Plot eigen Vector e1 & e2 in matlab?

How to be able plot eigen vector in Matlab an make it sure have the exact position as a new axes of our data??

here is my code for PCA

   a= randn(100,3); 
   b=mean(a);
   c=cov(a); 

   [vec,val] = eigs(c);
    e1=vec(:,1); 
    e2=vec(:,2); 

    plot3(a(:,1),a(:,2),a(:,3),'ro');
    hold on
    %%Here is the Problem begins
    plot(e1,'k--');
    plot(e2,'k--');

Here is the output that I got

That two lines represent the e1&e2 .

How to plot the e1 & e2 properly in 3D Vectors (plot3)???

Answer 1

[jandas]

The problem is that you try to plot the vector using 2D line plot so your script actually plots two lines in the XY plane through points {1, e1(1)}, {2, e1(2)}, {3, e1(3)} and {1, e2(1)}, {2, e2(2)}, {3, e2(3)}. If you need to plot a 3D vector you can plot it as a line between two points, e.g.:

plot3([0; e1(1)], [0; e1(2)], [0; e1(3)], 'k--');
plot3([0; e2(1)], [0; e2(2)], [0; e2(3)], 'k--');