function [res] = alge_odr_hook (what, x, b);%ALGE_ODR_HOOK%       %       Function called by odr, %       wants either 'f' or 'df'%%       See also ODR.  xc = x(:,1) - b(1)*ones(size(x,1),1);  yc = x(:,2) - b(2)*ones(size(x,1),1);  if     (strcmp(what, 'f')),    res = b(3)*xc.^2 + 2*b(4)*xc.*yc + b(5)*yc.^2 - ones(size(x,1),1);  elseif (strcmp(what, 'df')),    res = zeros(size(x,1),7);    res(:,6) = 2*b(3)*xc + 2*b(4)*yc;    res(:,7) = 2*b(5)*yc + 2*b(4)*xc;    res(:,1) = -res(:,6);    res(:,2) = -res(:,7);    res(:,3) = xc.^2;    res(:,4) = 2*xc.*yc;    res(:,5) = yc.^2;  else    str = sprintf ('unknown command: %s', what);    error (str);  endend % alge_odr_hook