Why won't my line functions display their lines?

This function takes in x-, y- and z-coordinates of a plane from X, Y, and Z. Then it imports the coordinates of a cube (centered over the origin) and is supposed to plot a parallel projection of the cube onto the plane (using the point on the plane that I calculate here).

I can't figure out why my line functions at the end won't work, when the ones I use for my drawCuboid() function work just fine.

      function drawParProjCuboid(X,Y,Z)
        %draw parallel projection of cuboid on oblique plane
        %figure;
        hold on;

        %plane points are within X, Y, & Z

        %Get cube points
        fid=fopen('inFileCub.txt','r');
        R=fscanf(fid,'%f');
        for i=1:24
           if i>=1 && i<=8
               x(i)=R(i);
           end
           if i>=9 && i<=16
               y(i-8)=R(i);
           end
           if i>=17 && i<=24
               z(i-16)=R(i);
           end
        end
        CP1=[x(1);y(1);z(1)];
        CP2=[x(2);y(2);z(2)];
        CP3=[x(3);y(3);z(3)];
        CP4=[x(4);y(4);z(4)];
        CP5=[x(5);y(5);z(5)];
        CP6=[x(6);y(6);z(6)];
        CP7=[x(7);y(7);z(7)];
        CP8=[x(8);y(8);z(8)];

        %(x-x1)/l = (y-y1)/m = (z-z1)/n
        %find point on plane: (x1,y1,z1)
        x1=(X(1)-2); y1=(Y(1)-2);

        Ax=X(1); Ay=Y(1); Az=Z(1);
        Bx=X(2); By=Y(2); Bz=Z(2);
        Cx=X(3); Cy=Y(3); Cz=Z(3);

        z1a = (Bx-Ax)*(Cz-Az)-(Cx-Ax)*(Bz-Az);
        z1b = (Bx-Ax)*(Cy-Ay)-(Cx-Ax)*(By-Ay);
        z1c = (By-Ay)*(Cz-Az)-(Cy-Ay)*(Bz-Az);
        z1d = (Bx-Ax)*(Cy-Ay)-(Cx-Ax)*(By-Ay);

        z1 = Az+(y-Ay)*z1a/z1b-(x-Ax)*z1c/z1d;

        %z1=Az+(((Bx-Ax)(Cz-Az)-(Cx-Ax)(Bz-Az))/((Bx-Ax)(Cy-Ay)-(Cx-Ax)(By-Ay)))(y1-Ay)-...
        %    (((By-Ay)(Cz-Az)-(Cy-Ay)(Bz-Az))/((Bx-Ax)(Cy-Ay)-(Cx-Ax)(By-Ay)))(x1-Ax);

        %direction vector
        d=[(x1-CP1(1)),(y1-CP1(2)),(z1-CP1(3))];

        % This plane's equation:
        % t = (x-CP1(1))/d(1) = (y-CP1(2))/d(2) = (z-CP1(3))/d(3)

        % PP#(x) = (y1-CP#(2))d(1)/d(2)
        % PP#(y) = (z1-CP#(3))d(2)/d(3)
        % PP#(z) = (x1-CP#(1))d(3)/d(1)

        %Find all parallel-projected point values:
        XP=[(d(1)*(y1-CP1(2))/d(2)),(d(1)*(y1-CP2(2))/d(2)),(d(1)*(y1-CP3(2))/d(2)),...
            (d(1)*(y1-CP4(2))/d(2)),(d(1)*(y1-CP5(2))/d(2)),(d(1)*(y1-CP6(2))/d(2)),...
            (d(1)*(y1-CP7(2))/d(2)),(d(1)*(y1-CP8(2))/d(2))];
        YP=[(d(2)*(z1-CP1(3))/d(3)),(d(2)*(z1-CP2(3))/d(3)),(d(2)*(z1-CP3(3))/d(3)),...
            (d(2)*(z1-CP4(3))/d(3)),(d(2)*(z1-CP5(3))/d(3)),(d(2)*(z1-CP6(3))/d(3)),...
            (d(2)*(z1-CP7(3))/d(3)),(d(2)*(z1-CP8(3))/d(3))];
        ZP=[(d(3)*(x1-CP1(1))/d(1)),(d(3)*(x1-CP2(1))/d(1)),(d(3)*(x1-CP3(1))/d(1)),...
            (d(3)*(x1-CP4(1))/d(1)),(d(3)*(x1-CP5(1))/d(1)),(d(3)*(x1-CP6(1))/d(1)),...
            (d(3)*(x1-CP7(1))/d(1)),(d(3)*(x1-CP8(1))/d(1))];
        figure;
        line([XP(1) XP(5)],[YP(1) YP(5)],[ZP(1) ZP(5)],'color','m');
        line([XP(1) XP(2)],[YP(1) YP(2)],[ZP(1) ZP(2)],'color','m');
        line([XP(1) XP(4)],[YP(1) YP(4)],[ZP(1) ZP(4)],'color','m');
        line([XP(7) XP(6)],[YP(7) YP(6)],[ZP(7) ZP(6)],'color','m');
        line([XP(7) XP(8)],[YP(7) YP(8)],[ZP(7) ZP(8)],'color','m');
        line([XP(7) XP(3)],[YP(7) YP(3)],[ZP(7) ZP(3)],'color','m');
        line([XP(5) XP(6)],[YP(5) YP(6)],[ZP(5) ZP(6)],'color','m');
        line([XP(5) XP(8)],[YP(5) YP(8)],[ZP(5) ZP(8)],'color','m');
        line([XP(4) XP(3)],[YP(4) YP(3)],[ZP(4) ZP(3)],'color','m');
        line([XP(4) XP(8)],[YP(4) YP(8)],[ZP(4) ZP(8)],'color','m');
        line([XP(2) XP(3)],[YP(2) YP(3)],[ZP(2) ZP(3)],'color','m');
        line([XP(2) XP(6)],[YP(2) YP(6)],[ZP(2) ZP(6)],'color','m');

        end

[Walter Roberson]

Check for nan and inf in the coordinates.