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  • Optimizing Code

    - by Claudiu
    You are given a heap of code in your favorite language which combines to form a rather complicated application. It runs rather slowly, and your boss has asked you to optimize it. What are the steps you follow to most efficiently optimize the code? What strategies have you found to be unsuccessful when optimizing code? Re-writes: At what point do you decide to stop optimizing and say "This is as fast as it'll get without a complete re-write." In what cases would you advocate a simple complete re-write anyway? How would you go about designing it?

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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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  • Optimize SQL query (Facebook-like application)

    - by fabriciols
    My application is similar to Facebook, and I'm trying to optimize the query that get user records. The user records are that he as src ou dst. The src is in usermuralentry directly, the dst list are in usermuralentry_user. So, a entry can have one src and many dst. I have those tables: mysql> desc usermuralentry ; +-----------------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------+------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | user_src_id | int(11) | NO | MUL | NULL | | | private | tinyint(1) | NO | | NULL | | | content | longtext | NO | | NULL | | | date | datetime | NO | | NULL | | | last_update | datetime | NO | | NULL | | +-----------------+------------------+------+-----+---------+----------------+ 10 rows in set (0.10 sec) mysql> desc usermuralentry_user ; +-------------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | usermuralentry_id | int(11) | NO | MUL | NULL | | | userinfo_id | int(11) | NO | MUL | NULL | | +-------------------+---------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) And the following query to retrieve information from two users. mysql> explain SELECT * FROM usermuralentry AS a , usermuralentry_user AS b WHERE a.user_src_id IN ( 1, 2 ) OR ( a.id = b.usermuralentry_id AND b.userinfo_id IN ( 1, 2 ) ); +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | 1 | SIMPLE | b | ALL | usermuralentry_id,usermuralentry_user_bcd7114e,usermuralentry_user_6b192ca7 | NULL | NULL | NULL | 147188 | | | 1 | SIMPLE | a | ALL | PRIMARY | NULL | NULL | NULL | 1371289 | Range checked for each record (index map: 0x1) | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ 2 rows in set (0.00 sec) but it is taking A LOT of time... Some tips to optimize? Can the table schema be better in my application?

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  • Find all A^x in a given range

    - by Austin Henley
    I need to find all monomials in the form AX that when evaluated falls within a range from m to n. It is safe to say that the base A is greater than 1, the power X is greater than 2, and only integers need to be used. For example, in the range 50 to 100, the solutions would be: 2^6 3^4 4^3 My first attempt to solve this was to brute force all combinations of A and X that make "sense." However this becomes too slow when used for very large numbers in a big range since these solutions are used in part of much more intensive processing. Here is the code: def monoSearch(min, max): base = 2 power = 3 while 1: while base**power < max: if base**power > min: print "Found " + repr(base) + "^" + repr(power) + " = " + repr(base**power) power = power + 1 base = base + 1 power = 3 if base**power > max: break I could remove one base**power by saving the value in a temporary variable but I don't think that would make a drastic effect. I also wondered if using logarithms would be better or if there was a closed form expression for this. I am open to any optimizations or alternatives to finding the solutions.

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  • How to properly cast a global memory array using the uint4 vector in CUDA to increase memory throughput?

    - by charis
    There are generally two techniques to increase the memory throughput of the global memory on a CUDA kernel; memory accesses coalescence and accessing words of at least 4 bytes. With the first technique accesses to the same memory segment by threads of the same half-warp are coalesced to fewer transactions while be accessing words of at least 4 bytes this memory segment is effectively increased from 32 bytes to 128. To access 16-byte instead of 1-byte words when there are unsigned chars stored in the global memory, the uint4 vector is commonly used by casting the memory array to uint4: uint4 *text4 = ( uint4 * ) d_text; var = text4[i]; In order to extract the 16 chars from var, i am currently using bitwise operations. For example: s_array[j * 16 + 0] = var.x & 0x000000FF; s_array[j * 16 + 1] = (var.x >> 8) & 0x000000FF; s_array[j * 16 + 2] = (var.x >> 16) & 0x000000FF; s_array[j * 16 + 3] = (var.x >> 24) & 0x000000FF; My question is, is it possible to recast var (or for that matter *text4) to unsigned char in order to avoid the additional overhead of the bitwise operations?

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  • How to make this JavaScript much faster?

