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• getting number of hours until the next event

  - by Andrew Heath

  I've got a table with this data: [ID] [event_name] [last_event] 1 stats 2011-01-01 01:47:32 last_event is a timestamp. The event occurs every 48 hours (it's a cron job). I'd like to show my users the number of hours until the event executes again. So far I've got: SELECT (lastFinish + INTERVAL 48 HOUR) FROM `cron_status` which gives me the exact time and date of the next occurence: 2011-01-03 01:47:32. So I figured if I subtracted the current datetime... SELECT ((lastFinish + INTERVAL 48 HOUR) - SYSDATE()) FROM `cron_status` which (I think?) gives me the difference in unix time: 1980015. But if I divide that by 3600 to convert the seconds to hours... SELECT (((lastFinish + INTERVAL 48 HOUR) - SYSDATE())/3600) FROM `cron_status` I get numbers an order of magnitude too high: 549.99. Where am I going wrong? The target is returning the number of hours until the next execution. Thank you!

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• Questions about the Backpropogation Algorithm

  - by Colemangrill

  I have a few questions concerning backpropogation. I'm trying to learn the fundamentals behind neural network theory and wanted to start small, building a simple XOR classifier. I've read a lot of articles and skimmed multiple textbooks - but I can't seem to teach this thing the pattern for XOR. Firstly, I am unclear about the learning model for backpropogation. Here is some pseudo-code to represent how I am trying to train the network. [Lets assume my network is setup properly (ie: multiple inputs connect to a hidden layer connect to an output layer and all wired up properly)]. SET guess = getNetworkOutput() // Note this is using a sigmoid activation function. SET error = desiredOutput - guess SET delta = learningConstant * error * sigmoidDerivative(guess) For Each Node in inputNodes For Each Weight in inputNodes[n] inputNodes[n].weight[j] += delta; // At this point, I am assuming the first layer has been trained. // Then I recurse a similar function over the hidden layer and output layer. // The prime difference being that it further divi's up the adjustment delta. I realize this is probably not enough to go off of, and I will gladly expound on any part of my implementation. Using the above algorithm, my neural network does get trained, kind of. But not properly. The output is always XOR 1 1 [smallest number] XOR 0 0 [largest number] XOR 1 0 [medium number] XOR 0 1 [medium number] I can never train the [1,1] [0,0] to be the same value. If you have any suggestions, additional resources, articles, blogs, etc for me to look at I am very interested in learning more about this topic. Thank you for your assistance, I appreciate it greatly!

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• Another floating point question

  - by jeffmax329

  I have read most of the posts on here regarding floating point, and I understand the basic underlying issue that using IEEE 754 (and just by the nature of storing numbers in binary) certain fractions cannot be represented. I am trying to figure out the following: If both Python and JavaScript use the IEEE 754 standard, why is it that executing the following in Python .1 + .1 Results in 0.20000000000000001 (which is to be expected) Where as in Javascript (in at least Chrome and Firefox) the answer is .2 However performing .1 + .2 In both languages results in 0.30000000000000004 In addition, executing var a = 0.3; in JavaScript and printing a results in 0.3 Where as doing a = 0.3 in Python results in 0.29999999999999999 I would like to understand the reason for this difference in behavior. In addition, many of the posts on OS link to a JavaScript port of Java's BigDecimal, but the link is dead. Does anyone have a copy?

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• Switch to BigInteger if necessary

  - by fahdshariff

  I am reading a text file which contains numbers in the range [1, 10^100]. I am then performing a sequence of arithmetic operations on each number. I would like to use a BigInteger only if the number is out of the int/long range. One approach would be to count how many digits there are in the string and switch to BigInteger if there are too many. Otherwise I'd just use primitive arithmetic as it is faster. Is there a better way? Is there any reason why Java could not do this automatically i.e. switch to BigInteger if an int was too small? This way we would not have to worry about overflows.

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• Why a thread is aborted in ASP.NET MVC (again)?

  - by Dario Solera

  Here is what I do in a controller action: create and start a new Thread that does a relatively long processing task (~30 seconds on average, but might be several minutes) immediately return the page response so the user knows processing has started (trivially, a Json with a task ID for polling purposes). At some random point, ThreadAbortException is thrown, so the async task does not complete. The exception is not thrown every time, it just happens randomly roughly 25% of the times. Points to note: I'm not calling Response.End or Response.Redirect - there isn't even a request running when the exception is thrown I tried using ThreadPool and I got the same behavior I know running threads in ASP.NET has several caveats but I don't care right now Any suggestion?

