Hold Position Once Condition Is Met

I am moving points within a for loop. However, once a point reaches a specific position, I would like it to hold that position. How can I do this?

[Rik]

That depends on how you are moving the points.

[Allison Bushman]

P1=[-11,0];
    P2=[-1,0];
    h{1}=plot([P1(1) P2(1)],[P1(2) P2(2)],'LineWidth',5,'Color','black');

    A=[0,0];
    h{3} = viscircles(A,1,'LineWidth',2,'Color','black'); 
    PA=A+[cos(a(k)-(pi)),sin(a(k)-(pi))];
    h{4}=viscircles(PA,.1,'Color','black');
    
    B =A+[2*cos(a(k)-x),2*sin(a(k)-x)];
    if 2*cos(a(k)-x)>=0 && 2*sin(a(k)-x)>=0
        B=[2,0];
    end
    h{5} = viscircles(B,1,'LineWidth',2,'Color','green');
    PB=B+[cos(a(k)-(pi/2)),sin(a(k)-(pi/2))];
    h{6}=viscircles(PB,.1,'Color','green');
    
    C = B+[2*cos(a(k)-y),2*sin(a(k)-y)];
    if (2*cos(a(k)-x)+2*cos(a(k)-y))>0 && (2*sin(a(k)-x)+2*sin(a(k)-y))>0
        C=[4,0];
    end
    h{7} = viscircles(C,1,'LineWidth',2,'Color','blue');
    PC=C+[cos(a(k)-y),sin(a(k)-y)];
    h{8}=viscircles(PC,.1,'Color','blue');

[Allison Bushman]

This is a snippet of the code. I am trying to get B to hold at the point (2,0) and C at (4,0)

[Star Strider]

a = ?

[Allison Bushman]

0:pi/40:pi