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  • Is NAN suitable for communicating that an invalid parameter was involved in a calculation?

    - by Arman
    I am currently working on a numerical processing system that will be deployed in a performance-critical environment. It takes inputs in the form of numerical arrays (these use the eigen library, but for the purpose of this question that's perhaps immaterial), and performs some range of numerical computations (matrix products, concatenations, etc.) to produce outputs. All arrays are allocated statically and their sizes are known at compile time. However, some of the inputs may be invalid. In these exceptional cases, we still want the code to be computed and we still want outputs not "polluted" by invalid values to be used. To give an example, let's take the following trivial example (this is pseudo-code): Matrix a = {1, 2, NAN, 4}; // this is the "input" matrix Scalar b = 2; Matrix output = b * a; // this results in {2, 4, NAN, 8} The idea here is that 2, 4 and 8 are usable values, but the NAN should signal to the receipient of the data that that entry was involved in an operation that involved an invalid value, and should be discarded (this will be detected via a std::isfinite(value) check before the value is used). Is this a sound way of communicating and propagating unusable values, given that performance is critical and heap allocation is not an option (and neither are other resource-consuming constructs such as boost::optional or pointers)? Are there better ways of doing this? At this point I'm quite happy with the current setup but I was hoping to get some fresh ideas or productive criticism of the current implementation.

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  • Term for unit testing that separates test logic from test result data

    - by mario
    So I'm not doing any unit testing. But I've had an idea to make it more appropriate for my field of use. Yet it's not clear if something like this exists, and if, how it would possibly be called. Ordinary unit tests combine the test logic and the expected outcome. In essence the testing framework only checks for booleans (did this match, did the expected result result). To generalize, the test code itself references the audited functions, and also explicites the result values like so: unit::assert( test_me() == 17 ) What I'm looking for is a separation of concerns. The test itself should only contain the tested logic. The outcome and result data should be handled by the unit testing or assertion framework. As example: unit::probe( test_me() ) Here the probe actually doubles as collector in the first run, and afterwards as verification method. The expected 17 is not mentioned in the test code, but stored or managed elsewhere. How is this scheme called? Or how would you call it? I hope I can find some actual implementations with the proper terminology. Obviously such a pattern is unfit for TDD. It's strictly for regression testing. Also obviously, it cannot be used for all cases. Only the simpler test subjects can be analyzed that way, for anything else the ordinary unit test setup and assertion steps are required. And yes, this could be manually accomplished by crafting a ResultWhateverObject, but that would still require hardwiring that to the test logic. Also keep in mind that I'm inquiring for use with scripting languages, and not about Java. I'm aware that the xUnit pattern originates there, and why it's hence as elaborate as it is. Btw, I've discovered one test execution framework which allows for shortening simple test notations to: test_me(); // 17 While thus the result data is no longer coded in (it's a comment), that's still not a complete separation and of course would work only for scalar results.

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  • Performing Aggregate Functions on Multi-Million Row Tables

