# 3rd Order Polynomial Not Through the Origin

summary:

When the input does not go straight through the origin, the behavior of the polynomial becomes hard to guess in both the animations and complex planes.

description:

The yellow line is the input that goes through the origin for red, a cubic polynomial with real coefficients. The blue line is an input that does not go through the origin, making the curved orange line. That curve appears to line in a plane defined by the yellow and blue lines. The shape of the orange line is distinct from that of the red line. What goes in can dramatically change what comes out. The sharp bend in the t-x graph for the orange line was unexpected.

command:
q_graph -out poly_3_off_diagonal -dir poly -box 5 -command 'q_add_n -3 -3 -3 -3 .006 .005 .004 .003 1000 | q_poly -n 3 -c 1 -n 1 -c 3 -n 0 -c -2' -color orange -command 'q_add_n -3 -3 -3 -3 .005 .005 .005 .005 1000 | q_poly -n 3 -c 1 -n 1 -c 3 -n 0 -c -2' -color red -command 'q_add_n -3 -3 -3 -3 .005 .005 .005 .005 1000' -color yellow
math
equation:

Input for red: (-3, -3, -3, -3) to (2, 2, 2, 2)
Input for orange: (-3, -3, -3, -3) to (3, 2, 1, 0)
Output for red and orange: $q^3 + 3 q - 2$

tags
Math Tag:
polynomials
Programming Tag:
command line quaternions