New in version 2.2 is the ability to have the gas density variable as a power law in radius, i.e. , where and are the density and radius at the cloud illuminated face. NB Note that this creates the possibility for calculations which do not end. This because the citeria for a model to end are either that the input column density is reached, or that the electron fraction falls below xeemin. If radexp has a value -1 then the column density integral converges only logarithmically at best, and the specified column may never be reached. If radexp -2 the local ionization parameter will increase with radius, and so the gas will not recombine and the xeemin criterion will not be met.
New in version 221bn17 is a feature which allows an array of densities to be read in. It requires that the radexp input variable be set to a number more negative than -100. Then ordered pairs of (radius, density) are read in from a file called 'density.dat'. Reading continues until the end of the file is reached. The density and radius values override the values derived from the ordinary input parameters. But execution will stop if other ending criteria are satisfied, i.e. if the model column density exceeds the input value, or the electron fraction falls below the specified minimum. The code will stop with an error if the density.dat file does not exist, or if the radius values are not monotonically increasing.