; docformat = 'rst'
;+
;This function takes in a vector and returns its length. The vector must be 
;3-Dimensional. 
;
; :Examples:
;   vector_length = vlength(vector)
;-
;+
; :Params:
;   v : in, required, type=vector of int or vector of double
;     Input vector that must be 3-dimensional.
;     
; :Returns: 
;   Returns the length of the input vector.
;-
function vlength,v
  if n_elements(v) eq 0 then begin
    doc_library, 'vlength'
    return, -1
  endif
  resolve_grid,v,x=x,y=y,z=z
  lensq=x^2+y^2+z^2;
  len=sqrt(lensq);
  return,len;
end