c++,matlab,linear-algebra,eigen,intel-mkl , Rewriting Matlab eig(A,B) (Generalized eigenvalues/eigenvectors) to C/C++

## Question:

Tag: c++,matlab,linear-algebra,eigen,intel-mkl

Do anyone have any idea how can I rewrite `eig(A,B)` from Matlab used to calculate generalized eigenvector/eigenvalues? I've been struggling with this problem lately. So far:

Matlab definition of `eig` function I need:

``````[V,D] = eig(A,B) produces a diagonal matrix D of generalized
eigenvalues and a full matrix V whose columns are the corresponding
eigenvectors so that A*V = B*V*D.
``````
1. So far I tried the `Eigen` library (http://eigen.tuxfamily.org/dox/classEigen_1_1GeneralizedSelfAdjointEigenSolver.html)

My implementation looks like this:

``````std::pair<Matrix4cd, Vector4d> eig(const Matrix4cd& A, const Matrix4cd& B)
{

Matrix4cd V = solver.eigenvectors();
Vector4d D = solver.eigenvalues();

return std::make_pair(V, D);
}
``````

But first thing that comes to my mind is, that I can't use `Vector4cd` as `.eigenvalues()` doesn't return complex values where Matlab does. Furthermore results of `.eigenvectors()` and `.eigenvalues()` for the same matrices are not the same at all:

C++:

``````Matrix4cd x;
Matrix4cd y;
pair<Matrix4cd, Vector4d> result;

for (int i = 0; i < 4; i++)
{
for (int j = 0; j < 4; j++)
{
x.real()(i,j) = (double)(i+j+1+i*3);
y.real()(i,j) = (double)(17 - (i+j+1+i*3));

x.imag()(i,j) = (double)(i+j+1+i*3);
y.imag()(i,j) = (double)(17 - (i+j+1+i*3));
}
}
result = eig(x,y);
cout << result.first << endl << endl;
cout << result.second << endl << endl;
``````

Matlab:

``````for i=1:1:4
for j=1:1:4
x(i,j) = complex((i-1)+(j-1)+1+((i-1)*3), (i-1)+(j-1)+1+((i-1)*3));
y(i,j) = complex(17 - ((i-1)+(j-1)+1+((i-1)*3)), 17 - ((i-1)+(j-1)+1+((i-1)*3)));
end
end

[A,B] = eig(x,y)
``````

So I give `eig` the same 4x4 matrices holding values 1-16 ascending (x) and descending (y). But I receive different results, furthermore `Eigen` method returns double from eigenvalues while Matlab returns complex dobule. I also find out that there is other `Eigen` solver named `GeneralizedEigenSolver`. That one in the documentation (http://eigen.tuxfamily.org/dox/classEigen_1_1GeneralizedEigenSolver.html) has written that it solves `A*V = B*V*D` but to be honest I tried it and results (matrix sizes) are not the same size as Matlab so I got quite lost how it works (examplary results are on the website I've linked). It also has only .eigenvector method.

C++ results:

``````(-0.222268,-0.0108754) (0.0803437,-0.0254809) (0.0383264,-0.0233819) (0.0995482,0.00682079)
(-0.009275,-0.0182668) (-0.0395551,-0.0582127) (0.0550395,0.03434) (-0.034419,-0.0287563)
(-0.112716,-0.0621061) (-0.010788,0.10297) (-0.0820552,0.0294896) (-0.114596,-0.146384)
(0.28873,0.257988) (0.0166259,-0.0529934) (0.0351645,-0.0322988) (0.405394,0.424698)

-1.66983
-0.0733194
0.0386832
3.97933
``````