    - by Daniel Short
    I'm having some serious performance issues with a multi-million row table that I feel I should be able to get results from fairly quick. Here's a run down of what I have, how I'm querying it, and how long it's taking: I'm running SQL Server 2008 Standard, so Partitioning isn't currently an option I'm attempting to aggregate all views for all inventory for a specific account over the last 30 days. All views are stored in the following table: CREATE TABLE [dbo].[LogInvSearches_Daily]( [ID] [bigint] IDENTITY(1,1) NOT NULL, [Inv_ID] [int] NOT NULL, [Site_ID] [int] NOT NULL, [LogCount] [int] NOT NULL, [LogDay] [smalldatetime] NOT NULL, CONSTRAINT [PK_LogInvSearches_Daily] PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY] ) ON [PRIMARY] This table has 132,000,000 records, and is over 4 gigs. A sample of 10 rows from the table: ID Inv_ID Site_ID LogCount LogDay -------------------- ----------- ----------- ----------- ----------------------- 1 486752 48 14 2009-07-21 00:00:00 2 119314 51 16 2009-07-21 00:00:00 3 313678 48 25 2009-07-21 00:00:00 4 298863 0 1 2009-07-21 00:00:00 5 119996 0 2 2009-07-21 00:00:00 6 463777 534 7 2009-07-21 00:00:00 7 339976 503 2 2009-07-21 00:00:00 8 333501 570 4 2009-07-21 00:00:00 9 453955 0 12 2009-07-21 00:00:00 10 443291 0 4 2009-07-21 00:00:00 (10 row(s) affected) I have the following index on LogInvSearches_Daily: /****** Object: Index [IX_LogInvSearches_Daily_LogDay] Script Date: 05/12/2010 11:08:22 ******/ CREATE NONCLUSTERED INDEX [IX_LogInvSearches_Daily_LogDay] ON [dbo].[LogInvSearches_Daily] ( [LogDay] ASC ) INCLUDE ( [Inv_ID], [LogCount]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] I need to pull inventory only from the Inventory for a specific account id. I have an index on the Inventory as well. I'm using the following query to aggregate the data and give me the top 5 records. This query is currently taking 24 seconds to return the 5 rows: StmtText ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- SELECT TOP 5 Sum(LogCount) AS Views , DENSE_RANK() OVER(ORDER BY Sum(LogCount) DESC, Inv_ID DESC) AS Rank , Inv_ID FROM LogInvSearches_Daily D (NOLOCK) WHERE LogDay DateAdd(d, -30, getdate()) AND EXISTS( SELECT NULL FROM propertyControlCenter.dbo.Inventory (NOLOCK) WHERE Acct_ID = 18731 AND Inv_ID = D.Inv_ID ) GROUP BY Inv_ID (1 row(s) affected) StmtText ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |--Top(TOP EXPRESSION:((5))) |--Sequence Project(DEFINE:([Expr1007]=dense_rank)) |--Segment |--Segment |--Sort(ORDER BY:([Expr1006] DESC, [D].[Inv_ID] DESC)) |--Stream Aggregate(GROUP BY:([D].[Inv_ID]) DEFINE:([Expr1006]=SUM([LOALogs].[dbo].[LogInvSearches_Daily].[LogCount] as [D].[LogCount]))) |--Sort(ORDER BY:([D].[Inv_ID] ASC)) |--Nested Loops(Inner Join, OUTER REFERENCES:([D].[Inv_ID])) |--Nested Loops(Inner Join, OUTER REFERENCES:([Expr1011], [Expr1012], [Expr1010])) | |--Compute Scalar(DEFINE:(([Expr1011],[Expr1012],[Expr1010])=GetRangeWithMismatchedTypes(dateadd(day,(-30),getdate()),NULL,(6)))) | | |--Constant Scan | |--Index Seek(OBJECT:([LOALogs].[dbo].[LogInvSearches_Daily].[IX_LogInvSearches_Daily_LogDay] AS [D]), SEEK:([D].[LogDay] > [Expr1011] AND [D].[LogDay] < [Expr1012]) ORDERED FORWARD) |--Index Seek(OBJECT:([propertyControlCenter].[dbo].[Inventory].[IX_Inventory_Acct_ID]), SEEK:([propertyControlCenter].[dbo].[Inventory].[Acct_ID]=(18731) AND [propertyControlCenter].[dbo].[Inventory].[Inv_ID]=[LOA (13 row(s) affected) I tried using a CTE to pick up the rows first and aggregate them, but that didn't run any faster, and gives me essentially the same execution plan. (1 row(s) affected) StmtText ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- --SET SHOWPLAN_TEXT ON; WITH getSearches AS ( SELECT LogCount -- , DENSE_RANK() OVER(ORDER BY Sum(LogCount) DESC, Inv_ID DESC) AS Rank , D.Inv_ID FROM LogInvSearches_Daily D (NOLOCK) INNER JOIN propertyControlCenter.dbo.Inventory I (NOLOCK) ON Acct_ID = 18731 AND I.Inv_ID = D.Inv_ID WHERE LogDay DateAdd(d, -30, getdate()) -- GROUP BY Inv_ID ) SELECT Sum(LogCount) AS Views, Inv_ID FROM getSearches GROUP BY Inv_ID (1 row(s) affected) StmtText ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |--Stream Aggregate(GROUP BY:([D].[Inv_ID]) DEFINE:([Expr1004]=SUM([LOALogs].[dbo].[LogInvSearches_Daily].[LogCount] as [D].[LogCount]))) |--Sort(ORDER BY:([D].[Inv_ID] ASC)) |--Nested Loops(Inner Join, OUTER REFERENCES:([D].[Inv_ID])) |--Nested Loops(Inner Join, OUTER REFERENCES:([Expr1008], [Expr1009], [Expr1007])) | |--Compute Scalar(DEFINE:(([Expr1008],[Expr1009],[Expr1007])=GetRangeWithMismatchedTypes(dateadd(day,(-30),getdate()),NULL,(6)))) | | |--Constant Scan | |--Index Seek(OBJECT:([LOALogs].[dbo].[LogInvSearches_Daily].[IX_LogInvSearches_Daily_LogDay] AS [D]), SEEK:([D].[LogDay] > [Expr1008] AND [D].[LogDay] < [Expr1009]) ORDERED FORWARD) |--Index Seek(OBJECT:([propertyControlCenter].[dbo].[Inventory].[IX_Inventory_Acct_ID] AS [I]), SEEK:([I].[Acct_ID]=(18731) AND [I].[Inv_ID]=[LOALogs].[dbo].[LogInvSearches_Daily].[Inv_ID] as [D].[Inv_ID]) ORDERED FORWARD) (8 row(s) affected) (1 row(s) affected) So given that I'm getting good Index Seeks in my execution plan, what can I do to get this running faster? Thanks, Dan

