Search Results

Search found 3047 results on 122 pages for 'subset sum'.

Page 91/122 | < Previous Page | 87 88 89 90 91 92 93 94 95 96 97 98  | Next Page >

• summing up excel files in matlab

  - by AP

  Is there a easy good way to sum up various excel files in matlab? what i really want is similar to dos command type file*.xls sumfile.xls I have from 10-100 excel files with similar file name formats excet the date XXXXX_2010_03_03.xls, XXXXX_2010_03_03.xls and so on..... Is there a command to copy the files one after other. All files are of diff length so i cannot know the position of the rows after each file. I would like to have them copied in same sheet of excel. Thanks

  Read the article

• How do I exclude outliers from an aggregate query?

  - by Margaret

  I'm creating a report comparing total time and volume across units. Here a simplification of the query I'm using at the moment: SELECT m.Unit, COUNT(*) AS Count, SUM(m.TimeInMinutes) AS TotalTime FROM main_table m WHERE m.unit <> '' AND m.TimeInMinutes > 0 GROUP BY m.Unit HAVING COUNT(*) > 15 However, I have been told that I need to exclude cases where the row's time is in the highest or lowest 5% to try and get rid of a few wacky outliers. (As in, remove the rows before the aggregates are applied.) How do I do that?

  Read the article

• "...redeclared as different kind of symbol"?

  - by CodeNewb

  #include <stdio.h> #include <math.h> double integrateF(double low, double high) { double low = 0; double high = 20; double delta_x=0; double x, ans; double s = 1/2*exp((-x*x)/2); for(x=low;x<=high;x++) delta_x = x+delta_x; ans = delta_x*s; return ans; } It says that low and high are "redeclared as different type of symbol" and I don't know what that means. Basically, all I'm doing here (READ: trying) is integrating from low (which I set to 0) to high (20) to find the Riemann sum. The for loop looks kinda trippy too...I'm so lost.

  Read the article

• What is most efficient way of setting row to zeros for a sparce scipy matrix?

  - by Alex Reinking

  I'm trying to convert the following MATLAB code to Python and am having trouble finding a solution that works in any reasonable amount of time. M = diag(sum(a)) - a; where = vertcat(in, out); M(where,:) = 0; M(where,where) = 1; Here, a is a sparse matrix and where is a vector (as are in/out). The solution I have using Python is: M = scipy.sparse.diags([degs], [0]) - A where = numpy.hstack((inVs, outVs)).astype(int) M = scipy.sparse.lil_matrix(M) M[where, :] = 0 # This is the slowest line M[where, where] = 1 M = scipy.sparse.csc_matrix(M) But since A is 334863x334863, this takes like three minutes. If anyone has any suggestions on how to make this faster, please contribute them! For comparison, MATLAB does this same step imperceptibly fast. Thanks!

  Read the article

• Oracle Group By Issue

  - by m_oLogin

  Hello community, I am strugling with what seems an easy problem to tackle (at least for me in MySQL / SqlServer!) I'll simplify the problem. Let's say I have the following table: Table VOTE ID ID_IDEA DATE_VOTE with ID_IDEA FK(IDEA.ID) 1 3 10/10/10 2 0 09/09/10 3 3 08/08/10 4 3 11/11/10 5 0 06/06/10 6 1 05/05/10 I'm trying to find the latest votes given for each individual idea, meaning I want to return only rows with ID 4, 2 and 6. It seems with Oracle that you can't use GROUP BY without using a function like SUM(), AVG, etc. I'm a bit confused about how it's supposed to work. Please advise, Thanks.

  Read the article

• Defining Discovery: Core Concepts

  - by Joe Lamantia

  Discovery tools have had a referencable working definition since at least 2001, when Ben Shneiderman published 'Inventing Discovery Tools: Combining Information Visualization with Data Mining'.  Dr. Shneiderman suggested the combination of the two distinct fields of data mining and information visualization could manifest as new category of tools for discovery, an understanding that remains essentially unaltered over ten years later.  An industry analyst report titled Visual Discovery Tools: Market Segmentation and Product Positioning from March of this year, for example, reads, "Visual discovery tools are designed for visual data exploration, analysis and lightweight data mining." Tools should follow from the activities people undertake (a foundational tenet of activity centered design), however, and Dr. Shneiderman does not in fact describe or define discovery activity or capability. As I read it, discovery is assumed to be the implied sum of the separate fields of visualization and data mining as they were then understood.  As a working definition that catalyzes a field of product prototyping, it's adequate in the short term.  In the long term, it makes the boundaries of discovery both derived and temporary, and leaves a substantial gap in the landscape of core concepts around discovery, making consensus on the nature of most aspects of discovery difficult or impossible to reach.  I think this definitional gap is a major reason that discovery is still an ambiguous product landscape. To help close that gap, I'm suggesting a few definitions of four core aspects of discovery.  These come out of our sustained research into discovery needs and practices, and have the goal of clarifying the relationship between discvoery and other analytical categories.  They are suggested, but should be internally coherent and consistent.   Discovery activity is: "Purposeful sense making activity that intends to arrive at new insights and understanding through exploration and analysis (and for these we have specific defintions as well) of all types and sources of data." Discovery capability is: "The ability of people and organizations to purposefully realize valuable insights that address the full spectrum of business questions and problems by engaging effectively with all types and sources of data." Discovery tools: "Enhance individual and organizational ability to realize novel insights by augmenting and accelerating human sense making to allow engagement with all types of data at all useful scales." Discovery environments: "Enable organizations to undertake effective discovery efforts for all business purposes and perspectives, in an empirical and cooperative fashion." Note: applicability to a world of Big data is assumed - thus the refs to all scales / types / sources - rather than stated explicitly.  I like that Big Data doesn't have to be written into this core set of definitions, b/c I think it's a transitional label - the new version of Web 2.0 - and goes away over time. References and Resources: Inventing Discovery Tools Visual Discovery Tools: Market Segmentation and Product Positioning Logic versus usage: the case for activity-centered design A Taxonomy of Enterprise Search and Discovery