Matlab results:

``````[A,B] = eig(x,y)

A =

Columns 1 through 3

-0.9100 + 0.0900i  -0.5506 + 0.4494i   0.3614 + 0.3531i
0.7123 + 0.0734i   0.4928 - 0.2586i  -0.5663 - 0.4337i
0.0899 - 0.4170i  -0.1210 - 0.3087i   0.0484 - 0.1918i
0.1077 + 0.2535i   0.1787 + 0.1179i   0.1565 + 0.2724i

Column 4

-0.3237 - 0.3868i
0.2338 + 0.7662i
0.5036 - 0.3720i
-0.4136 - 0.0074i

B =

Columns 1 through 3

-1.0000 + 0.0000i   0.0000 + 0.0000i   0.0000 + 0.0000i
0.0000 + 0.0000i  -1.0000 - 0.0000i   0.0000 + 0.0000i
0.0000 + 0.0000i   0.0000 + 0.0000i  -4.5745 - 1.8929i
0.0000 + 0.0000i   0.0000 + 0.0000i   0.0000 + 0.0000i

Column 4

0.0000 + 0.0000i
0.0000 + 0.0000i
0.0000 + 0.0000i
-0.3317 + 1.1948i
``````
1. Second try was with Intel IPP but it seems that it solves only `A*V = V*D` and support told me that it's not supported anymore.

https://software.intel.com/en-us/node/505270 (list of constructors for Intel IPP)

1. I got suggestion to move from Intel IPP to MKL. I did it and hit the wall again. I tried to check all algorithms for `Eigen` but it seems that there are only `A*V = V*D` problems solved. I was checking `lapack95.lib`. The list of algorithms used by this library is available there: https://software.intel.com/sites/products/documentation/doclib/mkl_sa/11/mkl_lapack_examples/index.htm#dsyev.htm

Somewhere on the web I could find topic on Mathworks when someone said that managed to solve my problem partially with usage of MKL:

Person said that he/she used `dsygv` algorithm but I can't locate anything like that on the web. Maybe it's a typo.

Anyone has any other proposition/idea how can I implement it? Or maybe point my mistake. I'd appreciate that.

EDIT: In comments I've received a hint that I was using `Eigen` solver wrong. My `A` matrix wasn't self-adjoint and my `B` matrix wasn't positive-definite. I took matrices from program I want to rewrite to C++ (from random iteration) and checked if they meet the requirements. They did:

``````Rj =

1.0e+02 *

Columns 1 through 3

0.1302 + 0.0000i  -0.0153 + 0.0724i   0.0011 - 0.0042i
-0.0153 - 0.0724i   1.2041 + 0.0000i  -0.0524 + 0.0377i
0.0011 + 0.0042i  -0.0524 - 0.0377i   0.0477 + 0.0000i
-0.0080 - 0.0108i   0.0929 - 0.0115i  -0.0055 + 0.0021i

Column 4

-0.0080 + 0.0108i
0.0929 + 0.0115i
-0.0055 - 0.0021i
0.0317 + 0.0000i

Rt =

Columns 1 through 3

4.8156 + 0.0000i  -0.3397 + 1.3502i  -0.2143 - 0.3593i
-0.3397 - 1.3502i   7.3635 + 0.0000i  -0.5539 - 0.5176i
-0.2143 + 0.3593i  -0.5539 + 0.5176i   1.7801 + 0.0000i
0.5241 + 0.9105i   0.9514 + 0.6572i  -0.7302 + 0.3161i

Column 4

0.5241 - 0.9105i
0.9514 - 0.6572i
-0.7302 - 0.3161i
9.6022 + 0.0000i
``````

As for `Rj` which is now my `A` - it is self-adjoint because `Rj = Rj'` and `Rj = ctranspose(Rj)`. (http://mathworld.wolfram.com/Self-AdjointMatrix.html)

As for `Rt` which is now my `B` - it is Positive-Definite what is checked with method linked to me. (http://www.mathworks.com/matlabcentral/answers/101132-how-do-i-determine-if-a-matrix-is-positive-definite-using-matlab). So

``````>> [~,p] = chol(Rt)

p =

0
``````

