Time

Gabrielle Allen

Date

Abstract

Calculates the timestep used for an evolution

1 Purpose

This thorn provides routines for calculating the timestep for an evolution based on the spatial Cartesian grid spacing and a wave speed.

2 Description

Thorn Time uses one of four methods to decide on the timestep to be used for the simulation. The method is chosen using the keyword parameter time::timestep_method.

In all cases, Thorn Time sets the Cactus variable cctk_delta_time which is passed as part of the macro CCTK_ARGUMENTS to thorns called by the scheduler.

Note that for hyperbolic problems, the Courant condition gives a minimum requirement for stability, namely that the numerical domain of dependency must encompass the physical domain of dependency, or

Δt min(Δxi)wave speedd im

3 Examples

Fixed Value Timestep

time::timestep_method = "given"  
time::timestep        = 0.1

Calculate Static Timestep Based on Grid Spacings

The following parameters set the timestep to be 0.25