  Read the article

• July, the 31 Days of SQL Server DMO’s – Day 21 (sys.dm_db_partition_stats)

  - by Tamarick Hill

  The sys.dm_db_partition_stats DMV returns page count and row count information for each table or index within your database. Lets have a quick look at this DMV so we can review some of the results. **NOTE: I am going to create an ‘ObjectName’ column in our result set so that we can more easily identify tables. SELECT object_name(object_id) ObjectName, * FROM sys.dm_db_partition_stats As stated above, the first column in our result set is an Object name based on the object_id column of this result set. The partition_id column refers to the partition_id of the index in question. Each index will have at least 1 unique partition_id and will have more depending on if the object has been partitioned. The index_id column relates back to the sys.indexes table and uniquely identifies an index on a given object. A value of 0 (zero) in this column would indicate the object is a HEAP and a value of 1 (one) would signify the Clustered Index. Next is the partition_number which would signify the number of the partition for a particular object_id. Since none of my tables in my result set have been partitioned, they all display 1 for the partition_number. Next we have the in_row_data_page_count which tells us the number of data pages used to store in-row data for a given index. The in_row_used_page_count is the number of pages used to store and manage the in-row data. If we look at the first row in the result set, we will see we have 700 for this column and 680 for the previous. This means that just to manage the data (not store it) is requiring 20 pages. The next column in_row_reserved_page_count is how many pages have been reserved, regardless if they are being used or not. The next 2 columns are used for storing LOB (Large Object) data which could be text, image, varchar(max), or varbinary(max) columns. The next two columns, row_overflow, represent pages used for data that exceed the 8,060 byte row size limit for the in-row data pages. The next columns used_page_count and reserved_page_count represent the sum of the in_row, lob, and row_overflow columns discussed earlier. Lastly is a row_count column which displays the number of rows that are in a particular index. This DMV is a very powerful resource for identifying page and row count information. By knowing the page counts for indexes within your database, you are able to easily calculate the size of indexes. For more information on this DMV, please see the below Books Online link: http://msdn.microsoft.com/en-us/library/ms187737.aspx Follow me on Twitter @PrimeTimeDBA

  Read the article

• DBCC MEMUSAGE in 2005/8 ?

  - by steveh99999

  I used to like using undocumented command DBCC MEMUSAGE in SQL 2000 to see which tables were using space in SQL data cache. In SQL 2005, this command is not longer present. Instead a DMV – sys.dm_os_buffer_descriptors – can be used to display data cache contents,  but this doesn’t quite give you the same output as DBCC MEMUSAGE. I’m also aware that you can use Quest’s spotlight tool to view a summary of data cache contents. Using  this post by Umachandar Jayachandran  of Microsoft, I was able to create the following equivalent for SQL 2005/8. I’ve wrapped Umachandar’s original query in a CTE to produce summary information :- ;WITH memusage_CTE AS (SELECT bd.database_id, bd.file_id, bd.page_id, bd.page_type , COALESCE(p1.object_id, p2.object_id) AS object_id , COALESCE(p1.index_id, p2.index_id) AS index_id , bd.row_count, bd.free_space_in_bytes, CONVERT(TINYINT,bd.is_modified) AS 'DirtyPage' FROM sys.dm_os_buffer_descriptors AS bd JOIN sys.allocation_units AS au ON au.allocation_unit_id = bd.allocation_unit_id OUTER APPLY ( SELECT TOP(1) p.object_id, p.index_id FROM sys.partitions AS p WHERE p.hobt_id = au.container_id AND au.type IN (1, 3) ) AS p1 OUTER APPLY ( SELECT TOP(1) p.object_id, p.index_id FROM sys.partitions AS p WHERE p.partition_id = au.container_id AND au.type = 2 ) AS p2 WHERE  bd.database_id = DB_ID() AND bd.page_type IN ('DATA_PAGE', 'INDEX_PAGE') ) SELECT TOP 20 DB_NAME(database_id) AS 'Database',OBJECT_NAME(object_id,database_id) AS 'Table Name', index_id,COUNT(*) AS 'Pages in Cache', SUM(dirtyPage) AS 'Dirty Pages' FROM memusage_CTE GROUP BY database_id, object_id, index_id ORDER BY COUNT(*) DESC I’m not 100% happy with the results of the above query however… I’ve noticed that on a busy BizTalk messageBox database  it will return information on pages that contain GHOST rows – . ie where data has already been deleted but has yet to be cleaned-up by a background process – I’m need to investigate further why cache on this server apparently contains so much GHOST data… For more information on the background ghost cleanup process, see this article by Paul Randall. However, I think the results of this query should still be of interest to a DBA. I have another post to come shortly regarding an example I encountered where this information proved useful to me… I notice in SQL 2008, sys.dm_os_buffer_descriptors gained an extra column – numa_mode – I’m interested to see how this is populated and how useful this column can be on a NUMA-enabled system. I’m assuming in theory you could use this column to help analyse how your tables are spread across Numa-enabled data-cache ?

  Read the article

• Delegates in c#

  - by Jalpesh P. Vadgama

  I have used delegates in my programming since C# 2.0. But I have seen there are lots of confusion going on with delegates so I have decided to blog about it. In this blog I will explain about delegate basics and use of delegates in C#. What is delegate? We can say a delegate is a type safe function pointer which holds methods reference in object. As per MSDN it's a type that references to a method. So you can assign more than one methods to delegates with same parameter and same return type. Following is syntax for the delegate public delegate int Calculate(int a, int b); Here you can see the we have defined the delegate with two int parameter and integer parameter as return parameter. Now any method that matches this parameter can be assigned to above delegates. To understand the functionality of delegates let’s take a following simple example. using System; namespace Delegates { class Program { public delegate int CalculateNumber(int a, int b); static void Main(string[] args) { int a = 5; int b = 5; CalculateNumber addNumber = new CalculateNumber(AddNumber); Console.WriteLine(addNumber(5, 6)); Console.ReadLine(); } public static int AddNumber(int a, int b) { return a + b; } } } Here in the above code you can see that I have created a object of CalculateNumber delegate and I have assigned the AddNumber static method to it. Where you can see in ‘AddNumber’ static method will just return a sum of two numbers. After that I am calling method with the help of the delegates and printing out put to the console application. Now let’s run the application and following is the output as expected. That’s it. You can see the out put of delegates after adding a number. This delegates can be used in variety of scenarios. Like in web application we can use it to update one controls properties from another control’s action. Same you can also call a delegates whens some UI interaction done like button clicked. Hope you liked it. Stay tuned for more. In next post I am going to explain about multicast delegates. Till then happy programming.