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  • Update Since Microsoft/PSC Office Open XML Case Study

    - by Tim Murphy
    In 2009 Microsoft released a case study about a project that we had done using the OOXML SDK 1.0 for Research Directors Inc.  Since that time Microsoft has released version 2.0 of the SDK and PSC has done significant development with it.  Below are some of the mile stones we have reached since the original case study. At the time of the original case study two report types had been automated to output as PowerPoint presentations.  Now that the all the main products have been delivered we have added three reports with Word document outputs and five more reports with PowerPoint outputs. One improvement we made over the original application was to create a PowerPoint Add-In which allows the users to tag a slide.  These tags along with the strongly typed SDK 2.0 allows for the code to use LINQ to easily search for slides in the template files.  This allows for a more flexible architecture base on assembling a presentation from copied slide extracted from the template. The new library we created also enabled us to create two new Word based reports in two weeks.  The library we created abstracts the generation of the documents from the business logic and the data retrieval.  The key to this is the mark up.  Content Controls are a good method for identifying sections of a template to be modified or replaced.  Join this with the concept of all data being generically either scalar or two dimensional and the code becomes more generic. In the end we found the OOXML SDK 2.0 to be a great tool for accelerating document generation development and creating happy clients.  del.icio.us Tags: PSC Group,OOXML,Case Study,Office Open XML,Word,PowerPoint

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  • Non use of persisted data – Part deux

    - by Dave Ballantyne
    In my last blog I showed how persisted data may not be used if you have used the base data on an include on an index. That wasn't the only problem ive had that showed the same symptom.  Using the same code as before,  I was executing similar to the below : select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID But,  due to a distribution error in statistics i found it necessary to use a table hint.  In this case, I wanted to force a loop join select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH inner loop join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID   But, being the diligent  TSQL developer that I am ,looking at the execution plan I noticed that the ‘compute scalar’ operator was again calling the function.  Again,  profiler is a more graphic way to view this…..   All very odd,  just because ive forced a join , that has NOTHING, to do with my persisted data then something is causing the data to be re-evaluated. Not sure if there is any easy fix you can do to the TSQL here, but again its a lesson learned (or rather reinforced) examine the execution plan of every query you write to ensure that it is operating as you thought it would.