    - by Ralph
    Still trying to answer this question, and I think I finally found a solution, but it runs too slow. var $div = $('<div>') .css({ 'border': '1px solid red', 'position': 'absolute', 'z-index': '65535' }) .appendTo('body'); $('body *').live('mousemove', function(e) { var topElement = null; $('body *').each(function() { if(this == $div[0]) return true; var $elem = $(this); var pos = $elem.offset(); var width = $elem.width(); var height = $elem.height(); if(e.pageX > pos.left && e.pageY > pos.top && e.pageX < (pos.left + width) && e.pageY < (pos.top + height)) { var zIndex = document.defaultView.getComputedStyle(this, null).getPropertyValue('z-index'); if(zIndex == 'auto') zIndex = $elem.parents().length; if(topElement == null || zIndex > topElement.zIndex) { topElement = { 'node': $elem, 'zIndex': zIndex }; } } }); if(topElement != null ) { var $elem = topElement.node; $div.offset($elem.offset()).width($elem.width()).height($elem.height()); } }); It basically loops through all the elements on the page and finds the top-most element beneath the cursor. Is there maybe some way I could use a quad-tree or something and segment the page so the loop runs faster?

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  • Optimizing PHP code (trying to determine min/max/between case)

    - by Swizzh
    I know this code-bit does not conform very much to best coding practices, and was looking to improve it, any ideas? if ($query['date_min'] != _get_date_today()) $mode_min = true; if ($query['date_max'] != _get_date_today()) $mode_max = true; if ($mode_max && $mode_min) $mode = "between"; elseif ($mode_max && !$mode_min) $mode = "max"; elseif (!$mode_max && $mode_min) $mode = "min"; else return; if ($mode == "min" || $mode == "between") { $command_min = "A"; } if ($mode == "max" || $mode == "between") { $command_max = "B"; } if ($mode == "between") { $command = $command_min . " AND " . $command_max; } else { if ($mode == "min") $command = $command_min; if ($mode == "max") $command = $command_max; } echo $command;

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  • How to optimize my game calendar in C#?

    - by MartyIX
    Hi, I've implemented a simple calendar (message system) for my game which consists from: 1) List<Event> calendar; 2) public class Event { /// <summary> /// When to process the event /// </summary> public Int64 when; /// <summary> /// Which object should process the event /// </summary> public GameObject who; /// <summary> /// Type of event /// </summary> public EventType what; public int posX; public int posY; public int EventID; } 3) calendar.Add(new Event(...)) The problem with this code is that even thought the number of messages is not excessise per second. It allocates still new memory and GC will once need to take care of that. The garbage collection may lead to a slight lag in my game and therefore I'd like to optimalize my code. My considerations: To change Event class in a structure - but the structure is not entirely small and it takes some time to copy it wherever I need it. Reuse Event object somehow (add queue with used events and when new event is needed I'll just take from this queue). Does anybody has other idea how to solve the problem? Thanks for suggestions!

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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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  • Optimising ruby regexp -- lots of match groups

    - by Farcaller
    I'm working on a ruby baser lexer. To improve performance, I joined up all tokens' regexps into one big regexp with match group names. The resulting regexp looks like: /\A(?<__anonymous_-1038694222803470993>(?-mix:\n+))|\A(?<__anonymous_-1394418499721420065>(?-mix:\/\/[\A\n]*))|\A(?<__anonymous_3077187815313752157>(?-mix:include\s+"[\A"]+"))|\A(?<LET>(?-mix:let\s))|\A(?<IN>(?-mix:in\s))|\A(?<CLASS>(?-mix:class\s))|\A(?<DEF>(?-mix:def\s))|\A(?<DEFM>(?-mix:defm\s))|\A(?<MULTICLASS>(?-mix:multiclass\s))|\A(?<FUNCNAME>(?-mix:![a-zA-Z_][a-zA-Z0-9_]*))|\A(?<ID>(?-mix:[a-zA-Z_][a-zA-Z0-9_]*))|\A(?<STRING>(?-mix:"[\A"]*"))|\A(?<NUMBER>(?-mix:[0-9]+))/ I'm matching it to my string producing a MatchData where exactly one token is parsed: bigregex =~ "\n ... garbage" puts $~.inspect Which outputs #<MatchData "\n" __anonymous_-1038694222803470993:"\n" __anonymous_-1394418499721420065:nil __anonymous_3077187815313752157:nil LET:nil IN:nil CLASS:nil DEF:nil DEFM:nil MULTICLASS:nil FUNCNAME:nil ID:nil STRING:nil NUMBER:nil> So, the regex actually matched the "\n" part. Now, I need to figure the match group where it belongs (it's clearly visible from #inspect output that it's _anonymous-1038694222803470993, but I need to get it programmatically). I could not find any option other than iterating over #names: m.names.each do |n| if m[n] type = n.to_sym resolved_type = (n.start_with?('__anonymous_') ? nil : type) val = m[n] break end end which verifies that the match group did have a match. The problem here is that it's slow (I spend about 10% of time in the loop; also 8% grabbing the @input[@pos..-1] to make sure that \A works as expected to match start of string (I do not discard input, just shift the @pos in it). You can check the full code at GH repo. Any ideas on how to make it at least a bit faster? Is there any option to figure the "successful" match group easier?