I've rewritten matrices manually to C++ and performed `eig(A,B)` again with matrices meeting requirements:

``````Matrix4cd x;
Matrix4cd y;
pair<Matrix4cd, Vector4d> result;

x.real()(0,0) = 13.0163601949795;
x.real()(0,1) = -1.53172561296005;
x.real()(0,2) = 0.109594869350436;
x.real()(0,3) = -0.804231869422614;

x.real()(1,0) = -1.53172561296005;
x.real()(1,1) = 120.406645675346;
x.real()(1,2) = -5.23758765476463;
x.real()(1,3) = 9.28686785230169;

x.real()(2,0) = 0.109594869350436;
x.real()(2,1) = -5.23758765476463;
x.real()(2,2) = 4.76648319080400;
x.real()(2,3) = -0.552823839520508;

x.real()(3,0) = -0.804231869422614;
x.real()(3,1) = 9.28686785230169;
x.real()(3,2) = -0.552823839520508;
x.real()(3,3) = 3.16510496622613;

x.imag()(0,0) = -0.00000000000000;
x.imag()(0,1) = 7.23946944213164;
x.imag()(0,2) = 0.419181335323979;
x.imag()(0,3) = 1.08441894337449;

x.imag()(1,0) = -7.23946944213164;
x.imag()(1,1) = -0.00000000000000;
x.imag()(1,2) = 3.76849276970080;
x.imag()(1,3) = 1.14635625342266;

x.imag()(2,0) = 0.419181335323979;
x.imag()(2,1) = -3.76849276970080;
x.imag()(2,2) = -0.00000000000000;
x.imag()(2,3) = 0.205129702522089;

x.imag()(3,0) = -1.08441894337449;
x.imag()(3,1) = -1.14635625342266;
x.imag()(3,2) = 0.205129702522089;
x.imag()(3,3) = -0.00000000000000;

y.real()(0,0) = 4.81562784930907;
y.real()(0,1) = -0.339731222392148;
y.real()(0,2) = -0.214319720979258;
y.real()(0,3) = 0.524107127885349;

y.real()(1,0) = -0.339731222392148;
y.real()(1,1) = 7.36354235698375;
y.real()(1,2) = -0.553927983436786;
y.real()(1,3) = 0.951404408649307;

y.real()(2,0) = -0.214319720979258;
y.real()(2,1) = -0.553927983436786;
y.real()(2,2) = 1.78008768533745;
y.real()(2,3) = -0.730246631850385;

y.real()(3,0) = 0.524107127885349;
y.real()(3,1) = 0.951404408649307;
y.real()(3,2) = -0.730246631850385;
y.real()(3,3) = 9.60215057284395;

y.imag()(0,0) = -0.00000000000000;
y.imag()(0,1) = 1.35016928394966;
y.imag()(0,2) = -0.359262708214312;
y.imag()(0,3) = -0.910512495060186;

y.imag()(1,0) = -1.35016928394966;
y.imag()(1,1) = -0.00000000000000;
y.imag()(1,2) = -0.517616473138836;
y.imag()(1,3) = -0.657235460367660;

y.imag()(2,0) = 0.359262708214312;
y.imag()(2,1) = 0.517616473138836;
y.imag()(2,2) = -0.00000000000000;
y.imag()(2,3) = -0.316090662865005;

y.imag()(3,0) = 0.910512495060186;
y.imag()(3,1) = 0.657235460367660;
y.imag()(3,2) = 0.316090662865005;
y.imag()(3,3) = -0.00000000000000;

result = eig(x,y);

cout << result.first << endl << endl;
cout << result.second << endl << endl;
``````

