% 計算有限長載流導體段AB在空間場點C處產生的磁感應強度
%  [B]= b_cal(Start_point,End_point,Destination_piont,CurrentValue)   
%     輸入參數：
%       Start_point : 線段起點A的坐標，單位：m； 
%       End_point:  線段終點B的坐標，單位：m；
%       Destination_piont: 場點C的坐標，單位：m；
%       CurrentValue: 線段中的電流強度，單位：A；
%     返回參數：
%       B: 場點C處磁感應強度的三個分量 [Bx, By,Bz], 單位：T
%     注意事項：
%       場點不能放置在載流線段或者載流段的延長線上。
%     
%     例子：
%       Start_point = [0 0 0]; %       End_point = [1 1 1]; %       Destination_piont = [7 8 9];
%       CurrentValue = 1;     
%
%       [B]= b_cal(Start_point,End_point,Destination_piont,CurrentValue)   
% 
    
function  [B]= b_cal(Start_point,End_point,Destination_piont,CurrentValue)   

	DestinationX=Destination_piont(1);
	DestinationY=Destination_piont(2);
	DestinationZ=Destination_piont(3);

    StartX=Start_point(1);
    StartY=Start_point(2);
    StartZ=Start_point(3);
    
    
    EndX=End_point(1);
    EndY=End_point(2);
    EndZ=End_point(3);
    
	    U	=	4 * pi*1E-7;
        SCALARCO	=	U/4/pi;
		
        Bx=0;
        By=0;
        Bz=0;
		
			Delta_2	=sqrt((DestinationX-StartX)^2+(DestinationY...
     				 -StartY)^2+(DestinationZ-StartZ)^2);
			Delta_3	=sqrt((DestinationX-EndX)^2+(DestinationY...
     			     -EndY)^2+(DestinationZ-EndZ)^2);
		

			Arfa_x	=(EndY-StartY)*(DestinationZ-StartZ)-...
     				(EndZ-StartZ)*(DestinationY-StartY);

			Arfa_y	=(EndZ-StartZ)*(DestinationX-StartX)-...
     				 (EndX-StartX)*(DestinationZ-StartZ);

			Arfa_z	=(EndX-StartX)*(DestinationY-StartY)-...
     				 (EndY-StartY)*(DestinationX-StartX);

     
					
			R_Equvillent=Arfa_x^2 + Arfa_y^2+Arfa_z^2;

			L_Source=(EndX-StartX)^2+(EndY-StartY)^2+(EndZ-StartZ)^2;
			                    

			sinArfa1_Up	=(DestinationX-StartX)*(EndX-StartX)+...
						 (DestinationY-StartY)*(EndY-StartY)+...
    					 (DestinationZ-StartZ)*(EndZ-StartZ);

			sinArfa2_Up	=(DestinationX-EndX)*(EndX-StartX)+...
     					 (DestinationY-EndY)*(EndY-StartY)+...
               		     (DestinationZ-EndZ)*(EndZ-StartZ);

	
			
			sinArfa1=sinArfa1_Up/Delta_2;
			sinArfa2=sinArfa2_Up/Delta_3;				
		
			magB=(sinArfa1-sinArfa2)/R_Equvillent;
			BX=magB*Arfa_x;
			BY=magB*Arfa_y;
			BZ=magB*Arfa_z;
	
		

		    BX=SCALARCO* CurrentValue * BX;
		    BY=SCALARCO* CurrentValue * BY;	
		    BZ=SCALARCO* CurrentValue * BZ;	
			
            B=[BX BY BZ];