;---------------------------------------------
; 22 Oct 2014
; in respose to an ncl-talk question:
; Hopefully the following is helpful.  It returns both partial and 
; part correlations, but if you want you can ask for only one of them 
; to be returned using the optional argument "opt"
;
; e.g opt=True
;     opt@partialcorrelation=True
; Saji Hameed saji.nh@gmail.com
;-------------------

function mreg_part_corr(x1,x2,y,opt)
local opt
begin
  x1x2 = escorc(x1,x2)
  tol = sqrt(1-x1x2^2)

  nx1 = dimsizes(x1)
  X = new( (/3,nx1/), float)
  X(0,:) = 1.0
  X(1,:) = x1
  X(2,:) = x2

  beta = reg_multlin(y, X, False)
  dreg = beta(1)
  nreg = beta(2)

  Xstd = dim_stddev(X)
  Ystd = stddev(y)
  XstdYstd = Xstd/Ystd
  B = beta*XstdYstd
  B(0) = 0.0
  part_corr_x1 = B(1)*tol
  part_corr_x2 = B(2)*tol
  partial_corr_x1 = part_corr_x1/sqrt((1-(escorc(y,x2))^2))
  partial_corr_x2 = part_corr_x2/sqrt((1-(escorc(y,x1))^2))
  if opt .and. isatt(opt,"part_correlation")
    if opt@part_correlation
    return((/part_corr_x1, part_corr_x2/))
    end if 
end if
  if opt .and. isatt(opt,"partal_correlation")
    if opt@partial_correlation
      return((/partial_corr_x1, partial_corr_x2/))
    end if
  end if
  res=(/partial_corr_x1,partial_corr_x2,part_corr_x1,part_corr_x2/)
  return(res)
end