route restrictions

    - by Darcara
    I want to calculate the most profitable route and I think this is a type of traveling salesman problem. I have a set of nodes that I can visit and a function to calculate cost for traveling between nodes and points for reaching the nodes. The goal is to reach a fixed known score while minimizing the cost. This cost and rewards are not fixed and depend on the nodes visited before. The starting node is fixed. There are some restrictions on how nodes can be visited. Some simplified examples include: Node B can only be visited after A After node C has been visited, D or E can be visited. Visiting at least one is required, visiting both is permissible. Z can only be visited after at least 5 other nodes have been visited Once 50 nodes have been visited, the nodes A-M will no longer reward points Certain nodes can (and probably must) be visited multiple times Currently I can think of only two ways to solve this: a) Genetic Algorithms, with the fitness function calculating the cost/benefit of the generated route b) Dijkstra search through the graph, since the starting node is fixed, although the large number of nodes will probably make that not feasible memory wise. Are there any other ways to determine the best route through the graph? It doesn't need to be perfect, an approximated path is perfectly fine, as long as it's error acceptable. Would TSP-solvers be an option here?

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  • C#, Using Custom Generic Collection faster with objects than List

    - by Kaminari
    Hello, I'm using for now List< to iterate through some object collection and find matching element, The problem is that object has only 2 significant values Name and Link (strings) but has some other values wich I dont want to compare. I'm thinkig about using something like HashSet (wich is exactly what I'm searching for - fast) from .NET 3.5 but target framework has to be 2.0. There is something called Power Collections here: http://powercollections.codeplex.com/ But maybe there is other way? If not, can you suggest me a suitable custom collection?

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  • Does a c/c++ compiler optimize constant divisions by power-of-two value into shifts?

    - by porgarmingduod
    Question says it all. Does anyone know if the following... size_t div(size_t value) { const size_t x = 64; return value / x; } ...is optimized into? size_t div(size_t value) { return value >> 6; } Do compilers do this? (My interest lies in GCC). Are there situations where it does and others where it doesn't? I would really like to know, because every time I write a division that could be optimized like this I spend some mental energy wondering about whether precious nothings of a second is wasted doing a division where a shift would suffice.

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  • WPF Logical Tree - bottom up vs. top down

    - by Dor Rotman
    Hello, I've read the MSDN article about the layouts pass, that states: When a node is added or removed from the logical tree, property invalidations are raised on the node's parent and all its children. As a result, a top-down construction pattern should always be followed to avoid the cost of unnecessary invalidations on nodes that have already been validated. Now lets assume I do this. Won't the users see the control tree populate itself and the layout change several times during the control creation process? I want the whole control tree to just appear completely full. Thanks!

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