Driver Types

Three types of driver routines  are provided for symmetric or Hermitian eigenproblems:

• a simple driver (name ending -EV) , which computes all the eigenvalues and (optionally) the eigenvectors of a symmetric or Hermitian matrix A;

• a divide and conquer driver (name ending -EVD) , which computes all the eigenvalues and (optionally) the eigenvectors of a symmetric or Hermitian matrix A using an algorithm based on divide and conquer ; the -EVD routines can be much faster than their -EV counterparts, but use more workspace;

• an expert driver (name ending -EVX) , which can compute either all or a selected subset of the eigenvalues, and (optionally) the corresponding eigenvectors.

Different driver routines are provided to take advantage of special structure or storage of the matrix A, as shown in Table 2.5.

In the future LAPACK will include routines based on the Jacobi algorithm [99][91][34], which are slower than the above routines but can be significantly more accurate.