SURRGT3B.DOG

function yrev = surrgt3b(x,y,yr,yrc);
% surrgt3b:  surrogate series for assigned surrogates; no overlap version
% CALL: yrev = surrgt3b(x,y,yr,yrc);
%
% Meko 4-20-97
%
%************************ IN 
%
% x (mx x 1)r  predictor series (surrogate series)
% y (my x 1)r  predictand series (series needing data)
% yr (myr x 1)i   year vector, applies to x and y
% yrc (myrc x 1)i  year vector for calibtation period
%
%
%*************************** OUT
%
% yrev (mx x 1)r revised for of y, with NaN data in calibration
%  period replaced with 'standardized anomaly' estimates
%
%*************************** NOTES **********************
%
% x has complete data for calibration period.  y has some
% or all data NaN in calibration period.  Objective is to
% replace the calibration period NaN of y with estimates from
% x.  Estimates are such that standardized anomalies from 
% the long-term mean are the same for the missing-data period
% for series x and y.


[mx,nx]=size(x);
[my,ny]=size(y);

if nx~=1 | ny~=1;
   error('col size of x, y should be 1');
end
if mx~=mx;
   error('x and y should have same row size');
end
if length(yr) ~= length(x)
   error('yr must be same length as x, y');
end

% Initialize yrev as y
yrev=y;

% Year settings
yrgo=yr(1);
yrsp=yr(mx);

yrcgo=yrc(1);
yrcsp = yrc(length(yrc));

% Pointers to rows of x and y
L1=yr>=yrcgo & yr<=yrcsp; % calibration period
L2=isnan(y); % NaN data in y
L3=L1 & L2; % NaN data in calibration period in y

% Long term means and std devs of x and y
xmean=nanmean(x);
ymean=nanmean(y);
xstd=nanstd(x);
ystd=nanstd(y);

% Stdzd anomalies of x from its long term mean
x1= (x-xmean)/xstd;

% Synthetic y based on stdzd anomalies of x
y1 = ymean + x1*ystd;

% Replace calibration period NaNs in yrev with synthetic y
yrev(L3)=y1(L3);