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  • Object of an abstract class

    - by webgenius
    Why is it not possible to create an object of an abstract class? I understand that the compiler creates a VTABLE with VPTR pointing to NULL. Does this prevent from creating an object of an abstract class?

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  • Set a default value to a property

    - by BrunoLM
    Is it possible to set a default value without the body of a property? Maybe through annotations? [SetTheDefaultValueTo(true)] public bool IsTrue { get; set; } [SetTheDefaultValueTo(false)] public bool IsFalse { get; set; } public void Something() { var isTrue = this.IsTrue; var isFalse = this.IsFalse; }

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  • Numpy zero rank array indexing/broadcasting

    - by Lemming
    I'm trying to write a function that supports broadcasting and is fast at the same time. However, numpy's zero-rank arrays are causing trouble as usual. I couldn't find anything useful on google, or by searching here. So, I'm asking you. How should I implement broadcasting efficiently and handle zero-rank arrays at the same time? This whole post became larger than anticipated, sorry. Details: To clarify what I'm talking about I'll give a simple example: Say I want to implement a Heaviside step-function. I.e. a function that acts on the real axis, which is 0 on the negative side, 1 on the positive side, and from case to case either 0, 0.5, or 1 at the point 0. Implementation Masking The most efficient way I found so far is the following. It uses boolean arrays as masks to assign the correct values to the corresponding slots in the output vector. from numpy import * def step_mask(x, limit=+1): """Heaviside step-function. y = 0 if x < 0 y = 1 if x > 0 See below for x == 0. Arguments: x Evaluate the function at these points. limit Which limit at x == 0? limit > 0: y = 1 limit == 0: y = 0.5 limit < 0: y = 0 Return: The values corresponding to x. """ b = broadcast(x, limit) out = zeros(b.shape) out[x>0] = 1 mask = (limit > 0) & (x == 0) out[mask] = 1 mask = (limit == 0) & (x == 0) out[mask] = 0.5 mask = (limit < 0) & (x == 0) out[mask] = 0 return out List Comprehension The following-the-numpy-docs way is to use a list comprehension on the flat iterator of the broadcast object. However, list comprehensions become absolutely unreadable for such complicated functions. def step_comprehension(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) out.flat = [ ( 1 if x_ > 0 else ( 0 if x_ < 0 else ( 1 if l_ > 0 else ( 0.5 if l_ ==0 else ( 0 ))))) for x_, l_ in b ] return out For Loop And finally, the most naive way is a for loop. It's probably the most readable option. However, Python for-loops are anything but fast. And hence, a really bad idea in numerics. def step_for(x, limit=+1): b = broadcast(x, limit) out = empty(b.shape) for i, (x_, l_) in enumerate(b): if x_ > 0: out[i] = 1 elif x_ < 0: out[i] = 0 elif l_ > 0: out[i] = 1 elif l_ < 0: out[i] = 0 else: out[i] = 0.5 return out Test First of all a brief test to see if the output is correct. >>> x = array([-1, -0.1, 0, 0.1, 1]) >>> step_mask(x, +1) array([ 0., 0., 1., 1., 1.]) >>> step_mask(x, 0) array([ 0. , 0. , 0.5, 1. , 1. ]) >>> step_mask(x, -1) array([ 0., 0., 0., 1., 1.]) It is correct, and the other two functions give the same output. Performance How about efficiency? These are the timings: In [45]: xl = linspace(-2, 2, 500001) In [46]: %timeit step_mask(xl) 10 loops, best of 3: 19.5 ms per loop In [47]: %timeit step_comprehension(xl) 1 loops, best of 3: 1.17 s per loop In [48]: %timeit step_for(xl) 1 loops, best of 3: 1.15 s per loop The masked version performs best as expected. However, I'm surprised that the comprehension is on the same level as the for loop. Zero Rank Arrays But, 0-rank arrays pose a problem. Sometimes you want to use a function scalar input. And preferably not have to worry about wrapping all scalars in at least 1-D arrays. >>> step_mask(1) Traceback (most recent call last): File "<ipython-input-50-91c06aa4487b>", line 1, in <module> step_mask(1) File "script.py", line 22, in step_mask out[x>0] = 1 IndexError: 0-d arrays can't be indexed. >>> step_for(1) Traceback (most recent call last): File "<ipython-input-51-4e0de4fcb197>", line 1, in <module> step_for(1) File "script.py", line 55, in step_for out[i] = 1 IndexError: 0-d arrays can't be indexed. >>> step_comprehension(1) array(1.0) Only the list comprehension can handle 0-rank arrays. The other two versions would need special case handling for 0-rank arrays. Numpy gets a bit messy when you want to use the same code for arrays and scalars. However, I really like to have functions that work on as arbitrary input as possible. Who knows which parameters I'll want to iterate over at some point. Question: What is the best way to implement a function as the one above? Is there a way to avoid if scalar then like special cases? I'm not looking for a built-in Heaviside. It's just a simplified example. In my code the above pattern appears in many places to make parameter iteration as simple as possible without littering the client code with for loops or comprehensions. Furthermore, I'm aware of Cython, or weave & Co., or implementation directly in C. However, the performance of the masked version above is sufficient for the moment. And for the moment I would like to keep things as simple as possible.

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  • What did you develop using a microcontroller?

    - by DR
    I've always been fascinated by microcontrollers and I'm planning to do a few hobby projects just to satisfy my inner geek :) I'm looking for ideas and motivation, so what did you develop using a microcontroller? If possible please state the microcontroller and/or development environment and an estimate on hardware costs beyond the basic equipment (if applicable). I'm interested in both successful and failed projects and any problems you encountered.