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  • Implementing Circle Physics in Java

    - by Shijima
    I am working on a simple physics based game where 2 balls bounce off each other. I am following a tutorial, 2-Dimensional Elastic Collisions Without Trigonometry, for the collision reactions. I am using Vector2 from the LIBGDX library to handle vectors. I am a bit confused on how to implement step 6 in Java from the tutorial. Below is my current code, please note that the code strictly follows the tutorial and there are redundant pieces of code which I plan to refactor later. Note: refrences to this refer to ball 1, and ball refers to ball 2. /* * Step 1 * * Find the Normal, Unit Normal and Unit Tangential vectors */ Vector2 n = new Vector2(this.position[0] - ball.position[0], this.position[1] - ball.position[1]); Vector2 un = n.normalize(); Vector2 ut = new Vector2(-un.y, un.x); /* * Step 2 * * Create the initial (before collision) velocity vectors */ Vector2 v1 = this.velocity; Vector2 v2 = ball.velocity; /* * Step 3 * * Resolve the velocity vectors into normal and tangential components */ float v1n = un.dot(v1); float v1t = ut.dot(v1); float v2n = un.dot(v2); float v2t = ut.dot(v2); /* * Step 4 * * Find the new tangential Velocities after collision */ float v1tPrime = v1t; float v2tPrime = v2t; /* * Step 5 * * Find the new normal velocities */ float v1nPrime = v1n * (this.mass - ball.mass) + (2 * ball.mass * v2n) / (this.mass + ball.mass); float v2nPrime = v2n * (ball.mass - this.mass) + (2 * this.mass * v1n) / (this.mass + ball.mass); /* * Step 6 * * Convert the scalar normal and tangential velocities into vectors??? */

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  • Software Installation Failure!

    - by NIKOS ANTONIOU
    I get the same error whenever I try to install software on my laptop, for example: I want to install Pavucontrol. So, I open the terminal and I type sudo apt-get install pavucontrol and my terminal output is: Reading package lists... Done Building dependency tree Reading state information... Done The following extra packages will be installed: libgconfmm-2.6-1c2 libglademm-2.4-1c2a libpulse-mainloop-glib0 padevchooser paman paprefs pavumeter pulseaudio-module-zeroconf The following NEW packages will be installed: libgconfmm-2.6-1c2 libglademm-2.4-1c2a libpulse-mainloop-glib0 padevchooser paman paprefs pavucontrol pavumeter pulseaudio-module-zeroconf 0 upgraded, 9 newly installed, 0 to remove and 172 not upgraded. 1 not fully installed or removed. Need to get 0B/345kB of archives. After this operation, 2044kB of additional disk space will be used. Do you want to continue [Y/n]? Y perl: warning: Setting locale failed. perl: warning: Please check that your locale settings: LANGUAGE = (unset), LC_ALL = (unset), LANG = "el_GR.UTF-8" are supported and installed on your system. perl: warning: Falling back to the standard locale ("C"). Can't exec "locale": No such file or directory at /usr/share/perl5/Debconf/Encoding.pm line 16. Use of uninitialized value $Debconf::Encoding::charmap in scalar chomp at /usr/share/perl5/Debconf/Encoding.pm line 17. dpkg: `ldconfig' not found on PATH. dpkg: 1 expected program(s) not found on PATH. NB: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin. E: Sub-process /usr/bin/dpkg returned an error code (2) What is the problem and how do I fix it?

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  • Problem with SAT collision detection overlap checking code

    - by handyface
    I'm trying to implement a script that detects whether two rotated rectangles collide for my game, using SAT (Separating Axis Theorem). I used the method explained in the following article for my implementation in Google Dart. 2D Rotated Rectangle Collision I tried to implement this code into my game. Basically from what I understood was that I have two rectangles, these two rectangles can produce four axis (two per rectangle) by subtracting adjacent corner coordinates. Then all the corners from both rectangles need to be projected onto each axis, then multiplying the coordinates of the projection by the axis coordinates (point.x*axis.x+point.y*axis.y) to make a scalar value and checking whether the range of both the rectangle's projections overlap. When all the axis have overlapping projections, there's a collision. First of all, I'm wondering whether my comprehension about this algorithm is correct. If so I'd like to get some pointers in where my implementation (written in Dart, which is very readable for people comfortable with C-syntax) goes wrong. Thanks! EDIT: The question has been solved. For those interested in the working implementation: Click here

