Utility function to compute the inverse of a Circulant matrix.
If A is circulant, its inverse also is circulant.
  Arguments
      
    
      
        | Type | Intent | Optional | Attributes |  | Name |  | 
    
        
            | type(Circulant), | intent(in) |  |  | :: | A | Input matrix. | 
    
  
    
    Return Value
    type(Circulant)
    
    Inverse of A.