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  • AbsoluteTime with numeric argument behaves strangely.

    - by dreeves
    This is strange: DateList@AbsoluteTime[596523] returns {2078, 7, 2, 2, 42, 9.7849} But DateList@AbsoluteTime[596524] returns {1942, 5, 26, 20, 28, 39.5596} The question: What's going on? Note that AbsoluteTime with a numeric argument is undocumented. (I think I now know what it's doing but figured this is useful to have as a StackOverflow question for future reference; and I'm curious if there's some reason for that magic 596523 number.) PS: I encountered this when writing these utility functions for converting to and from unix time in Mathematica: (* Using Unix time (an integer) instead of Mathematica's AbsoluteTime... *) tm[x___] := AbsoluteTime[x] (* tm is an alias for AbsoluteTime. *) uepoch = tm[{1970}, TimeZone->0]; (* unixtm works analogously to tm. *) unixtm[x___] := Round[tm[x]-uepoch] (* tm & unixtm convert between unix & *) unixtm[x_?NumericQ] := Round[x-uepoch] (* mma epoch time when given numeric *) tm[t_?NumericQ] := t+uepoch (* args. Ie, they're inverses. *)

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  • Nested WHILE loops not acting as expected - Javascript / Google Apps Script

    - by dthor
    I've got a function that isn't acting as intended. Before I continue, I'd like preface this with the fact that I normally program in Mathematica and have been tasked with porting over a Mathematica function (that I wrote) to JavaScript so that it can be used in a Google Docs spreadsheet. I have about 3 hours of JavaScript experience... The entire (small) project is calculating the Gross Die per Wafer, given a wafer and die size (among other inputs). The part that isn't working is where I check to see if any corner of the die is outside of the effective radius, Reff. The function takes a list of X and Y coordinates which, when combined, create the individual XY coord of the center of the die. That is then put into a separate function "maxDistance" that calculates the distance of each of the 4 corners and returns the max. This max value is checked against Reff. If the max is inside the radius, 1 is added to the die count. // Take a list of X and Y values and calculate the Gross Die per Wafer function CoordsToGDW(Reff,xSize,ySize,xCoords,yCoords) { // Initialize Variables var count = 0; // Nested loops create all the x,y coords of the die centers for (var i = 0; i < xCoords.length; i++) { for (var j = 0; j < yCoords.length, j++) { // Add 1 to the die count if the distance is within the effective radius if (maxDistance(xCoords[i],yCoords[j],xSize,ySize) <= Reff) {count = count + 1} } } return count; } Here are some examples of what I'm getting: xArray={-52.25, -42.75, -33.25, -23.75, -14.25, -4.75, 4.75, 14.25, 23.75, 33.25, 42.75, 52.25, 61.75} yArray={-52.5, -45.5, -38.5, -31.5, -24.5, -17.5, -10.5, -3.5, 3.5, 10.5, 17.5, 24.5, 31.5, 38.5, 45.5, 52.5, 59.5} CoordsToGDW(45,9.5,7.0,xArray,yArray) returns: 49 (should be 72) xArray={-36, -28, -20, -12, -4, 4, 12, 20, 28, 36, 44} yArray={-39, -33, -27, -21, -15, -9, -3, 3, 9, 15, 21, 27, 33, 39, 45} CoordsToGDW(32.5,8,6,xArray,yArray) returns: 39 (should be 48) I know that maxDistance() is returning the correct values. So, where's my simple mistake? Also, please forgive me writing some things in Mathematica notation... Edit #1: A little bit of formatting. Edit #2: Per showi, I've changed WHILE loops to FOR loops and replaced <= with <. Still not the right answer. It did clean things up a bit though... Edit #3: What I'm essentially trying to do is take [a,b] and [a,b,c] and return [[a,a],[a,b],[a,c],[b,a],[b,b],[b,c]]

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  • Add gridlines to a output plot in Mathemaitca

