Off, chaos. On, it stands up.
Four numbers hold a pole upright while the gusts grow. One of them points the way nobody expects.
Play →A score is a cost, in the units the system lives in, and lower is better. The textbook plays in the same world, next to you; the world changes at midnight; every plant hides something its manual left out. Runs stay in your browser.
Every linear system responds as a sum of modes shaped like est. The numbers s are its poles; left of the imaginary axis they decay, on it they ring, to the right they grow. Feedback is the art of moving poles into the left half-plane, cheaply, and keeping them there when the world turns out to differ from the model. The card, with the picture.