  Read the article

• Mathemagics - 3 consecutive number

  - by PointsToShare

  © 2011 By: Dov Trietsch. All rights reserved Three Consecutive numbers When I was young and handsome (OK, OK, just young), my father used to challenge us with riddles and tricks involving Logic, Math and general knowledge. Most of the time, at least after reaching the ripe age of 10, I would see thru his tricks in no time. This one is a bit more subtle. I had to think about it for close to an hour and then when I had the ‘AHA!’ effect, I could not understand why it had taken me so long. So here it is. You select a volunteer from the audience (or a shill, but that would be cheating!) and ask him to select three consecutive numbers, all of them 1 or 2 digits. So {1, 2, 3} would be good, albeit trivial set, as would {8, 9, 10} or {97, 98, 99} but not {99, 99, 100} (why?!). Now, using a calculator – and these days almost every phone has a built in calculator – he is to perform these steps: 1.      Select a single digit 2.      Multiply it by 3 and write it down 3.      Add the 3 consecutive numbers 4.      Add the number from step 2 5.      Multiply the sum by 67 6.      Now tell me the last 2 digits of the result and also the number you wrote down in step 2 I will tell you which numbers you selected. How do I do this? I’ll give you the mechanical answer, but because I like you to have the pleasure of an ‘AHA!’ effect, I will not really explain the ‘why’. So let’s you selected 30, 31, and 32 and also that your 3 multiple was 24, so here is what you get 30 + 31 + 32 = 93 93 + 24 = 117 117 x 67 = 7839, last 2 digits are 39, so you say “the last 2 digits are 39, and the other number is 24.” Now, I divide 24 by 3 getting 8. I subtract 8 from 39 and get 31. I then subtract 1 from this getting 30, and say: “You selected 30, 31, and 32.” This is the ‘how’. I leave the ‘why’ to you! That’s all folks! PS do you really want to know why? Post a feedback below. When 11 people or more will have asked for it, I’ll add a link to the full explanation.

  Read the article

• Tuxedo Load Balancing

  - by Todd Little

  A question I often receive is how does Tuxedo perform load balancing.  This is often asked by customers that see an imbalance in the number of requests handled by servers offering a specific service. First of all let me say that Tuxedo really does load or request optimization instead of load balancing.  What I mean by that is that Tuxedo doesn't attempt to ensure that all servers offering a specific service get the same number of requests, but instead attempts to ensure that requests are processed in the least amount of time.   Simple round robin "load balancing" can be employed to ensure that all servers for a particular service are given the same number of requests.  But the question I ask is, "to what benefit"?  Instead Tuxedo scans the queues (which may or may not correspond to servers based upon SSSQ - Single Server Single Queue or MSSQ - Multiple Server Single Queue) to determine on which queue a request should be placed.  The scan is always performed in the same order and during the scan if a queue is empty the request is immediately placed on that queue and request routing is done.  However, should all the queues be busy, meaning that requests are currently being processed, Tuxedo chooses the queue with the least amount of "work" queued to it where work is the sum of all the requests queued weighted by their "load" value as defined in the UBBCONFIG file.  What this means is that under light loads, only the first few queues (servers) process all the requests as an empty queue is often found before reaching the end of the scan.  Thus the first few servers in the queue handle most of the requests.  While this sounds non-optimal, in fact it capitalizes on the underlying operating systems and hardware behavior to produce the best possible performance.  Round Robin scheduling would spread the requests across all the available servers and thus require all of them to be in memory, and likely not share much in the way of hardware or memory caches.  Tuxedo's system maximizes the various caches and thus optimizes overall performance.  Hopefully this makes sense and now explains why you may see a few servers handling most of the requests.  Under heavy load, meaning enough load to keep all servers that can handle a request busy, you should see a relatively equal number of requests processed.  Next post I'll try and cover how this applies to servers in a clustered (MP) environment because the load balancing there is a little more complicated. Regards,Todd LittleOracle Tuxedo Chief Architect

  Read the article

• Unit testing in Django

  - by acjohnson55

  I'm really struggling to write effective unit tests for a large Django project. I have reasonably good test coverage, but I've come to realize that the tests I've been writing are definitely integration/acceptance tests, not unit tests at all, and I have critical portions of my application that are not being tested effectively. I want to fix this ASAP. Here's my problem. My schema is deeply relational, and heavily time-oriented, giving my model object high internal coupling and lots of state. Many of my model methods query based on time intervals, and I've got a lot of auto_now_add going on in timestamped fields. So take a method that looks like this for example: def summary(self, startTime=None, endTime=None): # ... logic to assign a proper start and end time # if none was provided, probably using datetime.now() objects = self.related_model_set.manager_method.filter(...) return sum(object.key_method(startTime, endTime) for object in objects) How does one approach testing something like this? Here's where I am so far. It occurs to me that the unit testing objective should be given some mocked behavior by key_method on its arguments, is summary correctly filtering/aggregating to produce a correct result? Mocking datetime.now() is straightforward enough, but how can I mock out the rest of the behavior? I could use fixtures, but I've heard pros and cons of using fixtures for building my data (poor maintainability being a con that hits home for me). I could also setup my data through the ORM, but that can be limiting, because then I have to create related objects as well. And the ORM doesn't let you mess with auto_now_add fields manually. Mocking the ORM is another option, but not only is it tricky to mock deeply nested ORM methods, but the logic in the ORM code gets mocked out of the test, and mocking seems to make the test really dependent on the internals and dependencies of the function-under-test. The toughest nuts to crack seem to be the functions like this, that sit on a few layers of models and lower-level functions and are very dependent on the time, even though these functions may not be super complicated. My overall problem is that no matter how I seem to slice it, my tests are looking way more complex than the functions they are testing.

