MATLAB Answers

increasing values midway of an array for theta (using atan2();)

4 views (last 30 days)
Michal Sleszynski
Michal Sleszynski on 6 Feb 2020
Edited: Michal Sleszynski on 6 Feb 2020
Im wondering if this is an atan2 problem #if so how can i fix it# . I have values of theta that are decreasing and then they start to increase and so the polarplot im producing shows a spiral that turns around at some point. You can view the arrays in the txt files attached . All variables/arrays are of the size 1x101.
Thank you in advance.
theta = atan2(r,t);
theta = theta*360;
rho = sqrt((t.^2)+(r.^2));
figure
polarplot(theta,rho,'b')

Answers (1)

Steven Lord
Steven Lord on 6 Feb 2020
Remember is that atan2 returns values in the closed interval [-pi, pi] so if you go from a y that is just barely positive to one that is just barely negative and x is negative, you'll experience that "sudden drop". The unwrap function may be useful to you in that scenario.
By the way, if you wanted to have theta in degrees that's not the right conversion. You should use atan2d instead. But polarplot expects its theta input to be in radians, so maybe just eliminate the multiplication by 360.
  2 Comments
Michal Sleszynski
Michal Sleszynski on 6 Feb 2020
unwrap didnt work on my theta i di change the conversion a bit , the result being equivilent to what i get by using *360
theta = atan2(r,t);
theta = 2*pi*(theta)*180/pi;
theta = unwrap(theta);

Sign in to comment.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by