And the results of C++:

``````(0.0295948,0.00562174) (-0.253532,0.0138373) (-0.395087,-0.0139696) (-0.0918132,-0.0788735)
(-0.00994614,-0.0213973) (-0.0118322,-0.0445976) (0.00993512,0.0127006) (0.0590018,-0.387949)
(0.0139485,-0.00832193) (0.363694,-0.446652) (-0.319168,0.376483) (-0.234447,-0.0859585)
(0.173697,0.268015) (0.0279387,-0.0103741) (0.0273701,0.0937148)  (-0.055169,0.0295393)

0.244233
2.24309
3.24152
18.664
``````

Results of MATLAB:

``````>>  [A,B] = eig(Rj,Rt)

A =

Columns 1 through 3

0.0208 - 0.0218i   0.2425 + 0.0753i  -0.1242 + 0.3753i
-0.0234 - 0.0033i  -0.0044 + 0.0459i   0.0150 - 0.0060i
0.0006 - 0.0162i  -0.4964 + 0.2921i   0.2719 + 0.4119i
0.3194 + 0.0000i  -0.0298 + 0.0000i   0.0976 + 0.0000i

Column 4

-0.0437 - 0.1129i
0.2351 - 0.3142i
-0.1661 - 0.1864i
-0.0626 + 0.0000i

B =

0.2442         0         0         0
0    2.2431         0         0
0         0    3.2415         0
0         0         0   18.6640
``````

`Eigenvalues` are the same! Nice, but why `Eigenvectors` are not similar at all?

There is no problem here with Eigen.

In fact for the second example run, Matlab and Eigen produced the very same result. Please remember from basic linear algebra that eigenvector are determined up to an arbitrary scaling factor. (I.e. if v is an eigenvector the same holds for alpha*v, where alpha is a non zero complex scalar.)

It is quite common that different linear algebra libraries compute different eigenvectors, but this does not mean that one of the two codes is wrong: it simply means that they choose a different scaling of the eigenvectors.

EDIT

The main problem with exactly replicating the scaling chosen by matlab is that `eig(A,B)` is a driver routine, which depending from the different properties of `A` and `B` may call different libraries/routines, and apply extra steps like balancing the matrices and so on. By quickly inspecting your example, I would say that in this case matlab is enforcing following condition:

• `all(imag(V(end,:))==0)` (the last component of each eigenvector is real)

but not imposing other constraints. This unfortunately means that the scaling is not unique, and probably depends on intermediate results of the generalised eigenvector algorithm used. In this case I'm not able to give you advice on how to exactly replicate matlab: knowledge of the internal working of matlab is required.

As a general remark, in linear algebra usually one does not care too much about eigenvector scaling, since this is usually completely irrelevant for the problem solved, when the eigenvectors are just used as intermediate results.

The only case in which the scaling has to be defined exactly, is when you are going to give a graphic representation of the eigenvalues.

# Related:

## Passing something as this argument discards qualifiers

c++,c++11
Using the below code, i get the following compile error: In static member function ‘static std::string ctedata::Record::getDispatcher<std::basic_string<char> >::impl(const ctedata::Record&, const string&)’: /home/jason/CrownTheEmpire/lib/ctedata/data.h:111:38: error: passing ‘const std::map<std::basic_string<char>, std::basic_string<char> >’ as ‘this’ argument discards qualifiers [-fpermissive] return rec.fieldValues_[field]; ^ In file included from /usr/include/c++/5.1.0/map:61:0, from...

## Can python script know the return value of C++ main function in the Android enviroment

python,c++
There are several ways of calling C++ executable programs. For example, we can use def run_exe_return_code(run_cmd): process=subprocess.Popen(run_cmd,stdout=subprocess.PIPE,shell=True) (output,err)=process.communicate() exit_code = process.wait() print output print err print exit_code return exit_code to process a C++ executable program: run_exe_return_code('abc') while abc is created by the following C++ codes: int main() { return 1;...

## 3 X 3 magic square recursively

c++,algorithm,math,recursion
I'm trying to find all possible solutions to the 3X3 magic square. There should be exactly 8 solutions. My code gets them all but there are a lot of repeats. I'm having a hard time tracking the recursive steps to see why I'm getting all the repeats. // This program...

