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  • design a model for a system of dependent variables

    - by dbaseman
    I'm dealing with a modeling system (financial) that has dozens of variables. Some of the variables are independent, and function as inputs to the system; most of them are calculated from other variables (independent and calculated) in the system. What I'm looking for is a clean, elegant way to: define the function of each dependent variable in the system trigger a re-calculation, whenever a variable changes, of the variables that depend on it A naive way to do this would be to write a single class that implements INotifyPropertyChanged, and uses a massive case statement that lists out all the variable names x1, x2, ... xn on which others depend, and, whenever a variable xi changes, triggers a recalculation of each of that variable's dependencies. I feel that this naive approach is flawed, and that there must be a cleaner way. I started down the path of defining a CalculationManager<TModel> class, which would be used (in a simple example) something like as follows: public class Model : INotifyPropertyChanged { private CalculationManager<Model> _calculationManager = new CalculationManager<Model>(); // each setter triggers a "PropertyChanged" event public double? Height { get; set; } public double? Weight { get; set; } public double? BMI { get; set; } public Model() { _calculationManager.DefineDependency<double?>( forProperty: model => model.BMI, usingCalculation: (height, weight) => weight / Math.Pow(height, 2), withInputs: model => model.Height, model.Weight); } // INotifyPropertyChanged implementation here } I won't reproduce CalculationManager<TModel> here, but the basic idea is that it sets up a dependency map, listens for PropertyChanged events, and updates dependent properties as needed. I still feel that I'm missing something major here, and that this isn't the right approach: the (mis)use of INotifyPropertyChanged seems to me like a code smell the withInputs parameter is defined as params Expression<Func<TModel, T>>[] args, which means that the argument list of usingCalculation is not checked at compile time the argument list (weight, height) is redundantly defined in both usingCalculation and withInputs I am sure that this kind of system of dependent variables must be common in computational mathematics, physics, finance, and other fields. Does someone know of an established set of ideas that deal with what I'm grasping at here? Would this be a suitable application for a functional language like F#? Edit More context: The model currently exists in an Excel spreadsheet, and is being migrated to a C# application. It is run on-demand, and the variables can be modified by the user from the application's UI. Its purpose is to retrieve variables that the business is interested in, given current inputs from the markets, and model parameters set by the business.

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  • iphone global variables accessed from different views

    - by Rob
    Okay, so ultimately I want a program where the user can input simple data such as their name, date of birth, address, etc. and then have that information stay through multiple views. I am having the user input their information as UITextFields but their are multiple views that they are using to input the data. Is there a way that when the user inputs data in a UITextField - then moves to another view - then returns to the original view - that the data will still be in that UITextField? I figure since there are placeholders that there must be a command to show previously written text in that field when the viewController is called. Also, for the life of me, I can't figure out how to keep these variables global. I have read in multiple areas that I should define them in the AppDelegate as a simple: NSString *userName; NSString *userDOB; But how do I assign the strings from the UITextFields in a different view to these variables and then re-assign them to the UITextFields when the user returns to the place where they originally input them? (I apologize if I am not explaining this coherently - I am a bit of a newb)

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  • Sharing runtime variables between files

    - by nightcracker
    I have a project with a few files that all include the header global.hpp. Those files want to share and update information that is relevant for the whole program during runtime (that data is gathered progressively during the program runs but the fields of data are known at compile-time). Now my idea was to use a struct like this: global.hpp #include <string> #ifndef _GLOBAL_SESSION_STRUCT #define _GLOBAL_SESSION_STRUCT struct session_struct { std::string username; std::string password; std::string hostname; unsigned short port; // more data fields as needed }; #endif extern struct session_struct session; main.cpp #include "global.hpp" struct session_struct session; int main(int argc, char* argv[]) { session.username = "user"; session.password = "secret"; session.hostname = "example.com"; session.port = 80; // other stuff, etc return 0; } Now every file that includes global.hpp can just read & write the fields of the session struct and easily share information. Is this the correct way to do this? NOTE: For this specific project no threading is used. But please (for future projects and other people reading) clarify in your answer how this (or your proposed) solution works when threaded. Also, for this example/project session variables are shared. But this should also apply to any other form of shared variables.

