@@ -6,10 +6,10 @@ This document provides the guide for using the *ELPA* library in user applicatio

Local documentation (via man pages) should be available (if *ELPA* has been installed with the documentation):

For example "man get_elpa_communicators" should provide the documentation for the *ELPA* function which sets

For example "man elpa_get_communicators" should provide the documentation for the *ELPA* function which sets

the necessary communicators.

Also a [online doxygen documentation] (http://elpa.mpcdf.mpg.de/html/Documentation/ELPA-2016.05.003/html/index.html)

Also a [online doxygen documentation] (http://elpa.mpcdf.mpg.de/html/Documentation/ELPA-2016.05.004/html/index.html)

for each *ELPA* release is available.

### General concept of the *ELPA* library ###

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@@ -20,14 +20,23 @@ The *ELPA* library consists of two main parts:

Both variants of the *ELPA* solvers are available for real or complex valued matrices.

Thus *ELPA* provides the following user functions (see man pages or [online] (http://elpa.mpcdf.mpg.de/html/Documentation/ELPA-2016.05.003/html/index.html) for details):

Thus *ELPA* provides the following user functions (see man pages or [online] (http://elpa.mpcdf.mpg.de/html/Documentation/ELPA-2016.05.004/html/index.html) for details):

-get_elpa_communicators : set the row / column communicators for *ELPA*

-elpa_get_communicators : set the row / column communicators for *ELPA*

- solve_evp_complex_1stage : solve a complex valued eigenvale proplem with the *ELPA 1stage* solver

- solve_evp_real_1stage : solve a real valued eigenvale proplem with the *ELPA 1stage* solver

- solve_evp_complex_2stage : solve a complex valued eigenvale proplem with the *ELPA 2stage* solver

- solve_evp_real_2stage : solve a real valued eigenvale proplem with the *ELPA 2stage* solver

*NEW*

- elpa_solve_evp_real : driver for *ELPA 1stage* or *ELPA 2stage* solver

- elpa_solve_evp_complex : driver for *ELPA 1stage* or *ELPA 2stage* solver

Furthermore *ELPA* provides the utility binary "print_available_elpa2_kernels": it tells the user

which *ELPA 2stage* compute kernels have been installed and which default kernels are set

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@@ -43,8 +52,8 @@ In this case, *ELPA* relies on a BLACS distributed matrix.

To solve a Eigenvalue problem of this matrix with *ELPA*, one has

1. to include the *ELPA* header (C case) or module (Fortran)

2. to create row and column MPI communicators for ELPA (with "get_elpa_communicators")

3. to call *ELPA 1stage* or *ELPA 2stage* for the matrix.

2. to create row and column MPI communicators for ELPA (with "elpa_get_communicators")

3. to call to the *ELPA driver* or directly call *ELPA 1stage* or *ELPA 2stage* for the matrix.

Here is a very simple MPI code snippet for using *ELPA 1stage*: For the definition of all variables

please have a look at the man pages and/or the online documentation (see above). A full version

With the definintions of the input and output variables:"

int na: global dimension of quadratic matrix a to solve

int nev: number of eigenvalues to be computed; the first nev eigenvalules are calculated

double *a: pointer to locally distributed part of the matrix a. The local dimensions are lda x matrixCols

int lda: leading dimension of locally distributed matrix a

double *ev: pointer to memory containing on output the first nev computed eigenvalues

double *q: pointer to memory containing on output the first nev computed eigenvectors

int ldq: leading dimension of matrix q which stores the eigenvectors

int nblk: blocksize of block cyclic distributin, must be the same in both directions

int matrixCols: number of columns of locally distributed matrices a and q

int mpi_comm_rows: communicator for communication in rows. Constructed with elpa_get_communicators

int mpi_comm_cols: communicator for communication in colums. Constructed with elpa_get_communicators

int mpi_comm_all: communicator for all processes in the processor set involved in ELPA

int THIS_ELPA_REAL_KERNEL: choose the compute kernel for 2-stage solver

int useQR: if set to 1 switch to QR-decomposition

char *method: use 1stage solver if "1stage", use 2stage solver if "2stage", (at the moment) use 2stage solver if "auto"

int success: return value indicating success (1) or failure (0)

DESCRIPTION

Solve the real eigenvalue problem. The value of method desides whether the 1stage or 2stage solver is used. The ELPA communicators mpi_comm_rows and mpi_comm_cols are obtained with the elpa_get_communicators function. The distributed quadratic marix a has global dimensions na x na, and a local size lda x matrixCols. The solver will compute the first nev eigenvalues, which will be stored on exit in ev. The eigenvectors corresponding to the eigenvalues will be stored in q. All memory of the arguments must be allocated outside the call to the solver.