High-Performance Computing (HPC) relies heavily on optimized linear algebra libraries like LAPACK and BLAS for efficient numerical computations. When setting up an HPC environment, or encountering errors during execution, a common problem is the inability to locate these crucial libraries. This guide will walk you through troubleshooting where LAPACK and BLAS are located on your system, common reasons for them not being found, and solutions to resolve these issues.
What are LAPACK and BLAS?
Before diving into troubleshooting, let's briefly clarify what LAPACK and BLAS are:
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BLAS (Basic Linear Algebra Subprograms): This is a fundamental library providing low-level routines for vector and matrix operations. It forms the foundation for many higher-level linear algebra libraries.
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LAPACK (Linear Algebra PACKage): Built upon BLAS, LAPACK provides a wider range of higher-level routines for solving linear equations, eigenvalue problems, and singular value decompositions. It's a crucial component for many scientific and engineering applications.
Where are LAPACK/BLAS located on my system?
The location of LAPACK and BLAS libraries varies significantly depending on your operating system, HPC software stack (e.g., Intel MKL, OpenBLAS, ACML), and installation method. Here's a systematic approach to finding them:
1. Using the ldconfig command (Linux):
On Linux systems, the ldconfig command is your friend. It manages the dynamic linker's cache, containing information about shared libraries. Open your terminal and execute the following:
ldconfig -p | grep -i blas
ldconfig -p | grep -i lapack
This command will list all shared libraries containing "blas" or "lapack" in their names, along with their paths. This is usually the most effective way to locate these libraries.
2. Checking common installation directories:
If ldconfig doesn't reveal the location, manually check common directories where libraries are often installed:
- /usr/lib/
- /usr/local/lib/
- /lib/
- /opt/<package_name>/lib/ (replace
<package_name>with the name of your HPC package, e.g., intel-mkl) - /usr/lib64/ (for 64-bit systems)
Use the find command to search recursively within these directories:
find /usr/lib -name "*liblapack*" 2>/dev/null
find /usr/lib -name "*libblas*" 2>/dev/null
The 2>/dev/null part suppresses error messages for directories you don't have access to.
3. Examining your compiler's environment:
Your compiler (e.g., g++, icc) might have environment variables pointing to the location of libraries it uses. Check variables like:
LIBRARY_PATHLD_LIBRARY_PATHINCLUDE
You can use echo $LIBRARY_PATH or similar commands to check their values.
4. Checking your HPC software's documentation:
Consult the documentation for your specific HPC software (e.g., Intel MKL, OpenBLAS, etc.). This will provide precise instructions for locating the libraries within the software's installation directory.
Why can't I find LAPACK/BLAS? Common Reasons & Solutions
Several reasons could explain why you're unable to find LAPACK/BLAS:
1. Libraries not installed:
Solution: Install the necessary libraries using your system's package manager (e.g., apt, yum, pacman) or by compiling them from source. If using a pre-built HPC suite, ensure it's properly installed and configured.
2. Incorrect environment variables:
Solution: Correctly set your LD_LIBRARY_PATH or LIBRARY_PATH environment variables to include the directory containing the LAPACK/BLAS libraries. Remember that these changes might require restarting your terminal or logging out and back in.
3. Compiler/linker issues:
Solution: Verify that your compiler is configured correctly and can find the necessary libraries during compilation and linking. This may involve specifying library paths using compiler flags like -L (for library paths) and -l (for library names, e.g., -llapack, -lblas).
4. Conflicting library versions:
Solution: Ensure you don't have multiple conflicting versions of LAPACK/BLAS installed. Remove older or unnecessary versions to avoid conflicts.
5. Incorrect module loading (HPC clusters):
On HPC clusters, you often need to load specific software modules before using libraries. Use the module avail and module load commands to ensure the correct modules (e.g., Intel MKL, OpenBLAS) are loaded before compiling or running your code.
Using the right flags during compilation
Remember to use the correct compiler flags to link against LAPACK and BLAS. For example:
g++ -llapack -lblas myprogram.cpp -o myprogram
By systematically following these steps, you'll be able to pinpoint the location of your LAPACK/BLAS libraries and resolve any issues preventing their use in your HPC applications. Remember to consult the documentation for your specific system and software for the most accurate and up-to-date information.