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• mkmapview cpu usage on iphone 3G

  - by mozveren

  Hello all, I have some troubles with iphone 3G and Mkmapview. After a certain random time, my application freeze. When I launch with performances tool, I can see that the application a lot of time to retrieve map tiles in cache. 19.6 7006 Foundation +[NSURLConnection(NSURLConnectionReallyInternal) 18.5 6613 GMM GMM::TileCachePrivate::runCacheThread() Its seems that the MkMapView component launch several threads to load the tiles in caches. How I can avoid this behavior ? The behavior seems to not make troubles on 3GS. Thanks

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• How to split strings at specific intervals to arrays in javascript

  - by t3st

  how to split strings at specific interveals to arrays in javascript for example: split this string into 4 characters (including space and characters) this is an example should be split,numbers(123),space,characters also included to this ------> 1st array is ------> 2nd array an ------> 3rd array exam ------> 4th array ple ------> 5th array shou ------> 6th array ............ etc till..... ..ed ------> last array

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• How do I get a preference to correlate to a variable?

  - by Dan T

  I have my menu button bringing up a Settings option, which brings up numerous ListPreferences such as weight and various sizes for glasses (it's a BAC calculator app). I'll pick one example... weight will work. Depending on how much you weigh it will affect your BAC. I have a int for Weight, set at 180. I would like someone to be able to go into the menu Settings, pick the "Weight" ListPreference, and choose between 100, 130, 150, 180, 210, 240, 270, and 300. I already have the numbers show up (all of the arrays have been created) and I can choose one, but it doesn't do anything because it's not linked up with the int Weight variable. How do I go about linking the information?

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• Sql server management studio reporting "The semaphore timeout period has expired."

  - by nis-simonsen

  On our development sql server, executing any query containing more than approximately 700 characters stalls for about 10 seconds and then reports the following error: Msg 121, Level 20, State 0, Line 0 A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 - The semaphore timeout period has expired.) for example, this query select * from FooTable where id = ' (.. and then 700 spaces ..) ' fails fails with the timeout error while this one select * from FooTable where id = ' (.. and then 600 spaces ..) ' fails with the expected Msg 8169, Level 16, State 2, Line 1 Conversion failed when converting from a character string to uniqueidentifier. - immediately. Indeed, throwing any query, including random garbage at our dev sql server exhibits this behaviour, while any other sql server I have available acts as expected, so I would think that the query never actually gets to parsing on the server. I'm at a loss here - any hints?

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• How do I select a fixed number of rows for each group?

  - by Maiasaura

  Here is some example data in a mysql table a b distance 15 44 250 94 31 250 30 41 250 6 1 250 95 18 250 72 84 500 14 23 500 55 24 500 95 8 500 59 25 500 40 73 500 65 85 500 32 50 500 31 39 500 22 25 500 37 11 750 98 39 750 15 57 750 9 22 750 14 44 750 69 22 750 62 50 750 89 35 750 67 65 750 74 37 750 52 36 750 66 53 750 82 74 1000 79 22 1000 98 41 1000 How do I query this table such that I get 2 rows per distance selected at random? A successful query will produce something like a b distance 30 41 250 95 18 250 59 25 500 65 85 500 15 57 750 89 35 750 79 22 1000 98 41 1000

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• Excel plugin: Finding a Chart's Source Data Number Format String

  - by Jack

  I'm currently working on a plugin for excel (using VB.net--not VBA) that will attempt (among other things) to recognize the format of the source data of a chart and configure the chart's series' number format strings appropriately. That is, yearly data should always be two numbers, monthly data should always be a 3-letter month followed by a 2-digit year, etc. The goal is to have a uniform representation across all charts for monthly data, annual data, daily data, etc. My question is this: how do I find the number format string for the cells (or any cell that is part of that series, as I will be assuming all cells that make up a particular series have the same format) that represent the source data for the chart? Note: I can assume that the chart will always point to a range of cells (not, for example, an array of data).