## Why black surf from this Matlab command?

matlab,time-frequency
Code tfr = abs ( tfr ); [row_size, column_size] = size(tfr); tfr = tfr(1:round(row_size/2), 1:row_size); surf(tfr); view(2); I get in R2014b of OSX 10.10.3 Yosemite but rotating around shows that the cells should not be black Why is the output black? I wonder if this is a hardware problem or...

## MFC visual c++ LNK2019 link error

c++,mfc
I just don't understand why i can use the public variables on the class but are getting a link error when trying to use the getLicenceRefused method. I wasn't sure if the problem was because of the CString copy constructor problem I have had before so took the parameter out,...

## How can I convert an int to a string in C++11 without using to_string or stoi?

c++,string,c++11,gcc
I know it sounds stupid, but I'm using MinGW32 on Windows7, and "to_string was not declared in this scope." It's an actual GCC Bug, and I've followed these instructions and they did not work. So, how can I convert an int to a string in C++11 without using to_string or...

## Copy text and placeholders, variables to the clipboard

c++,qt,clipboard
In my application I want generate random numbers or strings with a text in front of it. It is important for me that the text won't appear in my window, but instead gets copied to the clipboard. int randomnumber = rand() % 46 + 1; QClipboard *cb = QApplication::clipboard(); cb->setText("Just...

## create vector of objects on the stack ? (c++)

c++,vector,heap-memory
I am creating a temporary vector of pointers to myObject objects. But I am wondering about what happens to the objects I created... { std::vector<myObject *> myVector; myVector.reserve(5); for (int i = 0 ; i < 5 ; ++i){ myVector[i] = new myObject(); } } I assume that at the...

## pointer to pointer dynamic array in C++

c++,arrays,pointers
I've been having bad luck with dynamic pointers when I want to close it. why the application wrote to memory after end of heap buffer? how can I close my array? int main() { . . int **W; W = new int* [n]; for (int i=1; i <= n; i++)...

## Validate case pattern (isupper/islower) on user input string

c++,user-input
I need to write a program that checks if the user-provided first and last names are correctly typed. The program needs to validate that only the first letter of each name part is uppercase. I managed to write code that checks the first character of the input. So I have...

## How can I access the members of a subclass from a superclass with a different constructor?

c++,inheritance,constructor,subclass,superclass
I have the following class and typedef: class Object { protected: long int id; public: Object(void); ~Object(void) {}; long int get_id(void); }; typedef map<string, Object> obj_map; And then I have its child: class Image: public Object { private: path full_path; int x; int y; img image; public: Image(path p, int...

## Plot multiple functions on one figure

matlab,matlab-figure
I'm struggling to plot multiple functions on one figure. Here is the code that I have: syms t a; a=0.9514; F1=0.5*sqrt(3*t^2); F2=-0.28375*t^2+1.155*a*(t-a)+1; F3=1; E1=diff(F1,t); E2=diff(F2,t); E3=diff(F3,t); I want to plot E1, E2 and E3, each only within a certain range, to make a "composite" line. I've tried plotting with ezplot...

## undefined reference to `vtable for implementation' error

c++,build,makefile
I wrote some c++ files and after compiling with out make file it works fine . But when using make file it pop out some errors . My codes are : include directory files : application.h #ifndef APPLICATION_H #define APPLICATION_H #include "employee.h" #include "employee_data.h" #include "employee.h" ...some defintions here... #endif...

## C++ & Qt: Random string from an array area

c++,arrays,string,qt,random
In my small Qt application, I want to pick a random string out of an array after I clicked on a button. I've read many threads but nothing works for me. So in my slot there's an array with several strings in it. I also implemented <string>, <time.h> and srand....