    - by xslittlegrass
    I'm trying to add gridlines to a output density plot in Mathematica. The plot is generated by a long calculation in Mathematica and when I do the plot I forget to add the Mesh-True options. I don't want to do all the calculation and generate the plot again since it takes a long time. Is that possible to add the gridlines or mesh lines to plot ONLY using the output plot at hand? For example, If I have a plot p. Is it possible to add the mesh lines ONLY manipulate p? In a ordinary one dimensional plot, this will work p1 = Plot[Sin[x], {x, -3, 3}]; Insert[p1, GridLines -> Automatic, -1] But when I try the density plot, it seems the gridlines is always under the plot, and can be seen only at the image margin area. p2 = DensityPlot[Sin[x + y^2], {x, -3, 3}, {y, -2, 2}, PlotRangePadding -> 0.2]; Insert[p2, GridLines -> Automatic, -1] Updata The Mesh option on the output plot will not work because Mesh is not a options of a Graphics: Show[p2,Mesh->True] will give a message "an unrecoginzed option name(Mesh) was encountered while rendering a Graphics" Thanks.

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  • CodeIgniter & Datamapper as frontend, Django Admin as backend, database tables inconsistent

    - by Rasiel
    I created a database for a site i'm doing using Django as the admin backend. However because the server where the site is hosted on, won't be able to support Python, I find myself needing to do the front end in PHP and as such i've decided to use CodeIgniter along with Datamapper to map the models/relationship. However DataMapper requires the tables to be in a specific format for it to work, and Django maps its tables differently, using the App name as the prefix in the table. I've tried using the prefix & join_prefix vars in datamapper but still doesn't map them correctly. Has anyone used a combination of this? and if so how have the fixed the issue of db table names being inconsistent? Is there anything out there that i can use to make them work together?

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  • JPA IndirectSet changes not reflected in Spring frontend

    - by Jon
    I'm having an issue with Spring JPA and IndirectSets. I have two entities, Parent and Child, defined below. I have a Spring form in which I'm trying to create a new Child and link it to an existing Parent, then have everything reflected in the database and in the web interface. What's happening is that it gets put into the database, but the UI doesn't seem to agree. The two entities that are linked to each other in a OneToMany relationship like so: @Entity @Table(name = "parent", catalog = "myschema", uniqueConstraints = @UniqueConstraint(columnNames = "ChildLinkID")) public class Parent { private Integer id; private String childLinkID; private Set<Child> children = new HashSet<Child>(0); @Id @GeneratedValue(strategy = IDENTITY) @Column(name = "id", unique = true, nullable = false) public Integer getId() { return this.id; } public void setId(Integer id) { this.id = id; } @Column(name = "ChildLinkID", unique = true, nullable = false, length = 6) public String getChildLinkID() { return this.childLinkID; } public void setChildLinkID(String childLinkID) { this.childLinkID = childLinkID; } @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "parent") public Set<Child> getChildren() { return this.children; } public void setChildren(Set<Child> children) { this.children = children; } } @Entity @Table(name = "child", catalog = "myschema") public class Child extends private Integer id; private Parent parent; @Id @GeneratedValue(strategy = IDENTITY) @Column(name = "id", unique = true, nullable = false) public Integer getId() { return this.id; } public void setId(Integer id) { this.id = id; } @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "ChildLinkID", referencedColumnName = "ChildLinkID", nullable = false) public Parent getParent() { return this.parent; } public void setParent(Parent parent) { this.parent = parent; } } And of course, assorted simple properties on each of them. Now, the problem is that when I edit those simple properties from my Spring interface, everything works beautifully. I can persist new entities of these types and they'll appear when using the JPATemplate to do a find on, say, all Parents (getJpaTemplate().find("select p from Parent p")) or on individual entities by ID or another property. The problem I'm running into is that now, I'm trying to create a new Child linked to an existing Parent through a link from the Parent's page. Here's the important bits of the Controller (note that I've placed the JPA foo in the controller here to make it clearer; the actual JpaDaoSupport is actually in another class, appropriately tiered): protected Object formBackingObject(HttpServletRequest request) throws Exception { String parentArg = request.getParameter("parent"); int parentId = Integer.parseInt(parentArg); Parent parent = getJpaTemplate().find(Parent.class, parentId); Child child = new Child(); child.setParent(parent); NewChildCommand command = new NewChildCommand(); command.setChild(child); return command; } protected ModelAndView onSubmit(Object cmd) throws Exception { NewChildCommand command = (NewChildCommand)cmd; Child child = command.getChild(); child.getParent().getChildren().add(child); getJpaTemplate().merge(child); return new ModelAndView(new RedirectView(getSuccessView())); } Like I said, I can run through the form and fill in the new values for the Child -- the Parent's details aren't even displayed. When it gets back to the controller, it goes through and saves it to the underlying database, but the interface never reflects it. Once I restart the app, it's all there and populated appropriately. What can I do to clear this up? I've tried to call extra merges, tried refreshes (which gave a transaction exception), everything short of just writing my own database access code. I've made sure that every class has an appropriate equals() and hashCode(), have full JPA debugging on to see that it's making appropriate SQL calls (it doesn't seem to make any new calls to the Child table) and stepped through in the debugger (it's all in IndirectSets, as expected, and between saving and displaying the Parent the object takes on a new memory address). What's my next step?

