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• Object-Oriented equivalent of LISP's progn function?

  - by Archer

  I'm currently writing a LISP parser that iterates through some AutoLISP code and does its best to make it a little easier to read (changing prefix notation to infix notation, changing setq assignments to "=" assignments, etc.) for those that aren't used to LISP code/only learned object oriented programming. While writing commands that LISP uses to add to a "library" of LISP commands, I came across the LISP command "progn". The only problem is that it looks like progn is simply executing code in a specific order and sometimes (not usually) assigning the last value to a variable. Am I incorrect in assuming that for translating progn to object-oriented understanding that I can simply forgo the progn function and print the statements that it contains? If not, what would be a good equivalent for progn in an object-oriented language?

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• Domain Models (PHP)

  - by Calum Bulmer

  I have been programming in PHP for several years and have, in the past, adopted methods of my own to handle data within my applications. I have built my own MVC, in the past, and have a reasonable understanding of OOP within php but I know my implementation needs some serious work. In the past I have used an is-a relationship between a model and a database table. I now know after doing some research that this is not really the best way forward. As far as I understand it I should create models that don't really care about the underlying database (or whatever storage mechanism is to be used) but only care about their actions and their data. From this I have established that I can create models of lets say for example a Person an this person object could have some Children (human children) that are also Person objects held in an array (with addPerson and removePerson methods, accepting a Person object). I could then create a PersonMapper that I could use to get a Person with a specific 'id', or to save a Person. This could then lookup the relationship data in a lookup table and create the associated child objects for the Person that has been requested (if there are any) and likewise save the data in the lookup table on the save command. This is now pushing the limits to my knowledge..... What if I wanted to model a building with different levels and different rooms within those levels? What if I wanted to place some items in those rooms? Would I create a class for building, level, room and item with the following structure. building can have 1 or many level objects held in an array level can have 1 or many room objects held in an array room can have 1 or many item objects held in an array and mappers for each class with higher level mappers using the child mappers to populate the arrays (either on request of the top level object or lazy load on request) This seems to tightly couple the different objects albeit in one direction (ie. a floor does not need to be in a building but a building can have levels) Is this the correct way to go about things? Within the view I am wanting to show a building with an option to select a level and then show the level with an option to select a room etc.. but I may also want to show a tree like structure of items in the building and what level and room they are in. I hope this makes sense. I am just struggling with the concept of nesting objects within each other when the general concept of oop seems to be to separate things. If someone can help it would be really useful. Many thanks

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• Good Literature for "Object oriented programming in C"

  - by Dipan Mehta

  This is not a debate question about whether or not C is a good candidate for Object oriented programming or not. Quite often C is the primary platform where the development is happening. I have seen, and hopefully learnt through crawling many open source and commercial projects - that while the language inherently doesn't stop you if you create "non-object" code. However, you can still think in the "Object" way and reasonably write code that captures this designs thinking. For those who has done this, OO way is still the best way to write code even when you are programming in C. While, I have learnt most of it through the hard way, are there any deep literature that can help educate the relatively young guys about how to do OO programming in C?

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• Objected oriented approach to structure inside structure

  - by RishiD

  This is for C++ but should apply to any OO language. Trying to figure out the correct object oriented apporach to do the following (this is what I do in C). struct Container { enum type; union { TypeA a; TypeB b; }; } The type field determines if it TypeA or TypeB object. I am using this to handle responses coming back from a connection, they get parsed and get put into this structure and then based on the message type the appropriate fields get filled in. e.g. struct Container parseResponse(bufferIn, bufferLength); Is there an OO approach for doing this?

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• What is a good design model for my new class?