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• Propel: How the "Affected Rows" Returned from doUpdate is defined

  - by Ngu Soon Hui

  In propel there is this doUpdate function, that will return the numbers of affected rows by this query. The question is, if there is no need to update the row ( because the set value is already the same as the field value), will those rows counted as the affected row? Take for example, I have the following table: ID | Name | Books 1 | S1oon | Me 2 | S1oon | Me Let's assume that I write a ORM function of the equivalent of the following query: update `new table` set Books='Me' where Name='S1oon'; What will the doUpdate result return? Will it return 0 ( because all the Books column are already Me, hence there is no need to update), or will it be 2 ( because there are 2 rows that fulfill the where condition) ?

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• HOw Do I update from table-2 to table-1

  - by mathew

  HI what is the wrong in this code?? i have set it 24 hours to update the value in the table.but the problem is if $row is empty then it inserts value from table-2 but after 24 hours it wont update the value. what I want is it must delete the existing value and insert new one(random value) or it must update the same $row with new value what ever... if ($row == 0){ mysql_query("INSERT INTO table-1 (regtime,person,location,address,rank,ip,geocode) SELECT NOW(),person,location,address,rank,ip,geocode FROM table-2 ORDER BY RAND() LIMIT 1");}else{ mysql_query("UPDATE table-1 SELECT regtime=NOW(), person=person, location=location, address=address, rank=rank, ip=ip, geocode=geocode FROM table-2 ORDER BY RAND() LIMIT 1");}

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• What are good resources for computer graphics basics?

  - by Hanno Fietz

  During Flex programming, I recently ran into several questions (about box models, ways to join lines and misaligning pixels [on doctype]) regarding computer graphics and layout, where I felt that I lacked some basic background on things like concepts like the box model approaches mapping real numbers to a pixel raster (like font anti-aliasing) conventions found across drawing engines, like do you count y coordinates from top or bottom, and why I feel that reading some basic Wikipedia articles, books or tutorials on these subjects might help in phrasing my questions more specifically and debugging my code more systematically. I have repeatedly found myself writing tiny test apps in Flex, just to find out how the APIs do very basic stuff. My assumption would be that if I knew the right vocabulary and some general concepts, I could solve these questions much faster.

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• Invoking different methods on threads

  - by Kraken

  I have a main process main. It creates 10 threads (say) and then what i want to do is the following: while(required){ Thread t= new Thread(new ClassImplementingRunnable()); t.start(); counter++; } Now i have the list of these threads, and for each thread i want to do a set of process, same for all, hence i put that implementation in the run method of ClassImplementingRunnable. Now after the threads have done their execution, i wan to wait for all of them to stop, and then evoke them again, but this time i want to do them serially not in parallel. for this I join each thread, to wait for them to finish execution but after that i am not sure how to evoke them again and run that piece of code serially. Can i do something like for(each thread){ t.reevoke(); //how can i do that. t.doThis(); // Also where does `dothis()` go, given that my ClassImplementingRunnable is an inner class. } Also, i want to use the same thread, i.e. i want the to continue from where they left off, but in a serial manner. I am not sure how to go about the last piece of pseudo code. Kindly help. Working with with java.

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• Error 500 on template.render() with jinja2

  - by Asperitas

  I am working on playing with some Python to create a webapp. At first I put the HTML in a string, using %s to fill certain elements. That all worked perfectly. Now I want to put the HTML in a template, so I followed this tutorial. My code looks like this (I deleted irrelevant code for this error): import codecs import cgi import os import jinja2 jinja_environment = jinja2.Environment(loader=jinja2.FileSystemLoader(os.path.join(os.path.dirname(__file__)))) class Rot13Handler(webapp2.RequestHandler): def get(self): template = jinja_environment.get_template('rot13.html') self.response.out.write(template.render({'text': ''})) When I replace just template.render({'text': ''}) a random string, the program works fine. I did add the latest jinja2 library to my app.yaml, and naturally my rot13.html does exist with the {{ text }} added. So could anyone please help me in the right direction? I don't know why it's going wrong.

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• Scanning FedEx labels into a visual basic program

  - by 0bfus

  I have a program that has tracking numbers entered into it and it stores them in a database and i would like to add a scanner to the mix. The scanner is acting like a keyboard and scannes just fine, the problem is scanning a FedEx number gives a 32 digit number and i am only iterested in the tracking number portion of it. I saw an example on the web for an excel macro and tried to modify it but it doesnt seem to work. Is there something i could do to just get the 12 digit number? This is what it looks like so far. Any help would be greatly appreciated. With BarcodeText If .Text < "1z99999999999999999" Then .Text = Mid(.Text, 17, 12) End If

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• Delphi: How to avoid EIntOverflow underflow when subtracting?