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  • Magento frontend and backend page looks different

    - by itsandy
    Hi All, I am a newb in magento and recently started looking at it to create a store for my client. I am not sure but i tried installing firephp extension and soon after that I’m having my screen looks like the screenshot. ** please check the link provided! Do I have to make any installations to get everything working as normal or what am I suppose to do to go to the normal screen. I have also changed the inline translation option to NO if thats what it requires. Any help would be appreciated. Cheers I have also posted this question on the magento forum http://www.magentocommerce.com/boards/viewthread/193499/

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  • Should frontend and backend handled by different controllers?

    - by DR
    In my previous learning projects I always used a single controller, but know I wonder if that is good practice or even always possible. In all RESTful Rails tutorials the controllers have a show, an edit and an index view. If an authorized user is logged on, the edit view becomes available and the index view shows additional data manipulation controls, like a delete button or a link to the edit view. Now I have a Rails application which falls exactly into this pattern, but the index view is not reusable: The normal user sees a flashy index page with lots of pictures, complex layout, no Javascript requirement, ... The Admin user index has a completly different minimalistic design, jQuery table and lots of additional data, ... Now I'm not sure how to handle this case. I can think of the following: Single controller, single view: The view is split into two large blocks/partials using an if statement. Single controller, two views: index and index_admin. Two different controllers: BookController and BookAdminController None of this solutions seems perfect, but for now I'm inclined to use the 3rd option. What's the preferred way to do this?

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  • Frontend Intertag Communication

    - by Matt
    Hey all, I've had a question that I've been wondering for a while. I'm making a templating system for front-ends where tags are interpretted (like Smarty). I was wondering if there is value in having the tags be able to communicate with the HTML document and other "Smartyish" tags. I was hoping that the community would have some thoughts on this situation. Benefits: More power (tags can tell other tags how to look) Better structure (smartyish tags behave and look just like html tags) Tags can manipulate any element on the page Drawbacks: Tags can manipulate any element on the page Tags can interfere with other tags Code time will increase

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  • PHP, MySQL, jQuery, AJAX: json data returns correct response but frontend returns error

