GPU accelerated vessel segmentation using Laplacian eigenmaps

NOTE
    The codebase has not been maintained since June 2014. Use it with your own
    risk. **Note that it does not work with MAGMA version 1.5.0 or later. Please
    use MAGMA version 1.4.1**.

SYNOPSIS
    Laplacian eigenmap is an image segmentation algorithm that began to gain
    traction in recent years. It involves a generalized eigenvalue problem
    which extracts high-level features from local neighborhood information.
    Unfortunately, it is computationally costly to compute eigenvalues of a
    large linear systems. We make use of general-purpose GPUs to accelerate the
    segmentation process.

DOCUMENTATION
    See https://hyunsu-cho.io/eigenmap_gpu.html.

DEPENDENCIES
    1. MAT file I/O Library              --> See Step 1 of HOW TO COMPILE
       http://matio.sourceforge.net/

    2. MAGMA (Matrix Algebra on GPU and Multicore Architectures)
       http://icl.cs.utk.edu/magma/index.html
       **Make sure to use MAGMA version 1.4.1**.

    3. ATLAS (Automatically Tuned Linear Algebra Software)
       http://math-atlas.sourceforge.net/

HOW TO COMPILE
    1. Run ./get_matio.sh to automatically download and install the MAT file
       I/O Library. This library is required to read and write in MATLAB's
       binary MAT file format.
    
    2. Open the Makefile and edit the system paths (lines 13-16) as necessary.

    3. Run make.

HOW TO RUN
    To make things easier, we rely on MATLAB's image processing facilities when
    it comes to pre-/post-processing. Hence, do the following steps:

    1. Put the input image in Test_Data directory. The image must have jpg
       extension.

    2. Launch MATLAB in graphical mode.
    
    3. Run one of the bootstrap scripts with the name of the image. Each script
       has a suffix that represents a distinct scenario:

       - bootstrap_c(...)   : compute Laplacian eigenmap using one CPU thread
       - bootstrap_omp(...) : use many CPU threads
       - bootstrap_gpu(...) : use one GPU device instead
       - bootstrap_vanilla(...) : use one CPU thread; really slow because the
         entire script is written in MATLAB's scripting language

       To get an intuitive feeling of how the bootstrap scripts look like, take
       a quick look at  test.m.

       More precisely, bootstrap calls share the following form:

       bootstrap_x('image_name', [param1], [param2], [# of Lanczos iterations]) 
    
       For instance, if the input image is example.jpg, the parameters are 10
       and 50, and the number of Lanczos iterations is 75, use:

       bootstrap_x('example', 10, 50, 75);

    4. The segmented images pop up as figures and at the same time are saved in
       results directory.

FUNCTION SUMMARY
    -  pairweight: computes the weight matrix.
    -  laplacian:  computes the Laplacian matrix from the weight matrix.
    -  eigs:       computes a few smallest eigenvalues of the Laplacian matrix;
                   uses general symmetric eigenvalue solver.
    -  lanczos:    computes a few smallest eigenvalues of the Laplacian matrix;
                   uses the Lanczos method.