The edge model is absorption edge, given by.

1 

where:
par1= 
threshold energy 
par2 
absorption depth at the threshold 
The zedge model given by

1 E < E_{c} 
E > E_{c} 
allows a redshift z where:
par1 = E_{c} 
threshold energy 
par2= D 
absorption depth at threshold 
par3= z 
redshift 