Return the parameters
to make sharkfin function for an bednet round.
     
    
    Usage
    make_bednet_profile(d_50, d_shape, start_day, peak, length = 20, pw = 1)
 
     
    
    Arguments
- d_50
 
the day when efficacy reaches 50%
 
- d_shape
 
the decay shape
 
- start_day
 
the start day for the bednet round
 
- peak
 
the maximum value
 
- length
 
the number of days it took to complete spraying
 
- pw
 
a shape parameter
 
 
    
    Value
    a sharkfin function object