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  • Optimize INSERT / UPDATE / DELETE operation

    - by clime
    I wonder if the following script can be optimized somehow. It does write a lot to disk because it deletes possibly up-to-date rows and reinserts them. I was thinking about applying something like "insert ... on duplicate key update" and found some possibilities for single-row updates but I don't know how to apply it in the context of INSERT INTO ... SELECT query. CREATE OR REPLACE FUNCTION update_member_search_index() RETURNS VOID AS $$ DECLARE member_content_type_id INTEGER; BEGIN member_content_type_id := (SELECT id FROM django_content_type WHERE app_label='web' AND model='member'); DELETE FROM watson_searchentry WHERE content_type_id = member_content_type_id; INSERT INTO watson_searchentry (engine_slug, content_type_id, object_id, object_id_int, title, description, content, url, meta_encoded) SELECT 'default', member_content_type_id, web_member.id, web_member.id, web_member.name, '', web_user.email||' '||web_member.normalized_name||' '||web_country.name, '', '{}' FROM web_member INNER JOIN web_user ON (web_member.user_id = web_user.id) INNER JOIN web_country ON (web_member.country_id = web_country.id) WHERE web_user.is_active=TRUE; END; $$ LANGUAGE plpgsql; EDIT: Schemas of web_member, watson_searchentry, web_user, web_country: http://pastebin.com/3tRVPPVi. (content_type_id, object_id_int) in watson_searchentry is unique pair in the table but atm the index is not present (there is no use for it). This script should be run at most once a day for full rebuilds of search index.

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  • [C++] Is it possible to roll a significantly faster version of sqrt

    - by John
    In an app I'm profiling, I found that in some scenarios this functions are able to take over 10% of total execution time. I've seen discussion over the years of faster sqrt implementations using sneaky floating-point trickery, but I don't know if such things are outdated on modern CPUs. MSVC++ 2008 compiler is being used, for reference... though I'd assume sqrt is not going to add much overhead though.

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  • Is there a way to optimise finding text items on a page (not regex)

    - by Jeepstone
    After seeing several threads rubbishing the regexp method of finding a term to match within an HTML document, I've used the Simple HTML DOM PHP parser (http://simplehtmldom.sourceforge.net/) to get the bits of text I'm after, but I want to know if my code is optimal. It feels like I'm looping too many times. Is there a way to optimise the following loop? //Get the HTML and look at the text nodes $html = str_get_html($buffer); //First we match the <body> tag as we don't want to change the <head> items foreach($html->find('body') as $body) { //Then we get the text nodes, rather than any HTML foreach($body->find('text') as $text) { //Then we match each term foreach ($terms as $term) { //Match to the terms within the text nodes $text->outertext = str_replace($term, '<span class="highlight">'.$term.'</span>', $text->outertext); } } } For example, would it make a difference to determine check if I have any matches before I start the loop maybe?

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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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  • serving cached files based upon cookie?

    - by matthewsteiner
    So I realized something today. In my application, you really can't get anywhere (except the front page) unless you're logged in. And you can't be logged in without a cookie. So my front page could be cached, except the problem is if you are logged in (have a cookie set) then it should just redirect into the application. Is there a way for nginx to look for a cookie and if it finds it then deliver a cached file? Just an idea...

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  • super-space-optimized code

    - by Will
    There are key self-contained algorithms - particularly cryptography-related such as AES, RSA, SHA1 etc - which you can find many implementations of for free on the internet. Some are written to be nice and portable clean C. Some are written to be fast - often with macros, and explicit unrolling. As far as I can tell, none are trying to be especially super-small - so I'm resigned to writing my own - explicitly AES128 decryption and SHA1 for ARM THUMB2. What patterns and tricks can I use to do so? Are there compilers/tools that can roll-up code?

