If t is scalar, magt returns a scalar floating point magnitude for the given stretch, redshift and cosmology. If t is an array, magt returns a floating point array with the magnitudes for each of the values in the array t. If the distance modulus calculation with calc_dm resulted in an error because the given cosmological parameters describe a bouncing universe, magt prints an error message and returns -1000. For more information on calc_dm visit
http://panisse.lbl.gov/groupwork/documentation/cosmo/index.html
If for the given filter and redshift no K correction was possible (see section 3.3.1 below), magt returns -1000 and prints an error message.