  - by user66662

  I am a beginning programmer who, after trying to manage over 2000 lines of procedural php code, now has discovered the value of OOP. I have read a few books to get me up to speed on the beginning theory, but would like some advice on practical application. So,for example, let's say there are two types of content objects - an ad and a calendar event. what my application does is scan different websites (a predefined list), and, when it finds an ad or an event, it extracts the data and saves it to a database. All of my objects will share a $title and $description. However, the Ad object will have a $price and the Event object will have $startDate. Should I have two separate classes, one for each object? Should I have a 'superclass' with the $title and $description with two other Ad and Event classes with their own properties? The latter is at least the direction I am on now. My second question about this design is how to handle the logic that extracts the data for $title, $description, $price, and $date. For each website in my predefined list, there is a specific regex that returns the desired value for each property. Currently, I have an extremely large switch statement in my constructor which determines what website I am own, sets the regex variables accordingly, and continues on. Not only that, but now I have to repeat the logic to determine what site I am on in the constructor of each class. This doesn't feel right. Should I create another class Algorithms and store the logic there for each site? Should the functions of to handle that logic be in this class? or specific to the classes whos properties they set? I want to take into account in my design two things: 1) I will add different content objects in the future that share $title and $description, but will have their own properties, so, I want to be able to easily grow these as needed. 2) I will add more websites constantly (each with their own algorithms for data extraction) so I would like to plan efficienty managing and working with these now. I thought about extending the Ad or Event class with 'websiteX' class and store its functions there. But, this didn't feel right either as now I have to manage 100s of little website specific class files. Note, I didn't know if this was the correct site or stackoverflow was the better choice. If so, let me know and I'll post there.

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• Is the "impossible object" possible in computer graphics?

  - by CPP_Person

  This may be a silly question but I want to know the answer to it. I saw this thing called the "impossible object", while they're many different images of this online, it's suppost to be impossible geometry. Here is an example: Now as far as logic goes, I know you don't have to obey it in games, such as a flying cow, or an impossible object. So that's out of the way, but what stands in my way is whether or not there is a way to draw this onto a 3D scene. Like is there a way to represent it as a 3D object? Thanks!

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• Which technology is best suited to store and query a huge readonly graph?

  - by asmaier

  I have a huge directed graph: It consists of 1.6 million nodes and 30 million edges. I want the users to be able to find all the shortest connections (including incoming and outgoing edges) between two nodes of the graph (via a web interface). At the moment I have stored the graph in a PostgreSQL database. But that solution is not very efficient and elegant, I basically need to store all the edges of the graph twice (see my question PostgreSQL: How to optimize my database for storing and querying a huge graph). It was suggested to me to use a GraphDB like neo4j or AllegroGraph. However the free version of AllegroGraph is limited to 50 million nodes and also has a very high-level API (RDF), which seems too powerful and complex for my problem. Neo4j on the other hand has only a very low level API (and the python interface is not mature yet). Both of them seem to be more suited for problems, where nodes and edges are frequently added or removed to a graph. For a simple search on a graph, these GraphDBs seem to be too complex. One idea I had would be to "misuse" a search engine like Lucene for the job, since I'm basically only searching connections in a graph. Another idea would be, to have a server process, storing the whole graph (500MB to 1GB) in memory. The clients could then query the server process and could transverse the graph very quickly, since the graph is stored in memory. Is there an easy possibility to write such a server (preferably in Python) using some existing framework? Which technology would you use to store and query such a huge readonly graph?

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• Add a wall post to a page or application wall as page or application with facebook graph API

  - by blauesocke

  Hi, I wan't to create a new wall post on a appliaction page or a "normal" page with the facebook graph API. Is there a way to "post as page"? With the old REST-API it worked like this: $facebook->api_client->stream_publish($message, NULL, $links, $targetPageId, $asPageId); So, if I passed equal IDs for $targetPageId and $asPageId I was able to post a "real" wall post not caused by my own facebook account. Thanks!

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• How can I get node coordinates from a graph, using Perl?

  - by jonny

  Ok, I have a flowchart definition (basically, array of nodes and edges for each node). Now I want to calculate coordinates for every task in the flow, preferably hierarchycal style. I need something like Graph::Easy::Layout but I have no idea how to get nodes coordinates: I render nodes myself and I only want to retrieve box coordinates/size. Any suggestions? What I need is a CPAN module available even in Debian repository.

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• Javascript object list sorting by object property

  - by Constructor

  I need to do this: (sorry not in javascript syntax-still learning object language :) ) object=car attibutes:top-speed, brand.... now I want to sort the list of those cars in order by top-speed, brand... How do I do this (please note the solution must be javascript only, no php or other stuff) ?

