;+
; NAME:determ2
;
; PURPOSE: computes the determinant of n 2 by 2 arrays
;
; CATEGORY: no DO loops and better accuracy
;
; CALLING SEQUENCE: 2 cases:
;     res = determ2(z2ds)
;     res = determ2(z1d00,z1d01,z1d10,z1d11)
;
; INPUTS:
;     z2ds: an 2*2*n array
;     or
;     z1d00,z1d01,z1d10,z1d11: the four n elements arrays
;     defined as:
;              z2ds[0, 0, *] = z1d00
;              z2ds[0, 1, *] = z1d01
;              z2ds[1, 0, *] = z1d10
;              z2ds[1, 1, *] = z1d11
;
; OUTPUTS: n elements array, the determinent of each 2*2 arrrays
;
; EXAMPLE:
;
; a=findgen(2,2,5)
; print, determ2(a)
; FOR i=0,4 DO print, determ(a[*,*,i]) ; IDL solution
;
; MODIFICATION HISTORY:
;           S. Masson (smasson@lodyc.jussieu.fr)
;           July 11th, 2002
;-
FUNCTION determ2, a, b, c, d
;
  compile_opt idl2, strictarrsubs
;
  CASE n_params() OF
    1:res = a[0, 0, *]*a[1, 1, *]-a[0, 1, *]*a[1, 0, *]
    4:res = a[*]*d[*]-c[*]*b[*]
    ELSE:stop
  ENDCASE

  RETURN, res
END