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  • Cassandra inserts using Net::Cassandra::Easy in Perl

    - by knorv
    When using the Perl module Net::Cassandra::Easy to interface with Cassandra I use the following code to read colums col[123] from rows row[123] in column-family Standard1: my $cassandra = Net::Cassandra::Easy->new(keyspace => 'Keyspace1', server => 'localhost'); $cassandra->connect(); my $result = $cassandra->get(['row1', 'row2', 'row3'], family => 'Standard1', byname => ['col1', 'col2', 'col3']); This works as expected. However, when trying to insert row row1 with .. $result = $cassandra->mutate(['row1'], family => 'Standard1', insertions => { "col1" => "Value to set." }); .. I get the error message Can't use string ("0") as a SCALAR ref while "strict refs" in use at .../Net/GenThrift/Thrift/BinaryProtocol.pm line 376. What am I doing wrong?

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  • How to calculate an angle from three points?

    - by HelloMoon
    Lets say you have this: P1 = (x=2, y=50) P2 = (x=9, y=40) P3 = (x=5, y=20) Assume that P1 is the center point of a circle. It is always the same. I want the angle that is made up by P2 and P3, or in other words the angle that is next to P1. The inner angle to be precise. It will be always a sharp angle, so less than -90 degrees. I thought: Man, that's simplest geometry maths. But I looked for a formula for like 6 hours now and people talk about most complicated NASA stuff like arcos and vector scalar product stuff. My head feels like in a fridge. Some math gurus here that think this is a simple problem? I think the programing language doesn't matter here but for those who think it does: java and objective-c. need that for both. haven't tagged it for these, though.

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  • How to avoid circular relationship in SQL-Server?

    - by Shimmy
    I am creating a self-related table: Table Item columns: ItemId int - PK; Amount money - not null; Price money - a computed column using a UDF that retrieves value according to the items ancestors' Amount. ParentItemId int - nullable, reference to another ItemId in this table. I need to avoid a loop, meaning, a sibling cannot become an ancestor of his ancestors, meaning, if ItemId=2 ParentItemId = 1, then ItemId 1 ParentItemId = 2 shouldn't be allowed. I don't know what should be the best practice in this situation. I think I should add a CK that gets a Scalar value from a UDF or whatever else. EDIT: Another option is to create an INSTEAD OF trigger and put in 1 transaction the update of the ParentItemId field and selecting the Price field from the @@RowIdentity, if it fails cancel transaction, but I would prefer a UDF validating. Any ideas are sincerely welcomed.

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  • 2D Inverse Kinematics Implementation

    - by Vic
    Hi I am trying to implement Inverse Kinematics on a 2D arm(made up of three sticks with joints). I am able to rotate the lowest arm to the desired position. Now, I have some questions: How can I make the upper arm move alongwith the third so the end point of the arm reaches the desired point. Do I need to use the rotation matrices for both and if yes can someone give me some example or an help and is there any other possibl;e way to do this without rotation matrices??? The lowest arm only moves in one direction. I tried google it, they are saying that cross product of two vectors give the direction for the arm but this is for 3D. I am using 2D and cross product of two 2D vectors give a scalar. So, how can I determine its direction??? Plz guys any help would be appreciated.... Thanks in advance Vikram

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  • Saving a select count(*) value to an integer (SQL Server)

    - by larryq
    Hi everyone, I'm having some trouble with this statement, owing no doubt to my ignorance of what is returned from this select statement: declare @myInt as INT set @myInt = (select COUNT(*) from myTable as count) if(@myInt <> 0) begin print 'there's something in the table' end There are records in myTable, but when I run the code above the print statement is never run. Further checks show that myInt is in fact zero after the assignment above. I'm sure I'm missing something, but I assumed that a select count would return a scalar that I could use above?

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  • How do I insert into a unique key into a table?

