vb_dipole_mag

 Dipole magnetic field 
  B0 = vb_dipole_mag(J0,x0,X,Q)
 双極子磁場計算
 x0 の双極子 J0 が 観測点 X に作る磁場の Q 方向射影
 B0 = Q*(JJ x Xd)/|Xd|^3 , Xd = X - x0

 2004-02-06 Taku Yoshioka
 2004-12-26 M. Sato modified

 Copyright (C) 2011, ATR All Rights Reserved.
 License : New BSD License(see VBMEG_LICENSE.txt)

0001 function    B0 = vb_dipole_mag(J0,x0,X,Q)
0002 % Dipole magnetic field
0003 %  B0 = vb_dipole_mag(J0,x0,X,Q)
0004 % 双極子磁場計算
0005 % x0 の双極子 J0 が 観測点 X に作る磁場の Q 方向射影
0006 % B0 = Q*(JJ x Xd)/|Xd|^3 , Xd = X - x0
0007 %
0008 % 2004-02-06 Taku Yoshioka
0009 % 2004-12-26 M. Sato modified
0010 %
0011 % Copyright (C) 2011, ATR All Rights Reserved.
0012 % License : New BSD License(see VBMEG_LICENSE.txt)
0013   
0014 Xd = [X(:,1)-x0(1), X(:,2)-x0(2), X(:,3)-x0(3)];
0015 dd = sum( Xd.^2, 2 );
0016 Rx = sqrt(dd).*dd;
0017     
0018 % 外積計算 JJ x Xd
0019 JB = [J0(2).*Xd(:,3) - J0(3).*Xd(:,2), ...
0020       J0(3).*Xd(:,1) - J0(1).*Xd(:,3), ...
0021       J0(1).*Xd(:,2) - J0(2).*Xd(:,1)];
0022     
0023 B0 = sum( JB.*Q, 2 )./Rx;