Example: Consider the linear system
Find the matrix coefficient of the system. Then, discuss the fate of the long term behavior of the solutions. If they go to infinity, discuss how.
Answer: The matrix coefficient of the system is
Note that if you have the wrong matrix coefficient the conclusion
about the solutions may totally differ from the right answer!
In order to find the general solution we need the characteristic equation
Its roots are given by the quadratic formulas
which gives or . Next, we need to find the associated eigenvectors.
The two equations lead to the same equation . If we choose , we get
The second equation is worthless and the first one implies . If we choose , we get
where and are two parameters.
We know that since the system has one positive eigenvalue the solutions will tend to infinity as t goes to . We also know that the solutions will get closer and closer to the straight-line solution which corresponds to the biggest eigenvalues. In this case, the line generated by the vector
is clearly the x-axis. See the graph below.
Do you need more help? Please post your question on our S.O.S. Mathematics CyberBoard.
Author: Mohamed Amine Khamsi