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• Nhibernate/Hibernate, lookup tables and object design

  - by Simon G

  Hi, I've got two tables. Invoice with columns CustomerID, InvoiceDate, Value, InvoiceTypeID (CustomerID and InvoiceDate make up a composite key) and InvoiceType with InvoiceTypeID and InvoiceTypeName columns. I know I can create my objects like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceType InvoiceType { get; set; } } public class InvoiceType { public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } So the generated sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice WHERE CustomerID = x AND InvoiceDate = y SELECT InvoiceTypeID, InvoiceTypeName FROM InvoiceType WHERE InvoiceTypeID = z But rather that having two select queries executed to retrieve the data I would rather have one. I would also like to avoid using child object for simple lookup lists. So my object would look something like: public class Invoice { public virtual int CustomerID { get; set; } public virtual DateTime InvoiceDate { get; set; } public virtual decimal Value { get; set; } public virtual InvoiceTypeID { get; set; } public virtual InvoiceTypeName { get; set; } } And my sql would look something like: SELECT CustomerID, InvoiceDate, Value, InvoiceTypeID FROM Invoice INNER JOIN InvoiceType ON Invoice.InvoiceTypeID = InvoiceType.InvoiceTypeID WHERE CustomerID = x AND InvoiceDate = y My question is how do I create the mapping for this? I've tried using join but this tried to join using CustomerID and InvoiceDate, am I missing something obvious? Thanks

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• Getting my head around object oriented programing

  - by nLL

  I am entry level .Net developer and using it to develop web sites. I started with classic asp and last year jumped on the ship with a short C# book. As I developed I learned more and started to see that coming from classic asp I always used C# like scripting language. For example in my last project I needed to encode video on the webserver and wrote a code like public class Encoder { Public static bool Encode(string videopath) { ...snip... return true; } } While searching samples related to my project I’ve seen people doing this public class Encoder { Public static Encode(string videopath) { EncodedVideo encoded = new EncodedVideo(); ...snip... encoded.EncodedVideoPath = outputFile; encoded.Success = true; ...snip... } } public class EncodedVideo { public string EncodedVideoPath { get; set; } public bool Success { get; set; } } As I understand second example is more object oriented but I don’t see the point of using EncodedVideo object. Am I doing something wrong? Does it really necessary to use this sort of code in a web app?

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• Designing a class in such a way that it doesn't become a "God object"

  - by devoured elysium

  I'm designing an application that will allow me to draw some functions on a graphic. Each function will be drawn from a set of points that I will pass to this graphic class. There are different kinds of points, all inheriting from a MyPoint class. For some kind of points it will be just printing them on the screen as they are, others can be ignored, others added, so there is some kind of logic associated to them that can get complex. How to actually draw the graphic is not the main issue here. What bothers me is how to make the code logic such that this GraphicMaker class doesn't become the so called God-Object. It would be easy to make something like this: class GraphicMaker { ArrayList<Point> points = new ArrayList<Point>(); public void AddPoint(Point point) { points.add(point); } public void DoDrawing() { foreach (Point point in points) { if (point is PointA) { //some logic here else if (point is PointXYZ) { //...etc } } } } How would you do something like this? I have a feeling the correct way would be to put the drawing logic on each Point object (so each child class from Point would know how to draw itself) but two problems arise: There will be kinds of points that need to know all the other points that exist in the GraphicObject class to know how to draw themselves. I can make a lot of the methods/properties from the Graphic class public, so that all the points have a reference to the Graphic class and can make all their logic as they want, but isn't that a big price to pay for not wanting to have a God class?

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• Javascript Object Database

  - by Narven

  Hi, is there any javascript object database?? Something like http://www.db4o.com/ but for javascript? thanks

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• convert event an activity node graph to an event node graph

  - by nunos

  Does anyone know where I can find an implementation of an algorithm to convert an activity node graph to an event node graph? Thanks in advance.

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• Is it better to return NULL or empty values from functions/methods where the return value is not present?

  - by P B

  I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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• How can I tag a user in a photo using the Facebook Graph API?

  - by fr6

  I tried: $args = array( 'access_token' => $access_token, 'id' => $uid ); $url = "https://graph.facebook.com/{$idPhoto}/tags"; $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_HEADER, false); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_POSTFIELDS, $args); curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2); $data = curl_exec($ch); It has returned me: {"error":{"type":"QueryParseException","message":"Unknown path components: \/tags"}} It does not seem possible because its not in the Facebook documentation: http://developers.facebook.com/docs/api#publishing Can someone confirm me that it's not possible to tag a user in a recently uploaded photo?