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  • optimizing oracle query

    - by deming
    I'm having a hard time wrapping my head around this query. it is taking almost 200+ seconds to execute. I've pasted the execution plan as well. SELECT user_id , ROLE_ID , effective_from_date , effective_to_date , participant_code , ACTIVE FROM CMP_USER_ROLE E WHERE ACTIVE = 0 AND (SYSDATE BETWEEN effective_from_date AND effective_to_date OR TO_CHAR(effective_to_date,'YYYY-Q') = '2010-2') AND participant_code = 'NY005' AND NOT EXISTS ( SELECT 1 FROM CMP_USER_ROLE r WHERE r.USER_ID= E.USER_ID AND r.role_id = E.role_id AND r.ACTIVE = 4 AND E.effective_to_date <= (SELECT MAX(last_update_date) FROM CMP_USER_ROLE S WHERE S.role_id = r.role_id AND S.role_id = r.role_id AND S.ACTIVE = 4 )) Explain plan ----------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 37 | 154 (2)| 00:00:02 | |* 1 | FILTER | | | | | | |* 2 | TABLE ACCESS BY INDEX ROWID | USER_ROLE | 1 | 37 | 30 (0)| 00:00:01 | |* 3 | INDEX RANGE SCAN | N_USER_ROLE_IDX6 | 27 | | 3 (0)| 00:00:01 | |* 4 | FILTER | | | | | | | 5 | HASH GROUP BY | | 1 | 47 | 124 (2)| 00:00:02 | |* 6 | TABLE ACCESS BY INDEX ROWID | USER_ROLE | 159 | 3339 | 119 (1)| 00:00:02 | | 7 | NESTED LOOPS | | 11 | 517 | 123 (1)| 00:00:02 | |* 8 | TABLE ACCESS BY INDEX ROWID| USER_ROLE | 1 | 26 | 4 (0)| 00:00:01 | |* 9 | INDEX RANGE SCAN | N_USER_ROLE_IDX5 | 1 | | 3 (0)| 00:00:01 | |* 10 | INDEX RANGE SCAN | N_USER_ROLE_IDX2 | 957 | | 74 (2)| 00:00:01 | -----------------------------------------------------------------------------------------------------

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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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  • Getting confused why i dont get expected amount ?

    - by Stackfan
    I have 1 result and which i will receive in Bank account, Based on that account i have to Put a balance to user account. How can you find the Handling cost from total tried 491.50 / 0.95 = 517.36 which is wrong ? It should be 500.00 (to my expectation) User balance requires 500.00 When 500.00 selected he gets 5% discount There is a handling cost for this ex: 1) Discount: 500.00 - 5% = 475.00 2) Handling cost: (475.00 x 0.034) + 0.35 = 16.50 3) Total: 475.00 + 16.50 = 491.50 So problem is from 491.50, i have to find atleast handling cost to get promised Balance. Any solution ? Cant figure it out myself...

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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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  • Optimize jQuery code

    - by Dannemannen
    Greetings, Just built some stuff with jQuery, everything works perfect(!), but I would like it to be as optimzed as possible.. what small changes can I do to my code? $(document).ready(function() { // hide the indicator, we use it later $(".indicator").hide(); // start the animation of the progressbar $(".fill").animate({ width: "50px",}, 4000, function() { $(".indicator").effect("pulsate", { times:999 }, 2000);}); // notify-me ajax function $(".btn-submit").click(function() { // get the variable email and put it in a new variable var email = $("input#mail").val(); var dataString = 'mail='+email; $.ajax({ type: "POST", url: "/mail.php", data: dataString, dataType: "json", success: function(msg){ // JSON return, lets do some magic if(msg.status == "ok") { $("#response-box").fadeIn("slow").delay(2000).fadeOut("slow"); $("#fade").fadeIn("slow").delay(2000).fadeOut("slow"); $("#response-box .inner").html("<h1>Thank you.</h1>We'll keep in touch!"); $("#mail").val("e.g. [email protected]"); } else { $("#response-box").fadeIn("slow").delay(2000).fadeOut("slow"); $("#fade").fadeIn("slow").delay(2000).fadeOut("slow"); $("#response-box .inner").html("<h1>Oops.</h1>Please try again!"); } } }); //make sure the form doesn't post return false; }); });

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