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  • php request variables assigning $_GEt

    - by chris
    if you take a look at a previous question http://stackoverflow.com/questions/2690742/mod-rewrite-title-slugs-and-htaccess I am using the solution that Col. Shrapnel proposed- but when i assign values to $_GET in the actual file and not from a request the code doesnt work. It defaults away from the file as if the $_GET variables are not set The code I have come up with is- if(!empty($_GET['cat'])){ $_GET['target'] = "category"; if(isset($_GET['page'])){ $_GET['pageID'] = $_GET['page']; } $URL_query = "SELECT category_id FROM cats WHERE slug = '".$_GET['cat']."';"; $URL_result = mysql_query($URL_query); $URL_array = mysql_fetch_array($URL_result); $_GET['category_id'] = $URL_array['category_id']; }elseif($_GET['product']){ $_GET['target'] = "product"; $URL_query = "SELECT product_id FROM products WHERE slug = '".$_GET['product']."';"; $URL_result = mysql_query($URL_query); $URL_array = mysql_fetch_array($URL_result); print_r($URL_array); $_GET['product_id'] = $URL_array['product_id']; The original variable string that im trying to represent is /cart.php?Target=product&product_id=16142&category_id=249 And i'm trying to build the query string variables with code and including cart.php so i can use cleaner URL's So I have product/product-title-with-clean-url/ going to slug.php?product=slug Then the slug searches the db for a record with the matching slug and returns the product_id as in the code above.Then built the query string and include cart.php

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  • C: Global ,Static variables understanding

    - by pavun_cool
    Hi All, In following program . I have one doubt. I have declared one global variable . I am printing the address of the global variable in the function . It is giving me same address when I am not changing the value of global . If I did any changes in the global variables It is giving me different address why...........? Like that it is happening for static also. #include<stdio.h> int global=10 ; // Global variables void function(); main() { global=20; printf ( " %p \n" , global ) ; printf ( " Val: %d\n", global ) ; function(); new(); } void function() { global=30; printf ( " %p \n" , global ) ; printf ( " Val: %d\n", global ) ; } Thanks.

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  • Prolog singleton variables in Python

    - by Rubens
    I'm working on a little set of scripts in python, and I came to this: line = "a b c d e f g" a, b, c, d, e, f, g = line.split() I'm quite aware of the fact that these are decisions taken during implementation, but shouldn't (or does) python offer something like: _, _, var_needed, _, _, another_var_needed, _ = line.split() as well as Prolog does offer, in order to exclude the famous singleton variables. I'm not sure, but wouldn't it avoid unnecessary allocation? Or creating references to the result of the split call does not count up as overhead? EDIT: Sorry, my point here is: in Prolog, as far as I'm concerned, in an expression like: test(L, N) :- test(L, 0, N). test([], N, N). test([_|T], M, N) :- V is M + 1, test(T, V, N). The variable represented by _ is not accessible, for what I suppose the reference to the value that does exist in the list [_|T] is not even created. But, in Python, if I use _, I can use the last value assigned to _, and also, I do suppose the assignment occurs for each of the variables _ -- which may be considered an overhead. My question here is if shouldn't there be (or if there is) a syntax to avoid such unnecessary attributions.

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  • MYSQL variables - SET @var

    - by Lizard
    I am attempting to create a mysql snippet that will analyse a table and remove duplicate entries (duplicates are based on two fields not entire record) I have the following code that works when I hard code the variables in the queries, but when I take them out and put them as variables I get mysql errors, below is the script SET @tblname = 'mytable'; SET @fieldname = 'myfield'; SET @concat1 = 'checkfield1'; SET @concat2 = 'checkfield2'; ALTER TABLE @tblname ADD `tmpcheck` VARCHAR( 255 ) NOT NULL; UPDATE @tblname SET `tmpcheck` = CONCAT(@concat1,'-',@concat2); CREATE TEMPORARY TABLE `tmp_table` ( `tmpfield` VARCHAR( 100 ) NOT NULL ) ENGINE = MYISAM ; INSERT INTO `tmp_table` (`tmpfield`) SELECT @fieldname FROM @tblname GROUP BY `tmpcheck` HAVING ( COUNT(`tmpcheck`) > 1 ); DELETE FROM @tblname WHERE @fieldname IN (SELECT `tmpfield` FROM `tmp_table`); ALTER TABLE @tblname DROP `tmpcheck`; I am getting the following error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '@tblname ADD `tmpcheck` VARCHAR( 255 ) NOT NULL' at line 1 Is this because I can't use a variable for a table name? What else could be wrong or how wopuld I get around this issue. Thanks in adavnce

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  • httpd.conf variables : What is the difference between ${var} and %{var}?

