function a = RBF1learn( x, y, mu, sigma )

%function a = RBF1learn( x, y, mu )
% learn RBF parameter 'a_j' by LMS
%  with fixed  mu, sigma

[d,T] = size( y );  % d; target vector dimension, T; number of data
[q,T] = size( x );  % q; data vector dimension
[q,M] = size( mu ); % M; number of base centers
a = zeros( d, M );

  % デフォルトでは y(t) の次元 d = 1 であるから、
  % 以下で':'とあるところは、省略しても可。

K = zeros( M, M );
z = zeros( d, M );
for t = 1:T
  for j = 1:M
    x_mu = x(:,t) - mu(:,j);
    k(j) = exp( -x_mu'*x_mu/(2*sigma^2) );
    z(:,j) = z(:,j) + k(j)*y(:,t);
  end
  K = K + k'*k;
end
z = z/T;
K = K/T;
for n = 1:d
  a(n,:) = z(n,:)*inv(K); 
end