Advantages of using external libraries Many times, you may find it useful and convenient to install softwares which have been developed and written by others. In this way, you can simply focus more on writing kernel parts of your main algorithms, leaving others to write the rest of numerical subroutines for you. Examples of such routines may vary depending on your needs, but in general, some of the popular choices are numerical linear algebra, I/O, parallel load distributions, mesh generations, etc. This approach not only saves your efforts and time, but also keeps your kernal algorithms computationally efficient and compatible on various platforms as long as the external libraries are continuosly supported and maintained. About BLAS and LAPACK In this section we learn how to install external software packages. We are going to search for them, compile them to produce libraries, include and link those libraries to compile with your Fortran subroutines. Two most popular examples of external libraries, especially for scientific computing, are the (Basic Linear Algebra Subroutines) and (Linear Algebra PACKage) packages. They are both freely-available softwares which allow users to call various linear algebra subroutines in their programs. Hi, I hope this is the right place to post my question. I am trying to run a program which needs the LAPACK/BLAS library. I have been able to set up the library but when I try to run my program I get this error. This is the make.inc when I first install lapack: FORTRAN = ifort OPTS = -O3 DRVOPTS = $(OPTS) NOOPT = -O3 -fltconsistency -fp. The BLAS package is originally a reference Fortran library. It is a collection of basic linear algebra routines that are standard buidling blocks for basic vector and matrix operations. With this reason, many numerical software packages (including LAPACK, LINPACK, OCTAVE, MATLAB, Mathematica, NumPy, and R) adopts the BLAS and develop their linear algebra softwares as BLAS-compatible libraries. LAPACK is an improved version of LINPACK, which provides a standard numerical linear algebra routines using the BLAS library as a buidling block implementation. That is to say, routines in LAPACK perform computations by calling the routines of the BLAS. With BLAS and LAPACK, you can call from your routines to perform mathematical operations in numerical linear algebra such as (see also ). $ cd /usr/lib/ $ ls -all $. $ liblapack.dylib ->././System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libLAPACK.dylib The -> means that the default provided library file liblapack.dylib in /usr/lib/ is a to the file called /libLAPACK.dylib in the location. To further check if you have the BLAS and LAPACK properly installed already, go to lectureNote/chapters/chapt02/codes/lapack/linear and compile solve1.f90 using the LAPACK library flag -llapack (basically you can check out this flag by compiling any Fortran code which doesn’t even call any LAPACK routines ). #################################################################### # LAPACK make include file. # # LAPACK, Version 3.7.1 # # June 2017 # #################################################################### SHELL = /bin/sh # CC is the C compiler, normally invoked with options CFLAGS. # CC = gcc CFLAGS = -O3 # Modify the FORTRAN and OPTS definitions to refer to the compiler # and desired compiler options for your machine. ![]() ![]() NOOPT refers to # the compiler options desired when NO OPTIMIZATION is selected. # # Note: During a regular execution, LAPACK might create NaN and Inf # and handle these quantities appropriately. As a consequence, one # should not compile LAPACK with flags such as -ffpe-trap=overflow. # FORTRAN = gfortran OPTS = -O2 -frecursive DRVOPTS = $(OPTS ) NOOPT = -O0 -frecursive # Define LOADER and LOADOPTS to refer to the loader and desired # load options for your machine. # LOADER = gfortran LOADOPTS = # The archiver and the flag(s) to use when building an archive # (library). If your system has no ranlib, set RANLIB = echo. Note As just mentioned, the correct way to link a static library (i.e., *.a files) is using -l, but that only works if the library can be found on the search path, say, in your.bashrc or.bash_profile. If it’s not the case, however, you need to add -L flags followed by the directory path, in the makefile if you’ve put libraries in nonstandard places. On the other hand, if you’re interested in linking a shared library (i.e., *.so files), you define an environment variable, LD_LIBRARY_PATH which include the directory paths to the target shared library (see more ). Also see an article on their differences.
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