    - by 108.im
    What is the difference between ${var} and %{var} in httpd.conf? How and when would one use ${} and %{}? http://httpd.apache.org/docs/2.4/configuring.html mentions : The values of variables defined with the Define of or shell environment variables can be used in configuration file lines using the syntax ${VAR}. http://httpd.apache.org/docs/2.4/mod/mod_rewrite.html mentions: Server-Variables:These are variables of the form %{ NAME_OF_VARIABLE } and RewriteMap expansions:These are expansions of the form ${mapname:key|default}. Will ${VAR} be used everywhere in httpd.conf, except in mod_rewrite directive's (like RewriteCond, RewriteRule but except for RewriteMap expansions which use ${} as in RewriteRule ^/ex/(.*) ${examplemap:$1} ) Would a variable set in httpd.conf using SetEnvIf Directive, for use in same httpd.conf, be used as ${var} except when the variable is used with mod_rewrite directive's, where the variable would be used as %{var}?

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  • How can I set environment variables for a graphical login on linux?

    - by Ryan Thompson
    I'm looking for a way to set arbitrary environment variables for my graphical login on linux. I am not talking about starting a terminal and exporting environment variables within the terminal, because those variables only exist within that one terminal. I want to know how to set an environment variable that will apply to all programs started in my graphical session. In other words, what's the Xorg equivalent of ~/.bash_login?

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  • Over-Current condition on port 7 or 8

    - by Dymatic
    I am having a problem with my USB ports. It shows over-current conditions on ports 7 and 8. I have heard that this is caused by a damaged USB port, and since it is detecting it on two ports it seems that I have two that are broken. I do indeed have two that do not work, so that is not the issue. What I would like to do is disable whatever program is running over-current condition checks. tty's are unusable at this point. Every few second a new over-current condition occurs. Here is the output of dmesg: http://pastebin.com/CuFKRGue Is there an easy way to disable these checks or damage the ports to a point where it will no longer check? Fixing them is not important or an option.

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  • Wait on multiple condition variables on Linux without unnecessary sleeps?

    - by Joseph Garvin
    I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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  • xcode global variables

    - by Apache
    hi experts, how to get xcode variables result from one view controller to another view controller, actually in one view controller i called web services to get userID which is declare as NSString, and in another view controller i want to display the userID which is retrieve from previous view controller, so how this can be done thanks

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  • Declaring variables with New DataSet vs DataSet

    - by eych
    What is the impact of creating variables using: Dim ds as New DataSet ds = GetActualData() where GetActualData() also creates a New DataSet and returns it? Does the original empty DataSet that was 'New'ed just get left in the Heap? What if this kind of code was in many places? Would that affect the ASP.NET process and cause it to recycle sooner?

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  • AJAX function to POST 4 variables

    - by kirgy
    Ive been having great frustration for hours now trying to remember my AJAX! Im trying to write a function which will be called that will simply POST 4 variables to a given URL, written in javascript and not jquery such as: function postVariables(URL, var1, var2, var3, var4) { ...... return true; } Can anyone help?

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  • Struts2, problem with 2 variables in one address.

    - by tzim
    Hi. I'm using struts2, now in my jsp file i've got 2 variables: ${server_address} ${pageContext.request.contextPath} Now i want to connect it in my tag: <s:form action="%{server_address}%{pageContext.request.contextPath}/actionName.action"> But generated output looks like that: <form method="post" action="http://10.0.0.5:8088/actionName.action" name="actionName" id="actionName"> There is no contextPath... How can i connect this two variable ?

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  • how to pass structure variables

    - by deep
    Am having a set of structure variable in one form, i want to use that structure variable as a global variables. i need to use those structure variable in through out my whole application, how to use structure as global variable??

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  • define colors as variables in CSS

    - by patrick
    Hi all, I'm working CSS file which is quite long. I know the client could ask for changes to the color scheme, and was wondering: is it possible to assign colors to variables so I can just change them to have the new color applied to all elements that use it? Please note I can't use php to dynamically change the css file.

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  • When are global variables acceptable?

    - by dsimcha
    Everyone here seems to hate global variables, but I see at least one very reasonable use for them: They are great for holding program parameters that are determined at program initialization and not modified afterwords. Do you agree that this is an exception to the "globals are evil" rule? Is there any other exception that you can think of, besides in quick and dirty throwaway code where basically anything goes? If not, why are globals so fundamentally evil that you do not believe that there are any exceptons?

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