#NEWLINE# def compute_timestep( self ) : #NEWLINE# #INDENT# '\n        The diffusion timestep() function computes the timestep\n        using the explicit timestep constraint as the starting point.\n        We then multiply by the CFL number to get the timestep.\n        Since we are doing an implicit discretization, we do not\n        require CFL < 1.\n        ' #NEWLINE# cfl = self . rp . get_param ( 'driver.cfl' ) #NEWLINE# k = self . rp . get_param ( 'diffusion.k' ) #NEWLINE# xtmp = ( ( self . cc_data . grid . dx ** 2 ) / k ) #NEWLINE# ytmp = ( ( self . cc_data . grid . dy ** 2 ) / k ) #NEWLINE# self . dt = ( cfl * min ( xtmp , ytmp ) )