## Translating a character array into a integer string in C++

c++,arrays,string
I was trying to achieve translating a character array into a integer string and corresponding character to their alphabetical order. For instance: A(a) = 0 , Z(z) = 25. string key_char = argv[1]; string key_num; for (int i = 0; i < key_char.length(); i++){ if (isalpha(key_char[i])){ if (islower(key_char[i])){ key_num[i] =...

## Issue when use two type-cast operators in template class

c++
I define a template class in which, I define two type-cast operator template <class base_t> struct subclass { base_t base; //any function which defined for 'base_t' can be used with 'subclass<base_t>' operator base_t&() { return base; } //I want 'subclass<base_t>' can be converted to any class which 'base_t' can //I...

## Type function that returns a tuple of chosen types

c++,templates,c++11,metaprogramming
I've implemented a type function Tuple that turn a list of My_enum values into an std::tuple of corresponding types: #include <tuple> enum My_enum{ t_int, t_double }; // Bind_type is a type function that given a My_enum returns the corresponding type template<My_enum E> struct Bind_type; template<> struct Bind_type<t_int>{ using type =...

## How to access variables in the properties block of a Matlab System Object?

I am working on a simple System Object in Matlab/Simulink. It looks like this : classdef realtime_header_detectorSO < matlab.System & matlab.system.mixin.Propagates % correlateHeader % % This template includes the minimum set of functions required % to define a System object with discrete state. properties Header %nrOfBitsInPreviousStep=0; s=100; d=zeros(1,s); end properties...

## .cpp:23: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘int atoi(const char*)’

c++,string
Here a basic code I'm trying to run But I'm having trouble with stoi (it's c++) I keep getting error: ‘stoi’ was not declared in this scope I tried atoi and strtol with this error .cpp:23: error: cannot convert ‘std::string’ to ‘const char*’ for argument ‘1’ to ‘int atoi(const char*)’...

## Test if string represents “yyyy-mm-dd”

c++,command-line-arguments
I am working on a program that takes two command line arguments. Both arguments should be dates of the form yyyy-mm-dd. Since other folks will be using this program and it will be requesting from mysql, I want to make sure that the command line arguments are valid. My original...

## Strings vs binary for storing variables inside the file format

c++,file,hdf5,dataformat
We aim at using HDF5 for our data format. HDF5 has been selected because it is a hierarchical filesystem-like cross-platform data format and it supports large amounts of data. The file will contain arrays and some parameters. The question is about how to store the parameters (which are not made...

## OpenCV - Detection of moving object C++

c++,opencv
I am working on Traffic Surveillance System an OpenCv project, I need to detect moving cars and people. I am using background subtraction method to detect moving objects and thus drawing counters. I have a problem : When two car are moving on road closely them my system detects it...

## Confused about returns in stack template

c++,templates,generic-programming
I'm implementing a generic stack (with an array) in C++ and am confused about what to return in this situation: template <class T> T Stack<T>::pop(void) { if (size != 0) { return items[size - 1]; size--; } else { cerr << "Cannot pop from empty stack." << endl; return ???;...

## Connecting two binary objects in matlab

matlab,image-processing
I have a binary matrix containing several binary objects and I want to bridge between them. Actually I have the following picture: And the result has to be like this: Is there any function or a shortcut way, other than loops, for this problem?...

## matlab plots as movie with legend

matlab,plot,legend,movie
i have a question regarding legend for movies. This is my code: fig = figure(); for i = 1: 70000 plot(signal1) hold on; plot([i,i],[-5,5]) plot(signal2,'r') hold off; title('\fontsize{14} my data'); legend('signal1','signal2'); axis tight; f(i) = getframe(fig); end The legend shows the same colors for the first two things I plot....

## Interpolation inside a matrix. Matlab

matlab,matrix
I have a matrix looks like: 0 0 0 0 0 1 0 0 0 0 0 2 0 0 0 0 0 2 0 0 0 0 0 1 0 1 0 0 0 1 0 4 0 0 0 0 0 3 0 0 6 0 0 4...

