How can I plot a new vector that have a relative length of another?

I have two points with coordinates in 3d space, and now I want to plot other vector with the same origin and with 30% of the length of the first one. For that I create a new ending point representing 30% of the coordinates of the 2nd point. This code work well if I have coordinates without decimal places, but in my data every coordinates have decimal places. Could you help me? Thanks. The code that I have is:

   p1=[70.025, 0.574, 0.370];
   p2=[140.590, -0.431, -0.226];
   x1=[p1(1) p2(1)];
   y1=[p1(2) p2(2)];
   z1=[p1(3) p2(3)];
   p3=[(p1(1)+p2(1)*0.3), (p1(2)+p2(2)*0.3), (p1(3)+p2(3)*0.3)];
   x2=[p1(1) p3(1)];
   y2=[p1(2) p3(2)];
   z2=[p1(3) p3(3)];
      hold on
      plot3(x1, y1, z1)
      plot3(x2, y2, z2, 'r')
      hold off

[Azzi Abdelmalek]

Why decimals are a problem?

[Marco Branco]

Thanks for your fast response. Because from my experiments with the code, I change the coordinates of the points to p1=[0, 0, 0]; p2=[10, -10, 10], and the plot became OK. I assume that decimal places make the propotion (of x,y and z coordinates) slight different. But it's just an opinion.

Answer 1

[Azzi Abdelmalek]

You can write

 p3=p1+0.3*p2

[Marco Branco]

I've tried with your suggestion and the result was the same i've got earlier.

[Azzi Abdelmalek]

Because

p3=p1+0.3*p2

%is not corresponding to your question, try

p3=p1+(p2-p1)*.3

[Marco Branco]

Perfect. Thanks.