# Long Runtimes

Long runtimes occur when the frequency grid and/or spatial grid contain many points. The execution time to process a single &mode namelist group can be approximated by

$\tau \approx C_{\rm b} N M + C_{\rm s} N N_{j},$

where $$N$$ is the number of spatial points, $$M$$ is the number of frequency points, $$N_{j}$$ is the number of modes found, and $$C_{\rm b}$$ and $$C_{\rm s}$$ are constants. The first ($$C_{\rm b}$$) term represents the time take to bracket roots of the discriminant function, and the second ($$C_{\rm s}$$) the time taken to solve for these roots (see the GYRE Fundamentals chapter for details).

The key to ensuring reasonable runtimes lies in judicious choice of parameters in the &scan namelist group(s). The n_freq parameter obviously has an impact on $$\tau$$, as it directly sets $$M$$. However, the freq_min and freq_max parameters also influence $$\tau$$, due to the way the spatial grid is constructed. If the frequency scan includes parts of the star’s oscillation spectrum containing modes with very large radial orders (whether p modes or g modes), then GYRE’s iterative refinement algorithm will insert many grid points in order to resolve the modes’ wavefunctions. This can ultimately lead to huge $$N$$ and very long runtimes.