How can I draw vectors in octave?

Question

I want to make a program that adds two vectors and plots them together with their addition. But they have to be position vectors.

I tried creating v1=[0;2] and v2=[1;3] but displaying them with plot results in a number of scattered points.

How can I specify the starting position of the vectors, eg make v1 and v2 start from the origin?

Answer 1

I usually do what you are describing with the quiver function, whose purpose is to draw vector fields. Your example could be drawn with

   xx=[0;2];
   yy=[0;0];
   quiver(xx,yy,[0;1],[2;3],0,"linewidth",4);axis equal;xlim([-4 4]);ylim([0 5]);grid on;

It produces the following output:

The starting points of the vectors are specified by the two variables xx and yy in the following way: the starting point of the n-th vector is given by [xx(n,1);yy(n,1)] (look at help meshgrid for information on that. Basically, meshgrids are just a way to define the domain of a function, which here happens to be a vector field).

Answer 2

Here is an example of drawing math vectors in Octave:

clf
xs=[0 0 1 5 0]
ys=[0 0 7 1 0]
xe=[5 1 5 1 6]
ye=[1 7 1 7 8]
q=1;
h=quiver(xs(q),ys(q),xe(q),ye(q), 0,'b');
hold on
set (h, "maxheadsize", 0.033);
q=3;
h=quiver(xs(q),ys(q),xe(q),ye(q), 0,'--b');
set (h, "maxheadsize", 0.033);
q=2;
h=quiver(xs(q),ys(q),xe(q),ye(q), 0,'r');
set (h, "maxheadsize", 0.033);
q=4;
h=quiver(xs(q),ys(q),xe(q),ye(q), 0,'--r');
set (h, "maxheadsize", 0.033);
q=5;
h=quiver(xs(q),ys(q),xe(q),ye(q), 0,'g');
set (h, "maxheadsize", 0.033);
axis("square")
grid on
hold off