  Read the article

• Book review: Peopleware: Productive Projects and Teams

  - by DigiMortal

     Peopleware by Tom DeMarco and Timothy Lister is golden classic book that can be considered as mandatory reading for software project managers, team leads, higher level management and board members of software companies. If you make decisions about people then you cannot miss this book. If you are already good on managing developers then this book can make you even better – you will learn new stuff about successful development teams for sure. Why peopleware? Peopleware gives you very good hints about how to build up working environment for project teams where people can really do their work. Book also covers team building topics that are also important reading. As software developer I found practically all points in this book to be accurate and valid. Many times I have found my self thinking about same things and Peopleware made me more confident about my opinions. Peopleware covers also time management and planning topics that help you do way better job on using developers time effectively by minimizing the amount of interruptions by phone calls, pointless meetings and i-want-to-know-what-are-you-doing-right-now questions by managers who doesn’t write code anyway. I think if you follow suggestions given by Peopleware your developers are very happy. I suggest you to also read another great book – Death March by Edward Yourdon. Death March describes you effectively what happens when good advices given by Peopleware are totally ignored or worse yet – people are treated exactly opposite way. I consider also Death March as golden classics and I strongly recommend you to read this book too. Table of Contents Acknowledgments Preface to the Second Edition Preface to the First Edition Part 1: Managing the Human Resource Chapter 1: Somewhere Today, a Project Is Failing Chapter 2: Make a Cheeseburger, Sell a Cheeseburger Chapter 3: Vienna Waits for You Chapter 4: Quality-If Time Permits Chapter 5: Parkinson's Law Revisited Chapter 6: Laetrile Part II: The Office Environment Chapter 7: The Furniture Police Chapter 8: "You Never Get Anything Done Around Here Between 9 and 5" Chapter 9: Saving Money on Space Intermezzo: Productivity Measurement and Unidentified Flying Objects Chapter 10: Brain Time Versus Body Time Chapter 11: The Telephone Chapter 12: Bring Back the Door Chapter 13: Taking Umbrella Steps Part III: The Right People Chapter 14: The Hornblower Factor Chapter 15: Hiring a Juggler Chapter 16: Happy to Be Here Chapter 17: The Self-Healing System Part IV: Growing Productive Teams Chapter 18: The Whole Is Greater Than the Sum of the Parts Chapter 19: The Black Team Chapter 20: Teamicide Chapter 21: A Spaghetti Dinner Chapter 22: Open Kimono Chapter 23: Chemistry for Team Formation Part V: It't Supposed to Be Fun to Work Here Chapter 24: Chaos and Order Chapter 25: Free Electrons Chapter 26: Holgar Dansk Part VI: Son of Peopleware Chapter 27: Teamicide, Revisited Chapter 28: Competition Chapter 29: Process Improvement Programs Chapter 30: Making Change Possible Chapter 31: Human Capital Chapter 32:Organizational Learning Chapter 33: The Ultimate Management Sin Is Chapter 34: The Making of Community Notes Bibliography Index About the Authors

  Read the article

• Playing with F#

  - by mroberts

  Project Euler is a awesome site.   When working with a new language it can be tricky to find problems that need solving, that are more complex than "Hello World" and simpler than a full blown application. Project Euler gives use just that, cool and thought provoking problems that usually don't take days to solve.  I've solved a number of questions with C# and some with Java.  BTW, I used Java because it had BigInteger support before .Net. A couple weeks ago, back when winter had a firm grip on Columbus, OH, I began playing (researching) with F#.  I began with Problem #1 from Project Euler.  I started by looking at my solution in C#. Here is my solution in C#. 1: using System; 2: using System.Collections.Generic; 3:   4: namespace Problem001 5: { 6: class Program 7: { 8: static void Main(string[] args) 9: { 10: List<int> values = new List<int>(); 11:   12: for (int i = 1; i < 1000; i++) 13: { 14: if (i % 3 == 0 || i % 5 == 0) 15: values.Add(i); 16: } 17: int total = 0; 18:   19: values.ForEach(v => total += v); 20:   21: Console.WriteLine(total); 22: Console.ReadKey(); 23: } 24: } 25: }   Now, after much tweaking and learning, here is my solution in F#.   1: open System 2:   3: let calc n = 4: [1..n] 5: |> List.map (fun x -> if (x % 3 = 0 || x % 5 = 0) then x else 0) 6: |> List.sum 7:   8: let main() = 9: calc 999 10: |> printfn "result = %d" 11: Console.ReadKey(true) |> ignore 12:   13: main() Just this little example highlights some cool things about F#. Type inference. F# infers the type of a value.  In the C# code above we declare a number of variables, the list, and a couple ints.  F# does not require this, it infers the calc (a function) accepts a int and returns a int. Great built in functionality for Lists.  List.map for example. BTW, I don’t think I’m spilling the beans by giving away the code for Problem 1.  It by far is the easiest question, IMHO, solved by 92,000+ people. Next I’ll look into writing a class library with F#.