  - by Ian Boyd

  Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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• What are "named tuples" in Python?

  - by Denilson Sá

  Reading the changes in Python 3.1, I found something... unexpected: The sys.version_info tuple is now a named tuple: I never heard about named tuples before, and I thought elements could either be indexed by numbers (like in tuples and lists) or by keys (like in dicts). I never expected they could be indexed both ways. Thus, my questions are: What are named tuples? How to use them? Why/when should I use named tuples instead of normal tuples? Why/when should I use normal tuples instead of named tuples? Is there any kind of "named list" (a mutable version of the named tuple)?

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• Is there a name for this type of algorithm?

  - by rehanift

  I have a 2 dimensional array forming a table: [color][number][shape ] ------------------------- [black][10 ][square ] [black][10 ][circle ] [red ][05 ][triangle] [red ][04 ][triangle] [green][11 ][oval ] and what I want to do is group largest common denominators, such that we get: 3 groups group #1: color=black, number=10, shapes = [square, circle] group #2: color=red, shape=triange, numbers = [05,04] group #3: color=green, number=11, shape = oval I wrote code that will handle a 2 "column" scenario, then I needed to adjusted it for 3 and I was figuring I might as well do it for n. I wanted to check first if there is some literature around this but I can't think of what to start looking for!

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• Problems with dynamic programming

  - by xan

  I've got difficulties with understanding dynamic programming, so I decided to solve some problems. I know basic dynamic algorithms like longest common subsequence, knapsack problem, but I know them because I read them, but I can't come up with something on my own :-( For example we have subsequence of natural numbers. Every number we can take with plus or minus. At the end we take absolute value of this sum. For every subsequence find the lowest possible result. in1: 10 3 5 4; out1: 2 in2: 4 11 5 5 5; out2: 0 in3: 10 50 60 65 90 100; out3: 5 explanation for 3rd: 5 = |10+50+60+65-90-100| what it worse my friend told me that it is simple knapsack problem, but I can't see any knapsack here. Is dynamic programming something difficult or only I have big problems with it?

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• Color blindness: Are you aware of it? Do you design for it?

  - by User

  I'm curious whether many of us who do design or take design decisions have ever heard of this problem. I'm aware there are dangerous color combinations, like green + red. This is probably one of the most popular cases of color blindness. If you have green text on a red background and vice versa some people won't see anything. I've also seen in practice that green text on a blue background was not seen by one guy. What other color compositions should be avoided, and how often these cases are to be expected? Let us make some ranging by encounter probability who has the numbers. Addition: I've just remembered one very bad example that causes problems to just about everyone - blue text on a black background. It's unreadable for all intents and purposes. Never could understand what could possibly compel a web master to use this color combination...

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• Overloaded function print

  - by Olga Shirokova

  For one of the assignments I need to create an overloaded function print that prints an element or all elements of an array. I have no problem with printing the entire array: for( int i = 0; i < size; i++) cout << list [ i ] <<endl; But how do I make the same function to print only one particular element? The way I see it is to ask a user what to print, either one element or all numbers. Or am I missing something here?

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• sort giving strange results

  - by Jay

  I have an array of email addresses that I am trying to sort, but I'm getting odd results. Here is what I mean: sort($array); print_r($array); ...[79] => 91******@******.com [80] => 9l***@**********.com [81] => ps*******@**********.com [82] => a.c******@*****.com [83] => a.d****@*****.com... What would cause that email beginning with p's to be mixed in after the numbers and before the A's? I removed that email address from the database and replaced it with "testing" and then "testing" appeared in the same position.

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• How do I get a preference to correlate to variable?

  - by Dan T

  I have my menu button bringing up a Settings option, which brings up numerous ListPreferences such as weight and various sizes for glasses (it's a BAC calculator app). I'll pick one example... weight will work. Depending on how much you weigh it will affect your BAC. I have a int for Weight, set at 180. I would like someone to be able to go into the menu Settings, pick the "Weight" ListPreference, and choose between 100, 130, 150, 180, 210, 240, 270, and 300. I already have the numbers show up (all of the arrays have been created) and I can choose one, but it doesn't do anything because it's not linked up with the int Weight variable. How do I go about linking the information?

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