    - by Ben McCormack
    I want to insert data into a table where I don't know the next unique key that I need. I'm not sure how to format my INSERT query so that the value of the Key field is 1 greater than the maximum value for the key in the table. I know this is a hack, but I'm just running a quick test against a database and need to make sure I always send over a Unique key. Here's the SQL I have so far: INSERT INTO [CMS2000].[dbo].[aDataTypesTest] ([KeyFld] ,[Int1]) VALUES ((SELECT Max([KeyFld]) FROM [dbo].[aDataTypesTest]) + 1 ,1) which errors out with: Msg 1046, Level 15, State 1, Line 5 Subqueries are not allowed in this context. Only scalar expressions are allowed. I'm not able to modify the underlying database table. What do I need to do to ensure a unique insert in my INSERT SQL code?

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  • How do I insert a row with Perl's Net::Cassandra::Easy?

    - by knorv
    When using the Perl module Net::Cassandra::Easy to interface with Cassandra I use the following code to read colums col[123] from rows row[123] in column-family Standard1: my $cassandra = Net::Cassandra::Easy->new(keyspace => 'Keyspace1', server => 'localhost'); $cassandra->connect(); my $result = $cassandra->get(['row1', 'row2', 'row3'], family => 'Standard1', byname => ['col1', 'col2', 'col3']); This works as expected. However, when trying to insert row row1 with .. $result = $cassandra->mutate(['row1'], family => 'Standard1', insertions => { "col1" => "Value to set." }); .. I get the error message Can't use string ("0") as a SCALAR ref while "strict refs" in use at .../Net/GenThrift/Thrift/BinaryProtocol.pm line 376. What am I doing wrong?

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  • Entity Framework - Using a list as a paramater in a compiled query

    - by vdh_ant
    Hi guys Just wondering if anyone knows whether I should be able to pass in list into a compiled query and have the query perform a contains operation? The reason why I ask is that I have a scenario where I need to do this, yet at run time I am getting the following error... The specified parameter 'categories' of type 'System.Collections.Generic.List`1[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' is not valid. Only scalar parameters (such as Int32, Decimal, and Guid) are supported. I can understand why this might be the case but I was wondering if anyone knows a way around it. Cheers Anthony

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  • Why doesn't my Perl code work when I put it in a foreach loop?

    - by foxhop
    This code outputs the scalars in the row array properly: $line = "This is my favorite test"; @row = split(/ /, $line); print $row[0]; print $row[1]; The same code inside a foreach loop doesn't print any scalar values: foreach $line (@lines){ @row = split(/ /, $line); print $row[0]; print $row[1]; } What could cause this to happen? I am new to Perl coming from python. I need to learn Perl for my new position.

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  • Can't access stored procedure from entities

    - by molgan
    Hello I'm using entity framework that came with 3.5sp1. And in visual studio I have imported function so it shows under "Function Imports" in the "Model Browser". I have assigned all rights to the user that connects to the database. But it doesnt show in the intellisense when I type "_entities.", only my other entities shows there. I opened the designer file and couldnt find it there either..... The stored procedure should return a scalar datetime value, and not an "entity" What might be wrong here? /M

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  • Mapping functions of 2D numpy arrays

    - by perimosocordiae
    I have a function foo that takes a NxM numpy array as an argument and returns a scalar value. I have a AxNxM numpy array data, over which I'd like to map foo to give me a resultant numpy array of length A. Curently, I'm doing this: result = numpy.array([foo(x) for x in data]) It works, but it seems like I'm not taking advantage of the numpy magic (and speed). Is there a better way? I've looked at numpy.vectorize, and numpy.apply_along_axis, but neither works for a function of 2D arrays. EDIT: I'm doing boosted regression on 24x24 image patches, so my AxNxM is something like 1000x24x24. What I called foo above applies a Haar-like feature to a patch (so, not terribly computationally intensive).

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  • How to change handedness of coordinates?

