function  [r, dr] = correxpg(theta, d)%CORREXPG  General exponential correlation function%%           n%   r_i = prod exp(-theta_j * d_ij^theta_n+1)%          j=1%% If n > 1 and length(theta) = 2, then the model is isotropic: % theta_j = theta(1), j=1,...,n;  theta_(n+1) = theta(2) %% Call:    r = correxpg(theta, d)%          [r, dr] = correxpg(theta, d)%% theta :  parameters in the correlation function% d     :  m*n matrix with differences between given data points% r     :  correlation% dr    :  m*n matrix with the Jacobian of r at x. It is%          assumed that x is given implicitly by d(i,:) = x - S(i,:), %          where S(i,:) is the i'th design site. % hbn@imm.dtu.dk  % Last update April 12, 2002[m n] = size(d);  % number of differences and dimension of datalt = length(theta);if  n > 1 & lt == 2  theta = [repmat(theta(1),1,n)  theta(2)];elseif  lt ~= n+1  error(sprintf('Length of theta must be 2 or %d',n+1))else  theta = theta(:).';endpow = theta(end);   tt = repmat(-theta(1:n), m, 1);td = abs(d).^pow .* tt;r = exp(sum(td,2));if  nargout > 1  dr = pow  * tt .* sign(d) .* (abs(d) .^ (pow-1)) .* repmat(r,1,n);end