    - by Devner
    Hi all, I have a user registration form. I am doing server side validation on the fly via AJAX. The quick summary of my problem is that upon validating 2 fields, I get error for the second field validation. If I comment first field, then the 2nd field does not show any error. It has this weird behavior. More details below: The HTML, JS and Php code are below: HTML FORM: <form id="SignupForm" action=""> <fieldset> <legend>Free Signup</legend> <label for="username">Username</label> <input name="username" type="text" id="username" /><span id="status_username"></span><br /> <label for="email">Email</label> <input name="email" type="text" id="email" /><span id="status_email"></span><br /> <label for="confirm_email">Confirm Email</label> <input name="confirm_email" type="text" id="confirm_email" /><span id="status_confirm_email"></span><br /> </fieldset> <p> <input id="sbt" type="button" value="Submit form" /> </p> </form> JS: <script type="text/javascript"> $(document).ready(function() { $("#email").blur(function() { var email = $("#email").val(); var msgbox2 = $("#status_email"); if(email.length > 3) { $.ajax({ type: 'POST', url: 'check_ajax2.php', data: "email="+ email, dataType: 'json', cache: false, success: function(data) { if(data.success == 'y') { alert('Available'); } else { alert('Not Available'); } } }); } return false; }); $("#confirm_email").blur(function() { var confirm_email = $("#confirm_email").val(); var email = $("#email").val(); var msgbox3 = $("#status_confirm_email"); if(confirm_email.length > 3) { $.ajax({ type: 'POST', url: 'check_ajax2.php', data: 'confirm_email='+ confirm_email + '&email=' + email, dataType: 'json', cache: false, success: function(data) { if(data.success == 'y') { alert('Available'); } else { alert('Not Available'); } } , error: function (data) { alert('Some error'); } }); } return false; }); }); </script> PHP code: <?php //check_ajax2.php if(isset($_POST['email'])) { $email = $_POST['email']; $res = mysql_query("SELECT uid FROM members WHERE email = '$email' "); $i_exists = mysql_num_rows($res); if( 0 == $i_exists ) { $success = 'y'; $msg_email = 'Email available'; } else { $success = 'n'; $msg_email = 'Email is already in use.</font>'; } print json_encode(array('success' => $success, 'msg_email' => $msg_email)); } if(isset($_POST['confirm_email'])) { $confirm_email = $_POST['confirm_email']; $email = ( isset($_POST['email']) && trim($_POST['email']) != '' ? $_POST['email'] : '' ); $res = mysql_query("SELECT uid FROM members WHERE email = '$confirm_email' "); $i_exists = mysql_num_rows($res); if( 0 == $i_exists ) { if( isset($email) && isset($confirm_email) && $email == $confirm_email ) { $success = 'y'; $msg_confirm_email = 'Email available and match'; } else { $success = 'n'; $msg_confirm_email = 'Email and Confirm Email do NOT match.'; } } else { $success = 'n'; $msg_confirm_email = 'Email already exists.'; } print json_encode(array('success' => $success, 'msg_confirm_email' => $msg_confirm_email)); } ?> THE PROBLEM: As long as I am validating the $_POST['email'] as well as $_POST['confirm_email'] in the check_ajax2.php file, the validation for confirm_email field always returns an error. With my limited knowledge of Firebug, however, I did find out that the following were the responses when I entered email and confirm_email in the fields: RESPONSE 1: {"success":"y","msg_email":"Email available"} RESPONSE 2: {"success":"y","msg_email":"Email available"}{"success":"n","msg_confirm_email":"Email and Confirm Email do NOT match."} Although the RESPONSE 2 shows that we are receiving the correct message via msg_confirm_email, in the front end, the alert 'Some error' is popping up (I have enabled the alert for debugging). I have spent 48 hours trying to change every part of the code wherever possible, but with only little success. What is weird about this is that if I comment the validation for $_POST['email'] field completely, then the validation for $_POST['confirm_email'] field is displaying correctly without any errors. If I enable it back, it is validating email field correctly, but when it reaches the point of validating confirm_email field, it is again showing me the error. I have also tried renaming success variable in check_ajax2.php page to other different names for both $_POST['email'] and $_POST['confirm_email'] but no success. I will be adding more fields in the form and validating within the check_ajax2.php page. So I am not planning on using different ajax pages for validating each of those fields (and I don't think it's smart to do it that way). I am not a jquery or AJAX guru, so all help in resolving this issue is highly appreciated. Thank you in advance.