    - by 742
    How to convert from Euler's coordinates E1 = (x1, y1, z1, yaw1, pitch1, roll1) to E2 = (x2, y2, z2, yaw2, pitch2, roll2) where x, y, z are the coordinates of a point and yaw, pitch, roll the direction/orientation of a vector which origin is the point. yaw is around y, pitch around x, roll around z. They are performed in that order. Yaw 0 is normal to the plan xy (opposite to z in E1 and equal to z in E2). E1 uses a right handed space and E2 a left handed space. Both have the same origin, the same direction for y (top) and z (into the screen). They differ by x which is to the left on E1 and to the right on E2. They also differ by their direction of positive rotations. I've a custom type to hold the scalar representation and to convert from and to the equivalent WPF Matrix3d representation.

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  • Arrays of pointers to arrays?

    - by a2h
    I'm using a library which for one certain feature involves variables like so: extern const u8 foo[]; extern const u8 bar[]; I am not allowed to rename these variables in any way. However, I like to be able to access these variables through an array (or other similar method) so that I do not need to continually hardcode new instances of these variables into my main code. My first attempt at creating an array is as follows: const u8* pl[] = { &foo, &bar }; This gave me the error cannot convert 'const u8 (*)[]' to 'const u8*' in initialization, and with help elsewhere along with some Googling, I changed my array to this: u8 (*pl)[] = { &foo, &bar }; Upon compiling I now get the error scalar object 'pl' requires one element in initializer. Does anyone have any ideas on what I'm doing wrong? Thanks.

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  • Matlab tutorial for programmers

    - by Jonas
    I'm getting some new students soon, who will be writing Matlab code. They're new to Matlab, but they have experience coding in Java and C++. I'm going to have them go through the 'Getting Started' section of the Matlab help. In addition, I want to give a small tutorial with the goal to prevent them from making some of the most common mistakes people make when switching to Matlab ("Matlab starts counting at 1"), and show them some features that they may not be aware of when coming from other languages ("you can subtract a scalar directly from an array, and for vectors, there's bsxfun"). What are the most important things I should tell them?

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  • What is wrong with this database query?

    - by outsyncof
    I have the following tables in a database (i'll only list the important attributes): Person(ssn,countryofbirth) Parents(ssn,fatherbirthcountry) Employment(ssn, companyID) Company(companyID, name) My task is this: given fatherbirthcountry as input, output the names of companies where persons work whose countryofbirth match the fatherbirthcountry input. I pretend that the fatherbirthcountry is Mexico and do this: SELECT name FROM Company WHERE companyid = (SELECT companyid FROM Employment WHERE ssn = (SELECT ssn FROM Person WHERE countryofbirth = 'Mexico'); but it is giving me an error: >Scalar subquery is only allowed to return a single row. am I completely off track? Can anybody please help?

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  • Variable alpha blending in pylab

    - by Hooked
    How does one control the transparency over a 2D image in pylab? I'd like to give two sets of values (X,Y,Z,T) where X,Y are arrays of positions, Z is the color value, and T is the transparency to a function like imshow but it seems that the function only takes alpha as a scalar. As a concrete example, consider the code below that attempts to display two Gaussians. The closer the value is to zero, the more transparent I'd like the plot to be. from pylab import * side = linspace(-1,1,100) X,Y = meshgrid(side,side) extent = (-1,1,-1,1) Z1 = exp(-((X+.5)**2+Y**2)) Z2 = exp(-((X-.5)**2+(Y+.2)**2)) imshow(Z1, cmap=cm.hsv, alpha=.6, extent=extent) imshow(Z2, cmap=cm.hsv, alpha=.6, extent=extent) show() Note: I am not looking for a plot of Z1+Z2 (that would be trivial) but for a general way to specify the alpha blending across an image.

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  • Argument passing regarding ivars

    - by StoneBreaker
    I am passing an iVar into a function. The iVar is a double. The value of the iVar inside the function is correct, but the value of the iVar outside the function is not changed. This must have something to do with the way that I am receiving the iVar into the function. How do I pass a double iVar in so that its value is changed in the object and not only in the function? I do the same thing with pointers and the results are as expected, so I think I am not understanding scalar argument passing in c/objective-c.

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