Sum two mrs_data objects.
     
    
    sum_mrs(a, b, force = FALSE)
 
     
    
    Arguments
- a
 
first mrs_data object to be summed.
 
- b
 
second mrs_data object to be summed.
 
- force
 
set to TRUE to force mrs_data objects to be summed, even if they
are in different time/frequency domains.