Memory usage of st wslda

Arithmetics

Static codes support two types of arithmetics:

• double complex: ELEMENT_SIZE=16B
  default mode: matrix elements of hamiltonian are assumed to be of complex numbers.
• double: ELEMENT_SIZE=8B
  if you know that matrix elements, as well as the solution, will be real numbers (for examples based on symmetries of your problem) you can speed-up the calculation process by switching to double arithmetics. To do this you need to activate in predefines.h flag:

/**
 * activate this if you know that Hamiltonian matrix is real, 
 * the code will utilize it in order to speed-up the calculations
 * */
#define MATRIX_IS_REAL

st-wslda-3d

3D version of the code diagonalizes matrix of size:
MATRIX_DIM = NX*NY*NZ*2.
Memory needed store this matrix in memory is
MATRIX_SIZE = MATRIX_DIM*MATRIX_DIM*ELEMENT_SIZE.
To execute diagonalization routine st-wslda-3d code needs at most:
REQUIRED_MEMORY < 4*MATRIX_SIZE,
Factor 4 accounts for storage for matrix, storage for eigen-vectors, working space which depends on selected [diagonalization engine](Setting up diagonalization engine) and execution parameters.

st-wslda-2d

In (quasi) 2D formulation of the problem diagonalization of full hamiltonian matrix factorizes into a series of max(NZ/2,1) diagonalizations of matrices of size (NZ/2 arises from fact that there is the degeneracy of states with respect to sign of $k_z$ wave-vectors):
MATRIX_DIM = NX*NY*2
and the corresponding matrix size is
MATRIX_SIZE = MATRIX_DIM*MATRIX_DIM*ELEMENT_SIZE.
Number of matrices diagonalized simultaneously is:
NUMBER_OF_SIMULTANUES_DIAGONALIZATIONS = np / (p*q)
where np is number of MPI processes (provided to mpi execution command) and p and q are input file parameters. To execute diagonalization routine st-wslda-2d code needs at most:
REQUIRED_MEMORY < 4*MATRIX_SIZE*NUMBER_OF_SIMULTANUES_DIAGONALIZATIONS.

Note: if p and q are not specified in the input file, by default st-wslda-2d will select the values that provide the highest parallelization (maximization of a number of simultaneous diagonalization). It means the highest memory request.

st-wslda-1d

In (quasi) 1D formulation of the problem diagonalization of full hamiltonian matrix factorizes into a series of max(NY*NZ/4,1) diagonalizations of matrices of size:
MATRIX_DIM = NX*2
and the corresponding matrix size is
MATRIX_SIZE = MATRIX_DIM*MATRIX_DIM*ELEMENT_SIZE.
Number of matrices diagonalized simultaneously is:
NUMBER_OF_SIMULTANUES_DIAGONALIZATIONS = np / (p*q)
where np is number of MPI processes (provided to mpi execution command) and p and q are input file parameters. To execute diagonalization routine st-wslda-1d code needs at most:
REQUIRED_MEMORY < 4*MATRIX_SIZE*NUMBER_OF_SIMULTANUES_DIAGONALIZATIONS.

Note: if p and q are not specified in the input file, by default st-wslda-1d will select the values that provide the highest parallelization (maximization of a number of simultaneous diagonalization). It means the highest memory request.