Other Variables

  The following variables are also set in all drivers. Their usage is described in Chapter 2. In most cases, they do not need to be changed.

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• [lworkl] The size of the work array workl used by dnaupd. Must be set to at least 3*ncv*(ncv+6).
• [tol] The convergence criterion. The default setting is machine precision. However, the value of tol should be set to control the desired accuracy. Typically, the smaller this value the more work is required to satisfy the stopping criteria. However, setting this value too large may cause eigenvalues to be missed when there are multiple or clustered eigenvalues.    
• [ido] The reverse communication flag. Must be set to 0 before entering dsaupd.
• [bmat] Designates whether a standard (bmat = 'I') or generalized eigenvalue (bmat = 'G') problem
• [iparam(1)] The shifting strategy used during the implicitly restarted portion of an IRAM. Unless the user has an expert understanding of IRAM, an exact shifting strategy selected by setting iparam(1) = 1 should be used.
• [iparam(3)] Maximum number of IRAM iterations allowed.
• [iparam(7)] Indicates the algorithmic mode used with ARPACK.
• [rvec] Indicates whether eigenvectors are needed. If the eigenvectors are of interest, then rvec = .true. and set to .false. otherwise.