Determine the nature of the origin (attractor, repeller, or saddle point) for the dynamical system \({{\rm{x}}_{k + 1}} = A{{\rm{x}}_k}\) if A has the properties described in Exercise 2. Find the directions of greatest attraction or repulsion.

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Short Answer

Expert verified

The direction of greatest repulsion is the line through the origin and the eigenvector\((1,0, - 3)\), and \(( - 3,3,7)\).

Step by step solution

01

Find eigenvalue and eigenvector 

Consider the dynamic system

\({{\rm{x}}_{k + 1}} = A{{\rm{x}}_k}\)

Where A is \(3 \times 3\) a matrix with eigenvalue \(3,\frac{4}{5}\;{\rm{and}}\;\frac{3}{5}\).

And eigenvectors are \({{\rm{v}}_1} = \left( {\begin{aligned}{}1\\0\\{ - 3}\end{aligned}} \right),{{\rm{v}}_2} = \left( {\begin{aligned}{}2\\1\\{ - 5}\end{aligned}} \right)\) and \({{\rm{v}}_3} = \left( {\begin{aligned}{}{ - 2}\\{ - 5}\\3\end{aligned}} \right)\).

Here, one of the Eigenvalue 3 is greater than 1 in magnitude and an Eigenvalues are \(\frac{4}{5}\;{\rm{and}}\;\frac{3}{5}\) less than 1 in magnitude, therefore origin is a saddle point for the dynamical system.

02

Find the direction 

The direction of greatest repulsion is the line through the origin and the eigenvector\((1,0, - 3)\), for the eigenvalue 3.

The direction of greatest attraction is the line through the origin and the eigenvector \(( - 3,3,7)\), for the smallest eigenvalue \(\frac{3}{5}\).

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Most popular questions from this chapter

Question: Is \(\left( {\begin{array}{*{20}{c}}4\\{ - 3}\\1\end{array}} \right)\) an eigenvector of \(\left( {\begin{array}{*{20}{c}}3&7&9\\{ - 4}&{ - 5}&1\\2&4&4\end{array}} \right)\)? If so, find the eigenvalue.

If \(p\left( t \right) = {c_0} + {c_1}t + {c_2}{t^2} + ...... + {c_n}{t^n}\), define \(p\left( A \right)\) to be the matrix formed by replacing each power of \(t\) in \(p\left( t \right)\)by the corresponding power of \(A\) (with \({A^0} = I\) ). That is,

\(p\left( t \right) = {c_0} + {c_1}I + {c_2}{I^2} + ...... + {c_n}{I^n}\)

Show that if \(\lambda \) is an eigenvalue of A, then one eigenvalue of \(p\left( A \right)\) is\(p\left( \lambda \right)\).

Define\(T:{{\rm P}_3} \to {\mathbb{R}^4}\)by\(T\left( {\bf{p}} \right) = \left( {\begin{aligned}{{\bf{p}}\left( { - 3} \right)}\\{{\bf{p}}\left( { - 1} \right)}\\{{\bf{p}}\left( 1 \right)}\\{{\bf{p}}\left( 3 \right)}\end{aligned}} \right)\).

  1. Show that \(T\) is a linear transformation.
  2. Find the matrix for \(T\) relative to the basis \(\left\{ {1,t,{t^2},{t^3}} \right\}\)for \({{\rm P}_3}\)and the standard basis for \({\mathbb{R}^4}\).

Question: In Exercises \({\bf{1}}\) and \({\bf{2}}\), let \(A = PD{P^{ - {\bf{1}}}}\) and compute \({A^{\bf{4}}}\).

1. \(P{\bf{ = }}\left( {\begin{array}{*{20}{c}}{\bf{5}}&{\bf{7}}\\{\bf{2}}&{\bf{3}}\end{array}} \right)\), \(D{\bf{ = }}\left( {\begin{array}{*{20}{c}}{\bf{2}}&{\bf{0}}\\{\bf{0}}&{\bf{1}}\end{array}} \right)\)

Let \({\bf{u}}\) be an eigenvector of \(A\) corresponding to an eigenvalue \(\lambda \), and let \(H\) be the line in \({\mathbb{R}^{\bf{n}}}\) through \({\bf{u}}\) and the origin.

  1. Explain why \(H\) is invariant under \(A\) in the sense that \(A{\bf{x}}\) is in \(H\) whenever \({\bf{x}}\) is in \(H\).
  2. Let \(K\) be a one-dimensional subspace of \({\mathbb{R}^{\bf{n}}}\) that is invariant under \(A\). Explain why \(K\) contains an eigenvector of \(A\).
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