## Method returning std::vector>

c++
As a continuation of a: Thread, I came across a problem with writing a method of a class which returns: std::vector<std::unique_ptr<Object>> I get compiler errors when such a return type is written. There is some problem with delete operand or something ... Generally, I've wanted to write a method which...

## How to switch Matlab plot tick labels to scientific form?

matlab,plot
I have a semilogarithmic plot which works so far with semilogx. Now I would like to change the tick labels. Now it says 10^8 10^9 ... 10^13, but I would like to see 1e8, 1e9, ... 1e13 on the x-axis. How can I change that? Cheers Manuel...

## C++ Isn't this a useless inline declaration?

c++,inline,private,member,protected
This is another question about inlining a function. But I will take possible comments and answers right away: Defining a function inside a class makes it inline automatically. The same behaviour can be achieved by marking a function with inline outside of the class. An inline function doesn't have to...

## How to force my output data in a inputdlg on Matlab be a double?

matlab,typeconverter
I'm currently using a MATLAB to work and I need some help: I need to convert my output data (variable: units) be a double instead of a cell because I must perform a sum: units = inputdlg(question,title); sum = units + i; I've tried this code also but didn't solve...

## Same function with and without template

c++,c++11
I am trying to understand a piece of code of C++11. A class contains 2 functions as shown below: class abc { public: void integerA(int x); template<typename typ> void integerA(typ x); }; I am unable to understand benefit of declaring 2 same functions. Why not declare only one template function?...

## How to normalise polynomial coefficients in a fraction?

matlab,polynomial-math
I have the following code: syms z Gc=1.582*(1-0.3679*z^-1)/(1+.418*z^-1); Ghp=.3679*(z^-1)*(1+.718*z^-1)/((1-z^-1)*(1-.3679*z^-1)); T=(Gc*Ghp)/(1+Gc*Ghp); clipboard('copy', latex(simplifyFraction(T))); Which results in following for T: How can I normalise coefficients? I.e. I want the z2 in denominator and z in numerator to have the coefficient of 1. Is there any function in Matlab to do so?...

## Add more features to stack container

c++,visual-c++,stl
I am using default features(push, pop, top, empty, size) of stack container of STL. If I want to add more features like access an element from middle of stack. How could I do this? Thanks...

## How can I tell clang-format to follow this convention?

c++,clang-format
I would like to have this: if (!enabled) { return; } turned to this: if (!enabled) { return; } (In other words, I want short if-statements on a single line but keep the {} around them) Currently I'm using the following configuration: AllowShortIfStatementsOnASingleLine: true AllowShortLoopsOnASingleLine: true AllowShortCaseLabelsOnASingleLine: true AllowShortFunctionsOnASingleLine: true...

## opencv window not refreshing at mouse callback

c++,opencv
I am trying to draw with mouse move in an opencv window. But when I draw, nothing draws on the window. When I try to close the window from the cross in the topleft(ubuntu), it opens a new window which it should be as I haven't pressed escape, and in...

## Reading all the files in sequence in MATLAB

matlab,image-processing
I am trying to read all the images in the folder in MATLAB using this code flst=dir(str_Expfold); But it shows me output like this. which is not the sequence as i want. Can anyone please tell me how can i read all of them in sequence? for giving downmark, please...

## C++ template template

c++,templates
I'm trying to understand C++ template templates by implementing a generic container class. Here is the code: using namespace std; template <typename T, template <typename STORETYPE> class Container> class Store { public: ~Store() {}; Store() {}; void someFunc( const T & ) {}; //... private: Container<T> storage; }; int main(int...

## Implicit use of initializer_list

c++,c++11,initializer-list
§[dcl.init.list] 8.5.4/2: The template std::initializer_list is not predefined; if the header <initializer_list> is not included prior to a use of std::initializer_list — even an implicit use in which the type is not named (7.1.6.4) — the program is ill-formed. Does that mean this program is ill-formed? #include <vector> int main()...

