Calculate eigenvalue eigenvector in fortran

• Comp Sci
• baha_tr
baha_tr
Homework Statement
Hello, I used to use Fortran 70 before and now I started using Fortran 2023, but I think the library usage is a little different. I wonder how we connect the libraries in 2023, I would be happy if you can help me.
Relevant Equations
intel fortran 2023
I wonder how we connect the libraries in 2023

There is no 'the' libraries, there are many many libraries, what do you want? You can use e.g. LAPACK to compute eigenvalues.

pbuk and FactChecker
I just need to find the 4 states after the base state, I think I will use lapack or dsyevx.

Calling a Fortran 77 library from Fortran 2023 should be straightforward. Calling it as you would if you wrote your program in Fortran 77 should work.

"Intel MKL ERROR: Parameter 9 was incorrect on entry to DSYEVX". I am getting error code like this

ı have solved my problem

What is an eigenvalue and eigenvector?

An eigenvalue is a scalar that indicates how much the eigenvector is stretched during a linear transformation. An eigenvector is a non-zero vector that only changes by the scalar factor (the eigenvalue) when a linear transformation is applied to it.

How do I calculate eigenvalues and eigenvectors in Fortran?

In Fortran, you can use built-in libraries such as LAPACK (Linear Algebra PACKage) to calculate eigenvalues and eigenvectors. LAPACK provides routines like DSYEV for symmetric matrices, which can be called from Fortran code to perform these calculations.

What libraries are available in Fortran for eigenvalue and eigenvector computation?

The most commonly used library for eigenvalue and eigenvector computation in Fortran is LAPACK. LAPACK provides a comprehensive suite of routines for linear algebra operations, including eigenvalue and eigenvector calculations for various types of matrices.

Can you provide a simple example of Fortran code to find eigenvalues and eigenvectors?

Sure! Here is a basic example using LAPACK:

program eigen_example    implicit none    integer :: n, lda, info, lwork    double precision, allocatable :: a(:,:), w(:), work(:)        ! Define matrix size and allocate arrays    n = 3    lda = n    lwork = 3*n    allocate(a(n,n), w(n), work(lwork))        ! Initialize matrix 'a'    a = reshape([4.0d0, 1.0d0, -2.0d0, 1.0d0, 2.0d0, 0.0d0, -2.0d0, 0.0d0, 3.0d0], shape(a))        ! Call LAPACK routine to compute eigenvalues and eigenvectors    call dsyev('V', 'U', n, a, lda, w, work, lwork, info)        ! Check for successful execution    if (info == 0) then        print *, 'Eigenvalues: ', w        print *, 'Eigenvectors: ', a    else        print *, 'Error: LAPACK dsyev routine failed with info = ', info    end if        ! Deallocate arrays    deallocate(a, w, work)end program eigen_example
This program initializes a 3x3 matrix, computes its eigenvalues and eigenvectors using the LAPACK routine DSYEV, and prints the results.

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