Documentation of cosp

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Function Synopsis

prod=cosp(x,y,nya,minperc)

Help text

 function prod=cosp(x,y,nya,minperc)

 calculates area (cos) weighted projection of two map x and y 
 onto each other. 
 X and Y must be linemaps (going from NW to SE).
 
  NYA is the latidue axis of the maps (from top to bottom)
  MINPERC (opt) is the minimum percentage of points not missing for the whole
  procduct to be not missing (from 0 to 100).
  In a projection, the spatial mean is NOT removed from X and Y.
  However, the long term mean should be removed from each gridpoint.

Cross-Reference Information

Listing of function cosp

function prod=cosp(x,y,nya,minperc)

% make sure maps are 1 down, nulat*nulon across:
if size(x,2) == 1 ;x=x'; end
if size(y,2) == 1 ;y=y'; end
  
if nargin <4
  minperc=0;
else
  minperc=minperc/100;
end

if isempty(nya)
  error('Latitude axis has to be supplied')
end

nulat=length(nya);
nulon=length(x)/nulat;

w=cos(nya*pi/180);
w=w(:);

if size(x) == size(y) 
  else
    error ('X and Y are not the same size')
end

% wmat is a linemap that contains the weights
% for the data set.
weights=w(:,ones(1,nulon))';
weights=weights(:);
weights=weights';

minpoints=minperc*nulon*nulat;

use=~(isnan(x)|isnan(y));
nupoints=sum(use);
  if nupoints < minpoints
    prod=NaN;
  else
    prod=sum(weights(use).*y(use).*x(use))/(sum(weights(use)));
  end