How to make Armadillo work on Windows? - c++

Question

I cannot make Armadillo 4.3 work on Windows. The library armadillo/include is included and I run g++ "-LC:\\Armadillo\\BLAS_Lapack" -o1 -o test.exe test.o -llapack -lblas, then I get the following error message:
C:/Armadillo/include/armadillo_bits/blas_wrapper.hpp:183: undefined reference to `wrapper_ddot_'
test.o: In function `ZN4arma4blas4gemvIdEEvPKcPKiS5_PKT_S8_S5_S8_S5_S8_PS6_S5_':
C:/Armadillo/include/armadillo_bits/blas_wrapper.hpp:34: undefined reference to `wrapper_dgemv_'
test.o: In function `ZN4arma4blas4gemmIdEEvPKcS3_PKiS5_S5_PKT_S8_S5_S8_S5_S8_PS6_S5_':
C:/Armadillo/include/armadillo_bits/blas_wrapper.hpp:69: undefined reference to `wrapper_dgemm_'
If I run g++ -o1 -o test.exe test.o -llapack -lblas, I get
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -llapack
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -lblas
I did uncomment the configuration file config.hpp according to the README file.
Does anybody know how to make Armadillo work? (I am using Eclipse CDT.)

Answer 1

It took a while to get this right, but it seems transparent once it works. I will explain step by step. (Make sure you have uncommented the correct lines as directed in the README of the config.hpp file)
The general command for compiling with blas/lapack (using the default provided with armadillo (current version 4.500.0) and does make it faster :)
g++ main.cpp -I C:{ARMADILLO_ROOT}\include -L C:{ARMADILLO_ROOT}\examples\lib_win64 -lblas_win64_MT -llapack_win64_MT
where each of the commands are as follows:
g++: GNU G++ Compiler (using MinGW 4.9.1 C++ from equationsolution.com)
main.cpp: My main file of the C++ program (I have an abstract and concrete class defining the Levenshtein algorithm)
-I C:{ARMADILLO_ROOT}\include: The GCC C++ Compiler Include Path (To include the Armadillo library) where ARMADILLO_ROOT is where you have decompressed and placed your armadillo files
-L C:{ARMADILLO_ROOT}\examples\lib_win64: The MinGW C++ Linker Library Link Path (To link the BLAS and LAPACK libraries) I have used the default libs provided with armadillo, I believe and according to the doc you may and should substitute these linear libraries in a production instance)
-lblas_win64_MT -llapack_win64_MT: Identify the libraries to be used (name must match, so you cannot put -lblas or -llapack UNLESS your files are named that way - by default in this armadillo version they are named blas_win64_MT lapack_win64_MT (win64 since I am using both a MinGW/C++ 64bit and a 64bit armadillo [they should match])
Following this logic, you may configure eclipse (using eclipse Luna R1 4.4.1 -should be the same procedure on other versions) with the following:
Right Click the Project and Select "Properties" item in the popup menu
Under "C/C++ Build" on the left menu Select "Settings"
Under "GCC C++ Compiler" click on "Includes (-I)" and add the include path C:{ARMADILLO_ROOT}\include (Screenshot1)
Under "MinGW C++ Linker" click on "Libraries" add each "Libraries (-l)" as named blas_win64_MT lapack_win64_MT. (Screenshot2)
Under the same "MinGW C++ Linker" click on "Libraries" add a "Library search path (-L)" C:{ARMADILLO_ROOT}\examples\lib_win64
Click the "Apply" button before pressing "OK"
--Screenshot1
--Screenshot2

Answer 2

It seems to work now! I am using the Lapack and BLAS from the webpage indicated in the Readme file that I compiled myself according to #enhzflep comments.
To link everything properly in Eclipse CDT right click on your project and go to properties, then:
Under "C/C++ Build⟼Settings⟼GCC C++ Compiler⟼Command" type: g++ -I"C:\Armadillo\include" (replace with the correct path for your Armadillo folder). Make sure to do this for all Configurations (to be chosen in the drop-down menu at the top).
Under "C/C++ Build⟼Settings⟼MinGW C++ Linker⟼Libraries" add lapack and blas to the Libraries.
Under"C/C++ General⟼Paths and Symbols⟼GNU C++" add the path tot he include directory of your Armadillo folder C:\Armadillo\include.
It might be that it works with the original Lapack and BLAS files. It did not work for me, because I had only added the path to Armadillo under "C/C++ General⟼Paths and Symbols⟼GNU C++", which I guess only tells the editor what data types and functions to expect and not the compiler.

Answer 3

If you're using MinGW on Windows, a good option is to use OpenBLAS with Armadillo. OpenBLAS provides optimized and multi-threaded implementations of BLAS and LAPACK:
http://xianyi.github.io/OpenBLAS/
The OpenBLAS project provides pre-compiled versions for Windows. The source code can be also easily compiled under Linux and MacOS X.
Note that Armadillo doesn't support automatic installation under Windows. The cmake based installer provides a big fat warning message about that -- you're advised to heed it.
Instead of automatic installation, do the following (as described in the README.txt file that comes with Armadillo):
Manually modify include/armadillo_bits/config.hpp to enable the use of BLAS and LAPACK. In other words, make sure that ARMA_USE_BLAS and ARMA_USE_LAPACK are uncommented (enabled).
Also within include/armadillo_bits/config.hpp, disable ARMA_USE_WRAPPER, ie. make sure it's commented out.
When compiling your C++ programs, tell your compiler to use the armadillo include folder directly, and link with openblas. For example, with gcc use the -I switch to specify the include folder.