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• How to build Object Oriented Skills?

  - by cedar715

  Being a core developer for couple of years, coding applications seeing the class diagrams, sequence diagrams, I decided to improve my self, taking the next step of designing. As I'm an OO developer, I'm interested in improving my design skills. For Example, I had a hard time designing a currency converter. My questions to the SO: Is it by experience the design skills can be acquired? Will learning books/blog/material over internet etc help? Is it that one needs the domain knowledge of the application being developed? Knowing Design patterns, principles? Studying 'Code Complete' book ? Need to have Problem-solving skills? In short, given a problem, I just want to solve it in Object-oriented way??

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• Error with python-setuptools doing "sudo easy_install python-graph-core"

  - by Dan

  Using easy_install, part of the python-setuptools, I get the following error: $ sudo easy_install python-graph-core [sudo] password for dan: Searching for python-graph-core Reading http://pypi.python.org/simple/python-graph-core/ Reading http://code.google.com/p/python-graph/ Reading http://code.google.com/p/python-graph/downloads/list?can=1 Reading http://code.google.com/p/python-graph/downloads/list Best match: python-graph-core 1.7.0 Downloading http://python-graph.googlecode.com/files/python-graph-core-1.7.0.tar.gz Processing python-graph-core-1.7.0.tar.gz Running python-graph-core-1.7.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-GwpYiM/python-graph-core-1.7.0/egg-dist-tmp-1yqbyV setup.py:8: Warning: 'as' will become a reserved keyword in Python 2.6 Traceback (most recent call last): File "/usr/bin/easy_install", line 8, in <module> load_entry_point('setuptools==0.6c9', 'console_scripts', 'easy_install')() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1671, in main with_ei_usage(lambda: File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1659, in with_ei_usage return f() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 1675, in <lambda> distclass=DistributionWithoutHelpCommands, **kw File "/usr/lib/python2.5/distutils/core.py", line 151, in setup dist.run_commands() File "/usr/lib/python2.5/distutils/dist.py", line 974, in run_commands self.run_command(cmd) File "/usr/lib/python2.5/distutils/dist.py", line 994, in run_command cmd_obj.run() File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 211, in run self.easy_install(spec, not self.no_deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 446, in easy_install return self.install_item(spec, dist.location, tmpdir, deps) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 476, in install_item dists = self.install_eggs(spec, download, tmpdir) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 655, in install_eggs return self.build_and_install(setup_script, setup_base) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 930, in build_and_install self.run_setup(setup_script, setup_base, args) File "/usr/lib/python2.5/site-packages/setuptools/command/easy_install.py", line 919, in run_setup run_setup(setup_script, args) File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 27, in run_setup lambda: execfile( File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 63, in run return func() File "/usr/lib/python2.5/site-packages/setuptools/sandbox.py", line 29, in <lambda> {'__file__':setup_script, '__name__':'__main__'} File "setup.py", line 8 except ImportError as ie: ^ SyntaxError: invalid syntax Any suggestions to what I may be doing wrong? Thanks, Dan

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• Does this copy the reference or the object?

  - by Water Cooler v2

  Sorry, I am being both thick and lazy, but mostly lazy. Actually, not even that. I am trying to save time so I can do more in less time as there's a lot to be done. Does this copy the reference or the actual object data? public class Foo { private NameValueCollection _nvc = null; public Foo( NameValueCollection nvc) { _nvc = nvc; } } public class Bar { public static void Main() { NameValueCollection toPass = new NameValueCollection(); new Foo( toPass ); // I believe this only copies the reference // so if I ever wanted to compare toPass and // Foo._nvc (assuming I got hold of the private // field using reflection), I would only have to // compare the references and wouldn't have to compare // each string (deep copy compare), right? } I think I know the answer for sure: it only copies the reference. But I am not even sure why I am asking this. I guess my only concern is, if, after instantiating Foo by calling its parameterized ctor with toPass, if I needed to make sure that the NVC I passed as toPass and the NVC private field _nvc had the exact same content, I would just need to compare their references, right?