## C++11 Allocation Requirement on Strings

c++,string,c++11,memory,standards
I had heard that C++11 was going to require strings to be allocated in contiguous memory. I even thought I saw a stack overflow question on it, but I can't seem to find it. I know that in practice both gcc and Visual Studio do allocate strings contiguously, I'm just...

## Why are shaders and programs stored as integers in OpenGL?

I'm following the "OpenGL Superbible" book and I can't help but notice that when we create a shader and create the program that we attach the shaders to, we store them as GLuint which are unsigned integers. Why are they stored as numbers? What does the value of the number...

## Matlab — SVM — All Majority Class Predictions with Same Score and AUC = .50

matlab,svm,auc
I'm having a weird problem in training an SVM with an RBF kernel in Matlab. The issue is that, when doing a grid search, using 10-fold cross-validation, for the C and Sigma values I always get AUC values equal to approximately .50 (varying between .48 and .54 depending) -- I...

## dispatch response packet according to packet sequence id

c++,boost,boost-asio
I have a third-part server, and I'm writing a dll interface for it, my clients use my dll to communicate with the server. The protocol uses a long tcp connection, all traffic goes from this tcp connection. There could be sending/receiving multiple packets at the same time, like a send_msg...

## Explicit instantiation of class template not instantiating constructor

c++,templates,constructor,explicit-instantiation
I'm working on a project in C++ and am having trouble understanding what members of a template class get explicitly instantiated when I explicitly instantiate the template class. I've written the following file, which I then compile using Visual C++ 2008 Express Edition's Release configuration and then pop into a...

## Get an ordered list of files in a folder

c++,boost,boost-filesystem
I have used boost::filesystem::directory_iterator in order to get a list of all the available files into a given folder. The problem is that I supposed this method would give me the files in alphabetical order, while the results seem pretty random. Is there any fancy way of alphabetically sorting them?...

## function wait to execute

matlab,events,delay
In Matlab functions can be started at events,but occasionally, like with the resize function, the events are called in rapid order and the function is called many times in succession, which can cause weird behavior and lag. Is there a way to have it listen for the event but only...

python,c++,ctypes
I have a simple test function on C++: #include <stdio.h> #include <string.h> #include <stdlib.h> #include <locale.h> #include <wchar.h> char fun() { printf( "%i", 12 ); return 'y'; } compiling: gcc -o test.so -shared -fPIC test.cpp and using it in python with ctypes: from ctypes import cdll from ctypes import c_char_p...

## Incorrect Polar - Cartesian Coordinate Conversions. What does -0 Mean?

c++,polar-coordinates,cartesian-coordinates
I am getting incorrect conversions from polar to cartesian coordinates and vice versa. My code produces weird points like (1,-0). Im using this calculator to check my conversions. Also one of the conversions is completely wrong when I convert back to cartesian coordinates. Point b: (0,1) => (1,1.5708) => (0,0)...

## Checking value of deleted object

c++
I asked a question: Detecting if an object is still active or it has been destroyed Considering that I cannot use libraries, there are no good out of the box solutions in C++. So, is it a bad practice to check if the object has been destroyed by analyzing memory...

## Undefined behaviour or may be something with memset

c++,undefined-behavior
I was trying to save the binary equivalent of a 32 bit number in an array A. For testing my showbits() function , I choosed 8,9 when I came across this thing: I am facing an unreasonable thing in my code when I am placing memset in the function showbits(),I...

## Marshal struct in struct from c# to c++

c#,c++,marshalling
I have the following structures in C# and C++. C++: struct TestA { char* iu; }; struct TestB { int cycle1; int cycle2; }; struct MainStruct { TestA test; TestB test2; }; C#: [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Pack = 1)] internal struct TestA { [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 36)] private string iu; public...