  Read the article

• A strong component keeps everything together

  - by Justin Paul-Oracle

  Most of the times you implement a WebCenter Content based system, you require some sort of customization. Sometimes these customizations need a Java class or two, or libraries (for example, the JavaMail API), or Database Objects (like new tables, views, indexes, etc). I have seen that libraries and Database Objects are usually put in place using manual steps. This means that the library jar files are copied to one of the common classes directory (set in the Content CLASSPATH variable) and/or the database scripts are executed manually. I have also seen people place the custom Java classes in the common classes directory. While this may seem like an easy solution, think about a scenario where you need to disable or uninstall the component or if you have to upgrade or migrate the system. You have to keep these manual steps documented and execute them every time you encounter the above scenarios. It is very common that some of these manual steps are missed when you have multiple teams and people working on the system. Here are a few points to ponder upon: Place all your custom Java classes within your component. Create a new directory, say ${COMPONENT_DIR}/classes, and place your code there. You can choose to bundle all your classes into a jar or you can place the entire class directory structure. Add a path entry to the Build Settings so that it is bundled with the component when you build it. You also need to update the Custom Class Path and the Custom Class Path Load Order under the Advanced Build Settings. This will ensure that the system CLASSPATH is updated to add this new directory. Create a new component for any new library that you want to add. Add the appropriate path entries to the Build Settings so that it is bundled with the component when you build it. You also need to update the Custom Class Path, Custom Class Path Load Order and/or the Custom Library Path under the Advanced Build Settings. Enter a comma separated list of features that this component will provide. When you create other components that will use the features exposed by this component, make sure that you specify a dependency to this library component by specifying the comma separated list of features in the Advanced Build Settings. The component wizard allows you to create custom install/uninstall Java code. The wizard will create a install filter class when you check the “Has Install” checkbox on the “Install/Uninstall Settings” tab. Consider using this filter class to create database objects when you install the component and drop the objects when you uninstall the component. If you do a lot of custom component development, consider creating a install/uninstall Java class, which can execute queries defined within the component. To sum up, whenever you write a new custom component, make sure that you bundle everything within the component.

  Read the article

• C++11 Tidbits: Decltype (Part 2, trailing return type)

  - by Paolo Carlini

  Following on from last tidbit showing how the decltype operator essentially queries the type of an expression, the second part of this overview discusses how decltype can be syntactically combined with auto (itself the subject of the March 2010 tidbit). This combination can be used to specify trailing return types, also known informally as "late specified return types". Leaving aside the technical jargon, a simple example from section 8.3.5 of the C++11 standard usefully introduces this month's topic. Let's consider a template function like: template <class T, class U> ??? foo(T t, U u) { return t + u; } The question is: what should replace the question marks? The problem is that we are dealing with a template, thus we don't know at the outset the types of T and U. Even if they were restricted to be arithmetic builtin types, non-trivial rules in C++ relate the type of the sum to the types of T and U. In the past - in the GNU C++ runtime library too - programmers used to address these situations by way of rather ugly tricks involving __typeof__ which now, with decltype, could be rewritten as: template <class T, class U> decltype((*(T*)0) + (*(U*)0)) foo(T t, U u) { return t + u; } Of course the latter is guaranteed to work only for builtin arithmetic types, eg, '0' must make sense. In short: it's a hack. On the other hand, in C++11 you can use auto: template <class T, class U> auto foo(T t, U u) -> decltype(t + u) { return t + u; } This is much better. It's generic and a construct fully supported by the language. Finally, let's see a real-life example directly taken from the C++11 runtime library as implemented in GCC: template<typename _IteratorL, typename _IteratorR> inline auto operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) -> decltype(__y.base() - __x.base()) { return __y.base() - __x.base(); } By now it should appear be completely straightforward. The availability of trailing return types in C++11 allowed fixing a real bug in the C++98 implementation of this operator (and many similar ones). In GCC, C++98 mode, this operator is: template<typename _IteratorL, typename _IteratorR> inline typename reverse_iterator<_IteratorL>::difference_type operator-(const reverse_iterator<_IteratorL>& __x, const reverse_iterator<_IteratorR>& __y) { return __y.base() - __x.base(); } This was guaranteed to work well with heterogeneous reverse_iterator types only if difference_type was the same for both types.

  Read the article

• Unknown C# keywords: params

  - by Chris Skardon

  Often overlooked, and (some may say) unloved, is the params keyword, but it’s an awesome keyword, and one you should definitely check out. What does it do? Well, it lets you specify a single parameter that can have a variable number of arguments. You what? Best shown with an example, let’s say we write an add method: public int Add(int first, int second) { return first + second; } meh, it’s alright, does what it says on the tin, but it’s not exactly awe-inspiring… Oh noes! You need to add 3 things together??? public int Add(int first, int second, int third) { return first + second + third; } oh yes, you code master you! Overloading a-plenty! Now a fourth… Ok, this is starting to get a bit ridiculous, if only there was some way… public int Add(int first, int second, params int[] others) { return first + second + others.Sum(); } So now I can call this with any number of int arguments? – well, any number > 2..? Yes! int ret = Add(1, 2, 3); Is as valid as: int ret = Add(1, 2, 3, 4); Of course you probably won’t really need to ever do that method, so what could you use it for? How about adding strings together? What about a logging method? We all know ToString can be an expensive method to call, it might traverse every node on a class hierarchy, or may just be the name of the type… either way, we don’t really want to call it if we can avoid it, so how about a logging method like so: public void Log(LogLevel level, params object[] objs) { if(LoggingLevel < level) return; StringBuilder output = new StringBuilder(); foreach(var obj in objs) output.Append((obj == null) ? "null" : obj.ToString()); return output; } Now we only call ‘ToString’ when we want to, and because we’re passing in just objects we don’t have to call ToString if the Logging Level isn’t what we want… Of course, there are a multitude of things to use params for…

  Read the article

• Why is my dual-boot Ubuntu partition showing up as a peripheral "root.disk"?

