elpa_eigenvalues_double(3)

💅 elpa_eigenvalues_double — the elpa_eigenvalues_double(3) page, bestie edition

okay so this is a page from the Library Functions Manual and honestly? it's a bop. it's giving "find all the eigenvalues of a real symmetric problem" and we're gonna walk through it together, no gatekeeping 💖

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✨ NAME ✨

elpa_eigenvalues_double — computes, like, all the eigenvalues λ for a real symmetric eigenproblem:

A*Q = λ*Q

that's the whole vibe. main character energy fr fr 🌸

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🫶 SYNOPSIS 🫶

🌈 FORTRAN INTERFACE

use elpa
class(elpa_t), pointer :: elpa_handle

call elpa_handle%eigenvalues_double (a, ev, error)

and here's the definitions of the input and output variables, because i would never leave you guessing 💅

• class(elpa_t) :: elpa_handle — an instance of the ELPA object. your handle. your little ELPA bestie.
• real(kind=c_double) :: a OR type(c_ptr) :: a — the local part of the host/device matrix A for which the eigenvalues should be computed. 🚨 the dimensions of matrix a must be set BEFORE with the methods elpa_set(3) and elpa_setup(3). also! the global matrix has to be symmetric, and this is not checked by the routine — so that's on you, not on ELPA 😭. in case of a GPU build a can be a pointer to the device memory.
• real(kind=c_double) :: ev OR type(c_ptr) :: ev — the global array where the eigenvalues λ will be stored, in ascending order. ⭐ in case of a GPU build ev can be a pointer to the device memory.
• integer, optional :: error — the return error code of the function. should be "ELPA_OK". the error code can be queried with the function elpa_strerr(3) 🔍

🦋 C/C++ INTERFACE

#include <elpa/elpa.h>
elpa_t elpa_handle;

void elpa_eigenvalues_double(elpa_t elpa_handle, double *a, double *ev,
int *error);

and with the definitions of the input and output variables, icons only ✨

• elpa_t elpa_handle; — the handle to the ELPA object.
• double *a; — the local part of the host/device matrix A for which the eigenvalues should be computed. again, for the people in the back 📢: the dimensions of matrix a must be set BEFORE with the methods elpa_set(3) and elpa_setup(3). the global matrix A has to be symmetric, and this is not checked by the routine. in case of a GPU build a can be a pointer to the device memory.
• datatype_real *ev; — the array where the eigenvalues λ will be stored in ascending order. and yes, eigenvalues will be stored in ascending order. we said it twice because it matters 💜. in case of a GPU build ev can be a pointer to the device memory.
• int *error; — the error code of the function. should be "ELPA_OK". the error codes can be queried with elpa_strerr(3).

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🔥 DESCRIPTION 🔥

computes the eigenvalues of a double precision real symmetric matrix. that's the whole job, and it ate 💅

⚠️ the functions elpa_init(3), elpa_allocate(3), elpa_set(3), and elpa_setup(3) must be called BEFORE elpa_eigenvalues_double can be called. like, non-negotiable. do the prep work first, bestie. no skipping steps 😤

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👑 SEE ALSO 👑

your reading list, go off 📚✨

elpa2_print_kernels(1) · elpa_init(3) · elpa_allocate(3) · elpa_set(3) · elpa_setup(3) · elpa_strerr(3) · elpa_skew_eigenvalues(3) · elpa_eigenvectors(3) · elpa_skew_eigenvectors(3) · elpa_cholesky(3) · elpa_invert_triangular(3) · elpa_solve_tridiagonal(3) · elpa_eigenvalues(3) · elpa_uninit(3) · elpa_deallocate(3)

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and that's the page!! this one's brought to you by ELPA, dated Thu Nov 28 2024 — so go call elpa_init(3) first, mwah, talk later 🫶💖✨