Exercise 2.3.3 For each ODE sketch a phase portrait by hand, following the procedure of Examples 2.10, 2.11, and 2.12. Classify each fixed point as asymptotically stable or unstable. Use the result to sketch solutions for the given initial conditions on pair of tu axes with a reasonable range for u. (a) u'(t)=-u(t), sketch solutions with u(0) = 2 and u(0) = -2. (b) v(t)=11-2v(t), sketch solutions with v(0) = 0 and v(0) = 15. H (c) v(t)=11-kv(t) (k a positive constant), sketch solutions with v(0) = 0 and v(0) = 15/k. (d) u' (t) = -(u(t)-1) (u(t)-3), sketch solutions with u(0) = 1/2, u(0) = 2, and u(0) = 4. (e) u' (t) = u(t)(1-u(t))-u(t)/10 (the harvested logistic equation (1.12) with r=1 = 1, K=1, and h=1/10), sketch solutions with u(0) = 1/2 and u(0) = 3/2. Note only u 20 makes physical sense here. What is the long-term fate of the species?

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Chapter2: Second-order Linear Odes
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do b and c

Exercise 2.3.3 For each ODE sketch a phase portrait by hand, following the procedure of
Examples 2.10, 2.11, and 2.12. Classify each fixed point as asymptotically stable or unstable.
Use the result to sketch solutions for the given initial conditions on pair of tu axes with a
reasonable range for u.
(a) u' (t) = -u(t), sketch solutions with u(0) = 2 and u(0) = -2.
(b) v (t)=11-2v(t), sketch solutions with v(0) = 0 and v(0) = 15.
(c) v(t)=11-kv(t) (k a positive constant), sketch solutions with v(0) = 0 and v(0) = 15/k.
(d) u'(t)=-(u(t)-1)(u(t)-3), sketch solutions with u(0) = 1/2, u(0) = 2, and u(0) = 4.
(e) u' (t) = u(t)(1-u(t))-u(t)/10 (the harvested logistic equation (1.12) with r = 1, K = 1,
and h=1/10), sketch solutions with u(0) = 1/2 and u(0) = 3/2. Note only u ≥ 0 makes
physical sense here. What is the long-term fate of the species?
(f) u' (t) = u(t) (1-u(t))-2u(t) (the harvested logistic equation (1.12) with r = 1, K = 1,
and h=2), sketch solutions with u(0) = 1/2 and u(0) = 3/2. Note only u ≥ 0 makes
physical sense here. What is the long-term fate of the species?
-
(g) u' (t) = rc₁-ru(t)/V (the conservation law ODE (1.5) with r, c₁, V> 0). Recall that this
model is only appropriate for u 20. Label the fixed point(s) in terms of r, c₁, and V, and
sketch solutions for which u(0) = 0 and u(0) = 2c₁V.
00 160
telefon el fallimbed ODE (25ith wh 0) Recall that this model
Transcribed Image Text:Exercise 2.3.3 For each ODE sketch a phase portrait by hand, following the procedure of Examples 2.10, 2.11, and 2.12. Classify each fixed point as asymptotically stable or unstable. Use the result to sketch solutions for the given initial conditions on pair of tu axes with a reasonable range for u. (a) u' (t) = -u(t), sketch solutions with u(0) = 2 and u(0) = -2. (b) v (t)=11-2v(t), sketch solutions with v(0) = 0 and v(0) = 15. (c) v(t)=11-kv(t) (k a positive constant), sketch solutions with v(0) = 0 and v(0) = 15/k. (d) u'(t)=-(u(t)-1)(u(t)-3), sketch solutions with u(0) = 1/2, u(0) = 2, and u(0) = 4. (e) u' (t) = u(t)(1-u(t))-u(t)/10 (the harvested logistic equation (1.12) with r = 1, K = 1, and h=1/10), sketch solutions with u(0) = 1/2 and u(0) = 3/2. Note only u ≥ 0 makes physical sense here. What is the long-term fate of the species? (f) u' (t) = u(t) (1-u(t))-2u(t) (the harvested logistic equation (1.12) with r = 1, K = 1, and h=2), sketch solutions with u(0) = 1/2 and u(0) = 3/2. Note only u ≥ 0 makes physical sense here. What is the long-term fate of the species? - (g) u' (t) = rc₁-ru(t)/V (the conservation law ODE (1.5) with r, c₁, V> 0). Recall that this model is only appropriate for u 20. Label the fixed point(s) in terms of r, c₁, and V, and sketch solutions for which u(0) = 0 and u(0) = 2c₁V. 00 160 telefon el fallimbed ODE (25ith wh 0) Recall that this model
■ Example 2.10 Let us sketch a phase portrait for the autonomous ODE u' (t) = u²(t) - 1. In this
case the ODE is u' = f(u) with f(u) = u² - 1 and the fixed points are the solutions to f(u) = 0,
that is, u² − 1 = 0. These fixed points are u = -1 and u = 1, shown as the blue dots in the u axis in
Figure 2.7.
1
The fixed points divide the u axis into intervals (-∞, -1), (-1, 1), and (1,0). If u < -1 then
f(u) > 0, so solutions in this interval increase. If −1 < u < 1 then f(u) < 0, so solutions in this
interval decrease. If u > 1 then f(u) > 1 and solutions in this interval increase. This is summarized
2.3 Qualitative and Graphical Insights
-1
0
1
Figure 2.7: Phase portrait for the ODE u'=u²-1.
53
in the phase portrait of Figure 2.7; the arrows between the fixed points indicate whether solutions
increase or decrease in that interval.
Reading Exercise 2.3.4 Sketch a phase portrait for the autonomous ODE u' (t) = u²(t)-2u(t)-3
Transcribed Image Text:■ Example 2.10 Let us sketch a phase portrait for the autonomous ODE u' (t) = u²(t) - 1. In this case the ODE is u' = f(u) with f(u) = u² - 1 and the fixed points are the solutions to f(u) = 0, that is, u² − 1 = 0. These fixed points are u = -1 and u = 1, shown as the blue dots in the u axis in Figure 2.7. 1 The fixed points divide the u axis into intervals (-∞, -1), (-1, 1), and (1,0). If u < -1 then f(u) > 0, so solutions in this interval increase. If −1 < u < 1 then f(u) < 0, so solutions in this interval decrease. If u > 1 then f(u) > 1 and solutions in this interval increase. This is summarized 2.3 Qualitative and Graphical Insights -1 0 1 Figure 2.7: Phase portrait for the ODE u'=u²-1. 53 in the phase portrait of Figure 2.7; the arrows between the fixed points indicate whether solutions increase or decrease in that interval. Reading Exercise 2.3.4 Sketch a phase portrait for the autonomous ODE u' (t) = u²(t)-2u(t)-3
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