  - by Don

  I recently installed Ubuntu 12.04, which I had been booting from a usb key, as a dual-boot on my machine running Windows 7. From what I had read online while researching, I was prepared to have to shrink the Windows partition and all that. But I never had to - it really was just a few clicks here and there and it was installed. I'm still pretty confused about it, but whatever, it worked, and the two peacefully coexist on my machine, and I have broken things to fix before I worry about fixing unbroken things. So yesterday I got it in my head to look at my partitions (I was considering making an all new partition to install the Windows 8 Release Preview). What I saw confused me. Here's a screenshot of the disk utility. At this moment, there is nothing connected to my computer, and nothing in any of the optical drives/ports/card readers/etc. Can you help me figure out what's going on here? Don's Machine is, I believe, my Windows partition - that's the name I assigned my machine from Windows Explorer. PQSERVICE is from what I can find online also Windows, but having to do with backup. And SYSTEM REQUIRED, if I browse it in Ubuntu, is definitely something to do with booting, and I believe it is also Windows'. According to the sizes shown, those three together should use up my 500 GB HD. Then further down, as a "peripheral device", it lists that 31 GB disk. This is obviously my Ubuntu (Model:Linux Loop:root.disk), but why is it showing up as a peripheral? So, to sum up those questions and to add some more random ones I had: Why is Ubuntu showing up as a peripheral device? If the Windows sections take up all 500 GB, where does Ubuntu live? If I renamed the disk partitions, would my life become a nightmare (seriously - can I safely rename them)? Why didn't I have to resize the Windows partition in the first place? Would giving Ubuntu more space improve its performance (it hangs alot)? Is it possible to have a partition for each OS (Windows 7 & 8, Ubuntu), a partition for files, and a separate partition for backups? Is this towards the good or bad idea end of the spectrum? @Elfy, would that explain why it keeps hanging? I guess I'll backup my files, rip it out, and reinstall it correctly later on today.

  Read the article

• How can I be prepared to join a company?

  - by Aerovistae

  There's more to it than that, but this title was the best way I could think of to sum it up. I'm a senior in a good computer science program, and I'm graduating early. About to start interviews and all whatnot. I'm not a super-experienced programmer, not one of those people who started in middle school. I'm decent at this, but I'm not among the best, not nearly. I have to do an awful lot of googling. So today I'm meeting some fellow for lunch at a campus cafe to discuss some front-end details when this tall, good-looking guy begs pardon, says he's new to campus, says he's wondering if we know where he can go to sign up for recruiting developers. Quickly evolves into long conversation: he's the CEO of a seems-to-be-doing-well start-up. Hiring passionate interns and full-times. Sounds great! I take one look at his site on my own computer later, immediately spot a major bug. No idea how to fix it, but I see it. I go over to the page code, and good god. It's the standard amount of code you would expect from a full-scale web application, a couple dozen pages of HTML and scripts. I don't even know where to start reading it. I've built sites from scratch, but obviously never on that scale, nor have I ever worked on one of that scale. I have no idea which bit might generate the bug. But that sets me thinking: How could someone like me possibly settle into an environment like that? A start-up is a very high-pressure working environment. I don't know if I can work at that pace under those constraints-- I would hate to let people down. And with only 10 employees, it's not like anyone has much time to help you get your bearings. Somewhere in there is a question. Can you see it? I'm asking for general advice here. Maybe even anecdotal advice. Is joining a start-up right out of college a scary process? Am I overestimating what it would take to figure out the mass of code behind this site? What's the likelihood a decent but only moderately-experienced coder could earn his pay at such a place? For instance, I know nothing of server-side/back-end programming. Never touched it. That scares me.

  Read the article

• How to make sprint planning fun

  - by Jacob Spire

  Not only are our sprint planning meetings not fun, they're downright dreadful. The meetings are tedious, and boring, and take forever (a day, but it feels like a lot longer). The developers complain about it, and dread upcoming plannings. Our routine is pretty standard (user story inserted into sprint backlog by priority story is taken apart to tasks tasks are estimated in hours repeat), and I can't figure out what we're doing wrong. How can we make the meetings more enjoyable? ... Some more details, in response to requests for more information: Why are the backlog items not inserted and prioritized before sprint kickoff? User stories are indeed prioritized; we have no idea how long they'll take until we break them down into tasks! From the (excellent) answers here, I see that maybe we shouldn't estimate tasks at all, only the user stories. The reason we estimate tasks (and not stories) is because we've been getting story-estimates terribly wrong -- but I guess that's the subject for an altogether different question. Why are developers complaining? Meetings are long. Meetings are monotonous. Story after story, task after task, struggling (yes, struggling) to estimate how long it will take and what it involves. Estimating tasks makes user-story-estimation seem pointless. The longer the meeting, the less focus in the room. The less focused colleagues are, the longer the meeting takes. A recursive hate-spiral develops. We've considered splitting the meeting into two days in order to keep people focused, but the developers wouldn't hear of it. One day of planning is bad enough; now we'll have two?! Part of our problem is that we go into very small detail (in order to get more accurate estimations). But when we estimate roughly, we go way off the mark! To sum up the question: What are we doing wrong? What additional ways are there to make the meeting generally more enjoyable?

