angle-betw​een-a-vect​or-and-the​-positive-​x-axis

How can i find an angel between x axis and vector

[fi,ro]=cart2pol(X-X(1),Y-Y(1)-20); [fim1,id]=max(fi); Rom1=ro(id); [xm1,ym1]=pol2cart(fim1,rom1); Xm1=X(1)+[0,xm1]; Ym1=Y(1)+20+[0,ym1];

Answer 1

[Bjorn Gustavsson]

Have a look at the help for atan2.

HTH

[Maria Tipikina]

I have read it yet. I can't find angle

[Bjorn Gustavsson]

You simply call atan2:

phi = atan2(Ycomponent,Xcomponent);

And there you have your angle between the vector and the x-axis, in radians.

Or more explicitly to calculate the angles for 8 vectors, try this exqample:

plot([1 1 0 -1 -1 -1 0 1]',[0 1 1 1 0 -1 -1 -1]','s-'),axis([-1 1 -1 1]*1.1)
arrow(0*[[0 1 1 1 0 -1 -1 -1]',[1 1 0 -1 -1 -1 0 1]'],[[0 1 1 1 0 -1 -1 -1]',[1 1 0 -1 -1 -1 0 1]'])
atan2([0 1 1 1 0 -1 -1 -1]',[1 1 0 -1 -1 -1 0 1]')*180/pi

(The arrow function you'll have to download from the file exchange.)

HTH