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  • Junit run not picking file src/test/resources. For file required by some dependency jar

    - by saddy-dj
    Hi, I m facing a issue where test/resource is not picked,but instead jar's main/resource is picked Scenario is like : Myproject src/test/resources--- have config.xml w which should be needed by abc.jar which is a dependecy in Myproject. When running test case for Myproject its loading config.xml of abc.jar instead of Myproject test/resources. - I need to know order in which maven pick resources. - Or wat im trying is not possible. Thanks.

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  • How to add information to about screen of my cocoa app in Mac Os X

    - by Unicorn
    Hi All, I am pretty new in developing cocoa applications. I have developed a small UI application using cocoa. I wanted to add some information on about screen, currently it shows the app name and version which is 1.00. Can any one help me how i can add some information in about screen, is it possible to add information programmatically instead of hard coding it ? Any help will be appreciated.

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  • Multiple child in virtuemart

    - by handoyo
    Hi all,i want to ask. I'm intending to make custom build computer page with virtuemart. As example,customer can choose the processor,mainboard,optical drive,etc then sum the prices and display it.Is it possible to do it? How to do it? Thanks..

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  • Focus next textview automatically

    - by Naseer
    I have a TextView with android:maxLength set to 3 and another with android:maxLength set to 7. I want focus to automatically move to the second TextView once the 3 chars of the first TextView are filled up. Is this possible without inheriting TextView and writing a custom implementation ?

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  • Managing several custom content types from one module(drupal)

    - by Andrew
    Is it possible to declare and manage several custom content types inside one module? I'm creating a site that needs four custom content types and I'd like to manage them from one module instead of creating module for every content type. After some testing, I found out that it seems impossible. Because, unless hook_form and content type share the same name of module, drupal doesn't call hook_form. Here's how I'd like to do - function mycontent_node_info(){ return array( 'mycontent1' => array( 'name' => t('....'), 'module' => 'mycontent', 'description' => t('...), 'has_title' => TRUE, 'title_label' => t('Title'), 'has_body' => TRUE, 'body_label' => t('content body'), ), 'mycontent2' => array( ....... ), 'mycontent3' => array( ...... ), 'mycontent4' => array( ...... ), ); } function mycontent1_form(&$node){ $form['control1'] = array( '#type' => 'select', '#options' => array( '0' => t('selection 1'), '1' => t('selection 2'), ), '#attributes' => array('id'=>'control1'), ); $form['control2'] = array( '#type' => 'select', '#options' => array( '0' => t('1'), '1' => t('2'), '2' => t('3'), '3' => t('4'), ), '#attributes' => array('id'=>'control2'), ); return $form; } function mycontent2_form(&$node){ .... } function mycontent3_form(&$node){ .... } function mycontent4_form(&$node){ .... } Am I doing something wrong here or is not possible and there's no alternative other than creating module for every content types. I appreciate much your help.

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  • JQuery.ajax(): Problem with parameter data when consuming a WCF Service

    - by Torben H.
    Hello, I'm using JQuery to consume a WCF Service. Actually this works fine: var para = ' { "Parameter" : { "ID" : "5", "Name" : "Peter" } }' $.ajax({ type: "POST", contentType: "application/json", data: para, url: url success: success }); But I don't want to pass the data parameter as String and I think it should be possible to pass ist as array in any way. Like that: var para = { "Parameter" : { "ID" : 5, "Name" : "Peter" } } But when I try this I'm getting an error. What I'm doing wrong? Thanks

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  • Free java or flash file browser for photogallery

    - by Christian
    Hi. I'm about to develop a small web gallery, where it's supposed to be possible to upload several pictures at a time and then add some info abut the pictures.So I need a free java or flash local file browser that can pass me some info of the pictures that gets uploaded so that I can create some SQL entries for each picture. The platform for the project will be PHP and MySQL. Any good recommendations?

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  • How can I run ARM code from external memory?

    - by samoz
    I am using an LPC2132 ARM chip to develop a program. However, my program has grown larger than the space on the chip. How can I connect my chip to some sort of external memory chip to hold additional executable code? Is this possible? If not, what do people normally do when they run out of chip space?

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  • C99 mixed declarations and code in open source projects?

    - by Eduardo
    Why is still C99 mixed declarations and code not used in open source C projects like the Linux kernel or GNOME? I really like mixed declarations and code since it makes the code more readable and prevents hard to see bugs by restricting the scope of the variables to the narrowest possible. This is recommended by Google for C++. For example, Linux requires at least GCC 3.2 and GCC 3.1 has support for C99 mixed declarations and code

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  • How do I create and read non-global variables that aren't destroyed at end of function?

    - by Paul Reilly
    I am attempting to code some plugins to use with MIDI sequencers but have hit a stumbling block. I can't use global-scope variables to store information because multiple instances of the .dll can exist which share memory. How do I create a class (for re-usability purposes in other plugins) containing 2 dimensional array and other variables the content of which is to be shared between functions? If that is possible, how would I read and write the data from the function in the framework where I do the processing?

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  • How to build a tree from a list of items and their children recursively in php?

    - by k1lljoy
    I have a list of items stored in the DB, simplified schema is like this: id, parent, name I need to generate a tree structure (in a form of a multi-dimensional array) that can be infinite levels deep. Top level items would have parent = 0. Next level down would have parent equal to the the id of the parent item, fairly straight forward. What would be the best way to do this, while consuming as little resources as possible?

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