  Read the article

• Designing an email system to guarantee delivery

  - by GlenH7

  We are looking to expand our use of email for notification purposes. We understand it will generate more inbox volume, but we are being selective about which events we fire notification on in order to keep the signal-to-noise ratio high. The big question we are struggling with is designing a system that guarantees that the email was delivered. If an email isn't delivered, we will consider that an exception event that needs to be investigated. In reality, I say almost guarantees because there aren't any true guarantees with email. We're just looking for a practical solution to making sure the email got there and experiences others have had with the various approaches to guaranteeing delivery. For the TL;DR crowd - how do we go about designing a system to guarantee delivery of emails? What techniques should we consider so we know the emails were delivered? Our biggest area of concern is what techniques to use so that we know when a message is sent out that it either lands in an inbox or it failed and we need to do something else. Additional requirements: We're not at the stage of including an escalation response, but we'll want that in the future or so we think. Most notifications will be internal to our enterprise, but we will have some notifications being sent to external clients. Some of our application is in a hosted environment. We haven't determined if those servers can access our corporate email servers for relaying or if they'll be acting as their own mail servers. Base design / modules (at the moment): A module to assign tracking identification A module to send out emails A module to receive delivery notification (perhaps this is the same as the email module) A module that checks sent messages against delivery notification and alerts on undelivered email. Some references: Atwood: Send some email Email Tracking Some approaches: Request a response (aka read-receipt or Message Disposition Notification). Seems prone to failure since we have cross-compatibility issues due to differing mail servers and software. Return receipt (aka Delivery Status Notification). Not sure if all mail servers honor this request or not Require an action and therefore prove reply. Seems burdensome to force the recipients to perform an additional task not related to resolving the issue. And no, we haven't come up with a way of linking getting the issue fixed to whether or not the email was received. Force a click-through / Other site sign-in. Similar to requiring some sort of action, this seems like an additional burden and will annoy the users. On the other hand, it seems the most likely to guarantee someone received the notification. Hidden image tracking. Not all email providers automatically load the image, and how would we associate the image(s) with the email tracking ID? Outsource delivery. This gets us out of the email business, but goes back to how to guarantee the out-sourcer's receipt and subsequent delivery to the end recipient. As a related concern, there will be an n:n relationship between issue notification and recipients. The 1 issue : n recipients subset isn't as much of a concern although if we had a delivery failure we would want to investigate and fix the core issue. Of bigger concern is n issues : 1 recipient, and we're specifically concerned in making sure that all n issues were received by the recipient. How does forum software or issue tracking software handle this requirement? If a tracking identifier is used, Where is it placed in the email? In the Subject, or the Body?

  Read the article

• Distinctly LINQ &ndash; Getting a Distinct List of Objects

  - by David Totzke

  Let’s say that you have a list of objects that contains duplicate items and you want to extract a subset of distinct items.  This is pretty straight forward in the trivial case where the duplicate objects are considered the same such as in the following example: List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 }; IEnumerable<int> distinctAges = ages.Distinct(); Console.WriteLine("Distinct ages:"); foreach (int age in distinctAges) { Console.WriteLine(age); } /* This code produces the following output: Distinct ages: 21 46 55 17 */ What if you are working with reference types instead?  Imagine a list of search results where items in the results, while unique in and of themselves, also point to a parent.  We’d like to be able to select a bunch of items in the list but then see only a distinct list of parents.  Distinct isn’t going to help us much on its own as all of the items are distinct already.  Perhaps we can create a class with just the information we are interested in like the Id and Name of the parents.  public class SelectedItem { public int ItemID { get; set; } public string DisplayName { get; set; } } We can then use LINQ to populate a list containing objects with just the information we are interested in and then get rid of the duplicates. IEnumerable<SelectedItem> list = (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>() select new SelectedItem { ItemID = item.ParentId, DisplayName = item.ParentName }) .Distinct(); Most of you will have guessed that this didn’t work.  Even though some of our objects are now duplicates, because we are working with reference types, it doesn’t matter that their properties are the same, they’re still considered unique.  What we need is a way to define equality for the Distinct() extension method. IEqualityComparer<T> Looking at the Distinct method we see that there is an overload that accepts an IEqualityComparer<T>.  We can simply create a class that implements this interface and that allows us to define equality for our SelectedItem class. public class SelectedItemComparer : IEqualityComparer<SelectedItem> { public new bool Equals(SelectedItem abc, SelectedItem def) { return abc.ItemID == def.ItemID && abc.DisplayName == def.DisplayName; } public int GetHashCode(SelectedItem obj) { string code = obj.DisplayName + obj.ItemID.ToString(); return code.GetHashCode(); } } In the Equals method we simply do whatever comparisons are necessary to determine equality and then return true or false.  Take note of the implementation of the GetHashCode method.  GetHashCode must return the same value for two different objects if our Equals method says they are equal.  Get this wrong and your comparer won’t work .  Even though the Equals method returns true, mismatched hash codes will cause the comparison to fail.  For our example, we simply build a string from the properties of the object and then call GetHashCode() on that. Now all we have to do is pass an instance of our IEqualitlyComarer<T> to Distinct and all will be well: IEnumerable<SelectedItem> list =     (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>()         select new SelectedItem { ItemID = item.dahfkp, DisplayName = item.document_code })                         .Distinct(new SelectedItemComparer());   Enjoy. Dave Just because I can… Technorati Tags: LINQ,C#

  Read the article

• GPGPU

  WhatGPU obviously stands for Graphics Processing Unit (the silicon powering the display you are using to read this blog post). The extra GP in front of that stands for General Purpose computing.So, altogether GPGPU refers to computing we can perform on GPU for purposes beyond just drawing on the screen. In effect, we can use a GPGPU a bit like we already use a CPU: to perform some calculation (that doesn’t have to have any visual element to it). The attraction is that a GPGPU can be orders of magnitude faster than a CPU.WhyWhen I was at the SuperComputing conference in Portland last November, GPGPUs were all the rage. A quick online search reveals many articles introducing the GPGPU topic. I'll just share 3 here: pcper (ignoring all pages except the first, it is a good consumer perspective), gizmodo (nice take using mostly layman terms) and vizworld (answering the question on "what's the big deal").The GPGPU programming paradigm (from a high level) is simple: in your CPU program you define functions (aka kernels) that take some input, can perform the costly operation and return the output. The kernels are the things that execute on the GPGPU leveraging its power (and hence execute faster than what they could on the CPU) while the host CPU program waits for the results or asynchronously performs other tasks.However, GPGPUs have different characteristics to CPUs which means they are suitable only for certain classes of problem (i.e. data parallel algorithms) and not for others (e.g. algorithms with branching or recursion or other complex flow control). You also pay a high cost for transferring the input data from the CPU to the GPU (and vice versa the results back to the CPU), so the computation itself has to be long enough to justify the overhead transfer costs. If your problem space fits the criteria then you probably want to check out this technology.HowSo where can you get a graphics card to start playing with all this? At the time of writing, the two main vendors ATI (owned by AMD) and NVIDIA are the obvious players in this industry. You can read about GPGPU on this AMD page and also on this NVIDIA page. NVIDIA's website also has a free chapter on the topic from the "GPU Gems" book: A Toolkit for Computation on GPUs.If you followed the links above, then you've already come across some of the choices of programming models that are available today. Essentially, AMD is offering their ATI Stream technology accessible via a language they call Brook+; NVIDIA offers their CUDA platform which is accessible from CUDA C. Choosing either of those locks you into the GPU vendor and hence your code cannot run on systems with cards from the other vendor (e.g. imagine if your CPU code would run on Intel chips but not AMD chips). Having said that, both vendors plan to support a new emerging standard called OpenCL, which theoretically means your kernels can execute on any GPU that supports it. To learn more about all of these there is a website: gpgpu.org. The caveat about that site is that (currently) it completely ignores the Microsoft approach, which I touch on next.On Windows, there is already a cross-GPU-vendor way of programming GPUs and that is the DirectX API. Specifically, on Windows Vista and Windows 7, the DirectX 11 API offers a dedicated subset of the API for GPGPU programming: DirectCompute. You use this API on the CPU side, to set up and execute the kernels that run on the GPU. The kernels are written in a language called HLSL (High Level Shader Language). You can use DirectCompute with HLSL to write a "compute shader", which is the term DirectX uses for what I've been referring to in this post as a "kernel". For a comprehensive collection of links about this (including tutorials, videos and samples) please see my blog post: DirectCompute.Note that there are many efforts to build even higher level languages on top of DirectX that aim to expose GPGPU programming to a wider audience by making it as easy as today's mainstream programming models. I'll mention here just two of those efforts: Accelerator from MSR and Brahma by Ananth. Comments about this post welcome at the original blog.

