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Nick Chepurniy, Ph.D.
HPC Consultant - SHARCNET
Compute Canada


Programs written in OCTAVE, LAPACK and ScaLAPACK are presented for obtaining the eigenvalues of non-symmetric matrices of a given size.


The objective of this online-tutorial is to present programs for obtaining the eigenvalues of non-symmetric matrices of a given size using OCTAVE, LAPACK and ScaLAPACK.

Some Definitions

We shall denote the order of the matrix A by N. Three packages will be used (OCTAVE, LAPACK and ScaLAPACK) to obtain the eigenvalues of matrix A. We will denote the size of the matrices as small, medium and large according to the following criteria: OCTAVE will be able to handle matrices of size up to "small", LAPACK will be able to handle matrices of size up to "medium' and ScaLAPACK will be able to handle matrices of size up to "large".

Preparing the Code

Preparing the code for these packages is very easy for OCTAVE, a bit more complicated for LAPACK and much harder for ScaLAPACK. To test the programs we pick the order of the matrix of size "small" which by definition can be run using all three packages. If all the elements of the matrix are real then we have a REAL non-symmetric matrix. If at least one elements is complex then the matrix is COMPLEX. The data type for a matrix will be denoted by the variable DATYPE: 'D' for real double precision matrices and 'Z' for complex double precision matrices.

For LAPACK and ScaLAPACK the programs: (1) obtain the upper Hessenberg form of matrix A, (2) use the Schur decomposition to obtain the eigenvalues. In OCTAVE the command: [U,S]=schur(A) computes the matrix S and the eigenvalues are obtained from the command: eigS = eig(S);

We shall define very simple non-symmetric matrices inside the programs and compare the eigenvalues obtained by the three packages.

The complete set of programs and scripts can be found in this tar file:

Eigenvalues and eigenvectors of Non-symmetric matrices (OCTAVE, LAPACK, ScaLAPACK)

See Eigenvalues and eigenvectors of Non-symmetric matrices (OCTAVE, LAPACK, ScaLAPACK)

You can copy above tar file into your /work/$USER directory on a cluster, say, narwhal, and untar the file by using the following commands:

cd /work/$USER/
tar -xvzf EIGEN.tar.gz

tar -xvzf NAG_LAPACK.tar.gz

In subdirectory NAG_LAPACK you will find script and source files for installing NAG's "extras" library. See

for instructions to install the "extras" library.

The EIGEN subdirectory has two subdirecrories:


The OCTAVE programs are in /work/$USER/EIGEN/OCTAVE and the LAPACK programs in /work/$USER/EIGEN/ZGEEV_EX.

The ScaLAPACK programs are in subdirectory /work/$USER/EIGEN


Let's start with the OCTAVE programs. Go to subdirecory OCTAVE and invoke octave and then execute "all" the OCTAVE commands in the file HIST. For example executing "gen08" (the first command in HIST) should produce the following output:

[nar316:/work/$USER/EIGEN/OCTAVE]  octave
GNU Octave, version 3.2.2
octave:1> gen0008
eps =  1.0000e-08
N =  8
All tests passed for eig_0008 ... generating file
trace_A =  8
sum_eigval =  8.0000
eps =  1.0000e-12
Sum eigenvalues = trace(A) criteria satisfied!

and the fourth command in the HIST file should produce:

octave:4>  Zgen0064
eps =  1.0000e-08
N =  64
All tests passed for Zeig_0064 ... generating file
trace_A =   0 + 64i
sum_eigval = -1.0202e-13 + 6.4000e+01i
eps =  1.0000e-12
Sum eigenvalues = trace(A) criteria satisfied!

The quit command will exit from octave and listing your files you should see four new files:


These are the files containing the eigenvalues for the four cases. Here the 'Z' and 'D' are the data type of the matrix A (described above) and 0064 and 0008 are the sizes of A.

Executing the script sort_eig_files by using command:


will produce files with the eigenvalues sorted:

[nar316:/work/nickc/EIGEN/OCTAVE]  ./sort_eig_files

Sorting the eigenvalues files ...

Sorted files:

We will compare these files with those generated by the other two programs once we generate similar files with LAPACK and ScaLAPACK.