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  • change Magento to new server, images of existing product do not shown in frontend

    - by forrest gump
    I have moved a Magento website to a new server to optimize speed. All images appear to be replaced by image placeholders. I tried to set permission for media to 777, when I delete cache media folder and refresh, a new cache folder is created automatically, but only with placeholder images inside. I flushed image cache, reindex in magento backend but still no hope. What should I do now? Somethings might be helpful: . It's fine to create new product with images . Flush cache, only placeholders images are created . tried to use magento-cleanup.php, no hope . tried to remove .htaccess in media folder . the images of products are there in the media folder, just not in cache folder. Magento only looks at the cache folder for image :(

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  • Nginx frontend for AppEngine dev server

    - by benasio
    How to configure nginx for load static ? Static should be given only by the nginx server , everything else nginx + dev_appserver and workingon the same host (localhost or localhost: port) Example request html http://localhost -> nginx -> dev_appserver request static files http://localhost -> nginx

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  • Complex Calculations

    - by mson
    What are the best tools (most efficient) available in .NET (C#) for calculating: integrals partial derivatives other non-trivial math Can people please comment on Mathematica and Matlab and their integration into C#?

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  • Web UI for inputting a function from the reals to the reals, such as a probability distribution.

    - by dreeves
    I would like a web interface for a user to describe a one-dimensional real-valued function. I'm imagining the user being presented with a blank pair of axes and they can click anywhere to create points that are thick and draggable. Double-clicking a point, let's say, makes it disappear. The actual function should be shown in real time as an interpolation of the user-supplied points. Here's what this looks like implemented in Mathematica (though of course I'm looking for something in javascript):

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  • An efficient code to determine if a set is a subset of another set

    - by Edward
    I am looking for an efficient way to determine if a set is a subset of another set in Matlab or Mathematica. Example: Set A = [1 2 3 4] Set B = [4 3] Set C = [3 4 1] Set D = [4 3 2 1] The output should be: Set A Sets B and C belong to set A because A contains all of their elements, therefore, they can be deleted (the order of elements in a set doesn't matter). Set D has the same elements as set A and since set A precedes set D, I would like to simply keep set A and delete set D. So there are two essential rules: 1. Delete a set if it is a subset of another set 2. Delete a set if its elements are the same as those of a preceding set My Matlab code is not very efficient at doing this - it mostly consists of nested loops. Suggestions are very welcome! Additional explanation: the issue is that with a large number of sets there will be a very large number of pairwise comparisons.

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  • posmax: like argmax but gives the position(s) of the element x for which f[x] is maximal

    - by dreeves
    Mathematica has a built-in function ArgMax for functions over infinite domains, based on the standard mathematical definition. The analog for finite domains is a handy utility function. Given a function and a list (call it the domain of the function), return the element(s) of the list that maximize the function. Here's an example of finite argmax in action: http://stackoverflow.com/questions/471029/canonicalize-nfl-team-names/472213#472213 And here's my implementation of it (along with argmin for good measure): (* argmax[f, domain] returns the element of domain for which f of that element is maximal -- breaks ties in favor of first occurrence. *) SetAttributes[{argmax, argmin}, HoldFirst]; argmax[f_, dom_List] := Fold[If[f[#1]>=f[#2], #1, #2]&, First[dom], Rest[dom]] argmin[f_, dom_List] := argmax[-f[#]&, dom] First, is that the most efficient way to implement argmax? What if you want the list of all maximal elements instead of just the first one? Second, how about the related function posmax that, instead of returning the maximal element(s), returns the position(s) of the maximal elements?

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  • An efficient code to determine if a set is a subset of another set

    - by Edward
    I am looking for an efficient way to determine if a set is a subset of another set in Matlab or Mathematica. Example: Set A = [1 2 3 4] Set B = [4 3] Set C = [3 4 1] Set D = [4 3 2 1] The output should be: Set A Sets B and C belong to set A because A contains all of their elements, therefore, they can be deleted (the order of elements in a set doesn't matter). Set D has the same elements as set A and since set A precedes set D, I would like to simply keep set A and delete set D. So there are two essential rules: 1. Delete a set if it is a subset of another set 2. Delete a set if its elements are the same as those of a preceding set My Matlab code is not very efficient at doing this - it mostly consists of nested loops. Suggestions are very welcome! Additional explanation: the issue is that with a large number of sets there will be a very large number of pairwise comparisons.

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  • How to kill slave kernel securely?

