Modify other variables if necessary

  The following variables are also set in all drivers. Their usage is described in Chapters 2 and 3. In most cases, they do not need to be changed.

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• [lworkl] Must be set to at least ncv*ncv+3*ncv.
• [tol] Usually set to zero. It can be changed depending on the accuracy desired. 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 they are multiple or very tightly clustered.    
• [ido] Must be set to 0 before entering dnaupd.
• [info] Usually set to 0. In this case, a random starting vector is generated to start the Arnoldi iteration. If the user decides to use other starting vector, this value should be set to 1, and the starting vector should be provided in the array resid.
• [bmat] Either 'I' or 'G' depending on the problem to be solved. This variable has been set appropriately in each driver. The user should not change its value.
• [iparam(1)] Usually set to 1. This indicates that exact shift strategy is used in the computation. For a discussion on shift strategy see  4.4.1 of Chapter  4.
• [iparam(3)] Maximum iterations allow. It is set to 300 in all drivers. But it can be reset to any reasonable value.
• [iparam(7)] Indicate algorithmic mode. This variable has been set appropriately in each driver. The user should not change its value.
• [rvec] Indicate whether eigenvector is needed. It is set to .true. in all drivers. If no eigenvector is needed, this may be set to .false.