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• Looking for app to work fluidly with CSV data in graph form

  - by Aszurom

  It often occurs to me that if I had a good tool for viewing CSV data in graphical format, and comparing two sets of numbers to each other, I could do a great deal of meaningful trend watching and data interpretation. For example, perfmon can output quite a lot of data about a server into a CSV file, but there's no good way to view it. A lot of scripts could/have been written that would populate CSV files. I could write these all day long. My problem is that I need a great viewer. I've seen quite a few things that will take a CSV file and after a lot of tweaking and user adjustment produce a static gif/png image. A static image doesn't do me a lot of good, because I have to look at it, then re-calibrate the parameters of the program, regenerate the image, repeat. That sucks. I could do this in Excel. Ideally, I would want a FLUID graph viewer. On the fly, I can adjust how much of my timeline I'm viewing. I could adjust the scaling so that one big spike doesn't make 99.9% of the data an unreadable line across the bottom of the X axis. Stuff like that. I should be able to say "show me CSV column 3 and column 5 as graphs. Show me the data scaled for 20 or 150 entries, and let me slide that window up and down the column of data. Auto scale to fit 95% of data within the Y axis and let crazy spikes go off the screen." Maybe I'm terribly spoiled by how you can drag, zoom, and slide data around on my iPad. I want to be able to view a spreadsheet of data with that fluidity and not have to guess at what sort of static snapshot I want to create from it. I don't want to have to make a study of how to tweak some data plotting program to let me import my file and do what I could just do in Excel. I want to scale, zoom, and transform my graph on the fly and then export a snapshot of it once I have it the way I want it. Is there anything out there that fills this need? I'll take linux, osx, win32 or even iOS suggestions.

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• How to find whole graph coverage path in dynamic state-flow diagram?

  - by joseph

  Hello, As I've been researching algorithms for path finding in graph, I found interesting problem. Definition of situation: 1)State diagram can have p states, and s Boolean Fields, and z Int Fields 2)Every state can have q ingoing and r outgoing transitions, and h Int fields (h belongs to z - see above) 3)Every transition can have only 1 event, and only 1 action 4)every action can change n Boolean Fields, and x Int Fields 5)every event can have one trigger from combination of any count of Boolean Fields in diagram 6)Transition can be in OPEN/CLOSED form. If the transition is open/closed depends on trigger2 compounded from 0..c Boolean fields. 7) I KNOW algorithm for finding shortest paths from state A to state B. 8) I KNOW algorithm for finding path that covers all states and transitions of whole state diagram, if all transitions are OPEN. Now, what is the goal: I need to find shortest path that covers all states and transitions in dynamically changing state diagram described above. When an action changes some int field, the algorithm should go through all states that have changed int field. The algorithm should also be able to open and close transition (by going through transitions that open and close another transitions by action) in the way that the founded path will be shortest and covers all transitions and states. Any idea how to solve it? I will be really pleased for ANY idea. Thanks for answers.

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• controlling an object through another object ?

  - by Stefano Borini

  Today I've seen the following pattern: you have an object A and an object B. Object B accepts a pointer to A at its constructor. Once B is created, there's a method B.doCalc() that performs a calculation (internally using A's information). The result is obtained with method B.getResult(). In order to perform another calculation, A is modified, and B.doCalc() is called again. What is your opinion on this choice ? I would have designed it differently, but I want to hear your voice. Edit : note that my main objection is to modify A to have a different result from B, without touching B. Although similar, I think that just this discipline expresses a much better feeling of what's going on. Instead of a = new A a.whatever = 5 b = new B(a) b.doCalc() res = b.getResult() a.whatever = 6 b.doCalc() res = b.getResult() You get the a pointer object from b itself. a = new A a.whatever = 5 b = new B(a) b.doCalc() res = b.getResult() a = b.getAPointer() a.whatever = 6 b.doCalc() res = b.getResult() because it makes more explicit the fact that a is taken from b and then modified. I still don't like it, though...

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• boost graph adjacency_list, retrieving a node's parents

  - by Juan

  I want to find in an adjacency graph from the bgl how give a Vertexdescriptor and get the set of nodes that are parents of this given node. i would like to do this in directed graph, it seems you could use a bidirectional graph but i want to be able to restrict it so that there are no cycles.

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• A minimum spanning tree / shortest path in a directed graph

  - by mvid

  Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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