; docformat = 'rst'
;+
;Component magnitude of vector u in the direction of vector b.
;
; :Examples: 
;   component_magnitude = comp(vector_u, vector_b)
;-
;+
; :Params:
;   u : in, required, type=vector of int or vector of double
;     Input vector to compute the component magnitude from.
;   b : in, required, type=vector of int or vector of double
;     Input vector that gives the direction for the component 
;     magnitude.
;     
; :Returns:
;   Returns the component magnitude of vector u in the direction
;   of vector b. 
;-
function comp,u,b
  if (n_elements(u) eq 0 or n_elements(b) eq 0) then begin
    doc_library, 'comp'
    return, -1
  endif
  return,dotp(u,b)/vlength(b)
end