  Read the article

• Useful Excel keyboard shortcuts

  - by Ben Lings

  What keyboard shortcuts do you use in Excel? Things I've discovered recently and found very useful are: Shift + Space - select the current row Ctrl + Space - select the current column Ctrl + Shift + Space - select the block of contiguous cell Ctrl + + - Insert (as in the context menu). If the current row is selected, will insert a new row. Ctrl + - - Delete (as in the context menu). If the current row is selected, will delete entire row. What (apart from the normal cut, copy, paste, etc) do you use? Ctrl + 1 to open the Format dialog. Shift + F2 to add/edit a cell comment. Shift + F2, followed by Esc to select the current cell comment, which can then be moved around with the arrow keys (????) or deleted by pressing Del. Ctrl + ???? to move to the last non-blank cell in a series. This is usually the edge of a table, but not if you have blank cells in the path. Pressing End followed by an arrow key does the same thing. Alt + F11 to open the VBA editor. Alt + = to start a SUM() formula and go straight to selecting cells to be summed. Ctrl + G or F5 to jump to a cell by typing its coordinates (e.g. C3) Ctrl + Home to jump to the top left, usually A1 unless you you are in a frozen split view, in which case it will jump to the top left of the "data" area. Ctrl + ; and Ctrl + Shift + ; to insert the current date and time, respectively. I know Ben Lings already posted this one, but I find it indispensable.

  Read the article

• Oracle SQL Developer Data Modeler: What Tables Aren’t In At Least One SubView?

  - by thatjeffsmith

  Organizing your data model makes the information easier to consume. One of the organizational tools provided by Oracle SQL Developer Data Modeler is the ‘SubView.’ In a nutshell, a SubView is a subset of your model. The Challenge: I’ve just created a model which represents my entire ____________ application. We’ll call it ‘residential lending.’ Instead of having all 100+ tables in a single model diagram, I want to break out the tables by module, e.g. appraisals, credit reports, work histories, customers, etc. I’ve spent several hours breaking out the tables to one or more SubViews, but I think i may have missed a few. Is there an easy way to see what tables aren’t in at least ONE subview? The Answer Yes, mostly. The mostly comes about from the way I’m going to accomplish this task. It involves querying the SQL Developer Data Modeler Reporting Schema. So if you don’t have the Reporting Schema setup, you’ll need to do so. Got it? Good, let’s proceed. Before you start querying your Reporting Schema, you might need a data model for the actual reporting schema…meta-meta data! You could reverse engineer the data modeler reporting schema to a new data model, or you could just reference the PDFs in \datamodeler\reports\Reporting Schema diagrams directory. Here’s a hint, it’s THIS one The Query Well, it’s actually going to be at least 2 queries. We need to get a list of distinct designs stored in your repository. For giggles, I’m going to get a listing including each version of the model. So I can query based on design and version, or in this case, timestamp of when it was added to the repository. We’ll get that from the DMRS_DESIGNS table: SELECT DISTINCT design_name, design_ovid, date_published FROM DMRS_designs Then I’m going to feed the design_ovid, down to a subquery for my child report. select name, count(distinct diagram_id) from DMRS_DIAGRAM_ELEMENTS where design_ovid = :dESIGN_OVID and type = 'Table' group by name having count(distinct diagram_id) < 2 order by count(distinct diagram_id) desc Each diagram element has an entry in this table, so I need to filter on type=’Table.’ Each design has AT LEAST one diagram, the master diagram. So any relational table in this table, only having one listing means it’s not in any SubViews. If you have overloaded object names, which is VERY possible, you’ll want to do the report off of ‘OBJECT_ID’, but then you’ll need to correlate that to the NAME, as I doubt you’re so intimate with your designs that you recognize the GUIDs So I’m going to cheat and just stick with names, but I think you get the gist. My Model Of my almost 90 tables, how many of those have I not added to at least one SubView? Now let’s run my report! Voila! My ‘BEER2′ table isn’t in any SubView! It says ’1′ because the main model diagram counts as a view. So if the count came back as ’2′, that would mean the table was in the main model diagram and in 1 SubView diagram. And I know what you’re thinking, what kind of residential lending program would have a table called ‘BEER2?’ Let’s just say, that my business model has some kinks to work out!

  Read the article

< Previous Page | 87 88 89 90 91 92 93 94 95 96 97 98  | Next Page >