If t is a scalar, result is a scalar double precision scale factor. If t is an array, result is a double precision array with the scale factors for each t value.
calc_scale might also return -1000 in some cases. The reason for this is the following. If the function is called for a specific t value (and other parameters), it is not obvious in advance if this time value is further in the past than the age of the universe (determined by the parameters). If it is further in the past than the age of the universe, -1000 is returned. If result is used for further calculation, it should be truncated to get rid of these bad values. If it only used for plots, the y plot range may be set strating with 0, which then automatically suppresses the bad values. For information about how to deal with this see section IVD below.