    - by Alexey Popkov
    Hello, LinkClose[link] "does not necessarily terminate the program at the other end of the connection" as it is said in the Documentation. Is there a way to kill the process of the slave kernel securely? EDIT: In really I need a function in Mathematica that returns only when the process of the slave kernel has already killed and its memory has already released. Both LinkInterrupt[link, 1] and LinkClose[link] do not wait while the slave kernel exits. At this moment the only such function is seemed to be killProc[procID] function I had showed in one of answers at this page. But is there a built-in analog?

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  • mod_rewrite to nginx rewrite rules

    - by Andrew Bestic
    I have converted most of my Apache HTTPd mod_rewrite rules over to nginx's HttpRewrite module (which calls PHP-FPM via FastCGI on every dynamic request). Simple rules which are defined by hard locations work fine: location = /favicon.ico { rewrite ^(.*)$ /_core/frontend.php?type=ico&file=include__favicon last; } I am still having trouble with regular expressions, which are parsed in mod_rewrite like this (note that I am accepting trailing slashes within the rules, as well as appending the query string to every request): mod_rewrite # File handler RewriteRule ^([a-z0-9-_,+=]+)\.([a-z]+)$ _core/frontend.php?type=$2&file=$1 [QSA,L] # Page handler RewriteRule ^([a-z0-9-_,+=]+)$ _core/frontend.php?route=$1 [QSA,L] RewriteRule ^([a-z0-9-_,+=]+)\/$ _core/frontend.php?route=$1 [QSA,L] RewriteRule ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)$ _core/frontend.php?route=$1/$2 [QSA,L] RewriteRule ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)\/$ _core/frontend.php?route=$1/$2 [QSA,L] RewriteRule ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)$ _core/frontend.php?route=$1/$2/$3 [QSA,L] RewriteRule ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)\/$ _core/frontend.php?route=$1/$2/$3 [QSA,L] I have come up with the following server configuration for the site, but I am met with unmatched rules after parsing a request (eg; GET /user/auth): attempted nginx rewrite location / { # File handler rewrite ^([a-z0-9-_,+=]+)\.([a-z]+)?(.*)$ /_core/frontend.php?type=$2&file=$1&$3 break; # Page handler rewrite ^([a-z0-9-_,+=]+)(\/*)?(.*)$ /_core/frontend.php?route=$1&$2 break; rewrite ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)(\/*)?(.*)$ /_core/frontend.php?route=$1/$2&$3 break; rewrite ^([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)\/([a-z0-9-_,+=]+)(\/*)?(.*)$ /_core/frontend.php?route=$1/$2/$3&$4 break; } What would you suggest for dealing with my File Handler (which is just filename.ext), and my Page Handler (which is a unique route request with up to 3 properties defined by a forward slash)? As I haven't gotten a response from this yet, I am also unsure if this will override my PHP parser which is defined with location ~ \.php {}, which is included before these rewrite rules. Bonus points if I can solve the parsing issues without the need to use a new rule for each number of route properties.

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  • Running Mathimatica-5 remotely

    - by oxinabox.ucc.asn.au
    Ok, I have Mathmatica 5 - a powerful CAS. I have a cheap netbook, wich not olny is too slow to run mathmatica on, I doubt it has the harddrive space. I do however have remote access to a number of very powerful computers, (most of wich run variose linuxes, but one of which is windows server 2008) Mostly over SSH but other protocols can be arraged for some, i'm sure. (I might even be able to remote desktop the windows server 2008) So I'ld like to install Mathmatica onto one of these machine and then run it remotely. Either from the command line via putty or via some other method. I glanced through the mathmatical documentaion and read soemthing about using some MathLink program, wich linkes the front end istalled on my computer to a remote kernal. Anyone have any expirience with this? I'm not sure if this belongs here or in SuperUser.

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  • What is the simplest way to interpolate and lookup in an x,y table in excel?