To run the LAPACK jobs you require the "extras" libraries from NAG. This library should be placed in a subdirectory called lib under your home directory:

The LAPACK programs are in subdirectory:


The commands we need to execute are in the HIST file:

make clean




The "make clean" and "make" commands use the makefile "Makefile" to compile the LAPACK program that calculates the eigenvalues for matrix A which is defined to be identical to the A in the OCTAVE subdirectory.

The script "./run_4_cases" is used to submit the jobs to the test queue. We have executed the jobs interactively, since they are very short. These four jobs produce four files containing the eigenvalues:


The next script "./sort_eig_files" sorts above files and places the corresponding sorted eigenvalues into:


Then the final script in HIST, "./compare_LAPACK_2_OCTAVE", compares the sorted eigenvalues generated by OCTAVE and LAPACK for each of the four cases. You should see the following:

[nar316:/work/nickc/EIGEN/ZGEEV_EX] ./compare_LAPACK_2_OCTAVE

Comparing Zeig_0008
No DIFFERENCES detected for Zeig_0008

Comparing Zeig_0064
No DIFFERENCES detected for Zeig_0064

Comparing Deig_0008
No DIFFERENCES detected for Deig_0008

Comparing Deig_0064
No DIFFERENCES detected for Deig_0064


So far we have been using a set of matrices of size 8 or 64 with commands in HIST. A second set of matrices of sizes 800 and 880 can be found in HIST2. Of course you can copy HIST or HIST2 into HIST3 and make the appropriate changes in HIST3 and copy all other files referenced by HIST3 commands and do the required changes to run different cases. Note that there is no need to have four cases per HIST file, you can have any munber of cases.

For ScaLAPACK jobs we must use the scripts in the HIST file in subdirectory:


Here is the HIST file for ScaLAPACK:


        vi pznepdriver.f
        vi pznepinfo.f


        rm -rf *.o

        make clean



#  Above script submits jobs into the regular queue


# Sort eigenvalues in the files


# Compare results



If the system is busy and the regular jobs (i.e. those not going though the
test queue) are taking a long time your jobs might run faster if you use
scripts that submit jobs to the test queue:





However, since you can have only one job in the test queue you must wait
until the job in the test queue finishes before you submit the next job
to the test queue.

# Sort eigenvalues in the files


# Compare results


The final script in HIST, ./compare_ScaLAPACK_2_OCTAVE, compares the eigenvalues generated by OCTAVE and ScaLAPACK for each of the four cases in HIST2:

[nar316:/work/nickc/EIGEN]   ./compare_ScaLAPACK_2_OCTAVE_2

Comparing Zeig_0800
No DIFFERENCES detected for Zeig_0800

Comparing Zeig_0880
No DIFFERENCES detected for Zeig_0880

Comparing Deig_0800
No DIFFERENCES detected for Deig_0800

Comparing Deig_0880
No DIFFERENCES detected for Deig_0880

Running a new set of problems

To run a new set of problems calculating eigenvalues:

(1) Copy the HIST file into a NEW_HIST file, say HIST3

(2) In HIST3 append "_3" to the three scripts, i.e.

    ./sub_all_4                   becomes   ./sub_all_4_2
    ./sort_eig_files              becomes   ./sort_eig_files_2
    ./compare_ScaLAPACK_2_OCTAVE  becomes   ./compare_ScaLAPACK_2_OCTAVE_2

(3) Create the new scripts by copying them from those in HIST, i.e.

    cp ./sub_all_4                    ./sub_all_4_2
    cp ./sort_eig_files               ./sort_eig_files_2
    cp ./compare_ScaLAPACK_2_OCTAVE   ./compare_ScaLAPACK_2_OCTAVE_2

(4) Edit the new scripts.

   (A) In ./sub_all_4_2 specify the new NEP.dat_Xnnnn file
       where X is either X of D and nnnn is the size of the matrix

       Then create the new NEP.dat_Xnnnn files by copying those in HIST
       into the new name, e.g.

            cp NEP.dat_D0008   NEP.dat_D0950

       then edit NEP.dat_D0950 and enter the correct values.

(5) Run the ./sub_all_4_3 script  and read the OUTPUT statements.
    You will probably need to edit programs and
    recompile it using the "make" command see HIST3 file.

(6) Edit ./sort_eig_files_3 and run this script

(7) Edit ./compare_ScaLAPACK_2_OCTAVE_3 and run this script

Eigenvalues and Eigenvectors

The program PZGEEV can be used to get the eigenvalues and eigenvectors of a non-symmetric matrix.

Last update: 12 Sept 2013