R/human-SIS-dts.R
    dts_lines_X_SIS_dts.RdAdd lines for the density of infected individuals for the SIS_dts model
dts_lines_X_SIS_dts(XH, nStrata, clrs = c("darkblue", "darkred"), llty = 1)a list with the outputs of parse_dts_out_X_SIS_dts
the number of population strata
a vector of colors
an integer (or integers) to set the lty for plotting