    - by dassouki
    I would like to do a lookup and interpolation based on x, y data for the following table. I'd like the equation to be as simple as possible to reduce the amount of possible errors. The full table is about 50 rows x 30 columns. I have about 20 of those tables. Here is an extract from one: A B C D 1 0.1 0.2 0.3 2 2.4 450 300 50 3 2.3 500 375 52 4 2.1 550 475 55 5 1.8 600 600 60 For example, the equation should find the value for x = 2.27 and y = 0.15

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  • Less daunting front end for SQL Server

    - by Martin
    We currently have a few users who have been using Access very succesfully to throw around large amounts of data. We've now got to the point where the data is just too large to be held in Access, as well as wanting to hold it in a single place where multiple users can access it. We have therefore moved the data over to SQL Server. I want to provide a general tool that they can use to view the data on the server and do some simple things like run queries and filters and export the data for offline manipulation. I don't want the support headaches that might come with rolling out SQL Management Studio, and neither do I want to have to create an Access database with links for each current database or ones that are created in the future. Can anyone recommend a simple tool that will connect to a server, list all the databases and allow a user to drill into a table and look at the data. Many thanks.

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  • Sample uniformly at random from an n-dimensional unit simplex.

    - by dreeves
    Sampling uniformly at random from an n-dimensional unit simplex is the fancy way to say that you want n random numbers such that they are all non-negative, they sum to one, and every possible vector of n non-negative numbers that sum to one are equally likely. In the n=2 case you want to sample uniformly from the segment of the line x+y=1 (ie, y=1-x) that is in the positive quadrant. In the n=3 case you're sampling from the triangle-shaped part of the plane x+y+z=1 that is in the positive octant of R3: (Image from http://en.wikipedia.org/wiki/Simplex.) Note that picking n uniform random numbers and then normalizing them so they sum to one does not work. You end up with a bias towards less extreme numbers. Similarly, picking n-1 uniform random numbers and then taking the nth to be one minus the sum of them also introduces bias. Wikipedia gives two algorithms to do this correctly: http://en.wikipedia.org/wiki/Simplex#Random_sampling (Though the second one currently claims to only be correct in practice, not in theory. I'm hoping to clean that up or clarify it when I understand this better. I initially stuck in a "WARNING: such-and-such paper claims the following is wrong" on that Wikipedia page and someone else turned it into the "works only in practice" caveat.) Finally, the question: What do you consider the best implementation of simplex sampling in Mathematica (preferably with empirical confirmation that it's correct)? Related questions http://stackoverflow.com/questions/2171074/generating-a-probability-distribution http://stackoverflow.com/questions/3007975/java-random-percentages

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  • Curve fitting: Find the smoothest function that satisfies a list of constraints.

    - by dreeves
    Consider the set of non-decreasing surjective (onto) functions from (-inf,inf) to [0,1]. (Typical CDFs satisfy this property.) In other words, for any real number x, 0 <= f(x) <= 1. The logistic function is perhaps the most well-known example. We are now given some constraints in the form of a list of x-values and for each x-value, a pair of y-values that the function must lie between. We can represent that as a list of {x,ymin,ymax} triples such as constraints = {{0, 0, 0}, {1, 0.00311936, 0.00416369}, {2, 0.0847077, 0.109064}, {3, 0.272142, 0.354692}, {4, 0.53198, 0.646113}, {5, 0.623413, 0.743102}, {6, 0.744714, 0.905966}} Graphically that looks like this: We now seek a curve that respects those constraints. For example: Let's first try a simple interpolation through the midpoints of the constraints: mids = ({#1, Mean[{#2,#3}]}&) @@@ constraints f = Interpolation[mids, InterpolationOrder->0] Plotted, f looks like this: That function is not surjective. Also, we'd like it to be smoother. We can increase the interpolation order but now it violates the constraint that its range is [0,1]: The goal, then, is to find the smoothest function that satisfies the constraints: Non-decreasing. Tends to 0 as x approaches negative infinity and tends to 1 as x approaches infinity. Passes through a given list of y-error-bars. The first example I plotted above seems to be a good candidate but I did that with Mathematica's FindFit function assuming a lognormal CDF. That works well in this specific example but in general there need not be a lognormal CDF that satisfies the constraints.

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