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fluidistic
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Homework Statement
Consider the pray-predator model where the predator has an alternative way of surviving:
[itex]\dot x_1=\alpha _1x_1(\beta _1-x_1 )+\gamma _1 x_1 x_2[/itex]
[itex]\dot x_2=\alpha _2x_2(\beta _2-x_2 )-\gamma _2 x_1 x_2[/itex].
1)Show that the change of coordinates [itex]\beta _i y_i (t)= x_i \left ( \frac{t}{\alpha _i \beta _i } \right )[/itex] leads to the following system of DE's:
[itex]\dot y_1 =y_1 (1-y_1)+a_1 y_1 y_2[/itex]
[itex]\dot y_2 =y_2 (1-y_2)-a_2 y_1 y_2[/itex]
Where [itex]a_1=\frac{\gamma _1 \beta _2 }{\alpha_1 \beta _1}[/itex] and [itex]a_2=\frac{\gamma _2 \beta _1 }{\alpha _2 \beta _2}[/itex]
2)What are the stable equilibrium populations when i)[itex]0<a_2<1[/itex], ii)[itex]a_2>1[/itex]?
3)Suppose that [itex]a_ 1= 3 a_2[/itex] where [itex]a_2[/itex] is the a measure of the agressivity of the predator. What is the value of [itex]a_2[/itex] if the instinct of the predator consists of maximizing its population of stable equilibrium?
Homework Equations
Chain rule.
The Attempt at a Solution
For 1)
From the first DE of the first system of DE's I must reach [itex]\dot y_1=y_1 (1-y_1)+\frac{\gamma _1 \beta _2 }{\alpha _1 \beta _1} y_1y_2[/itex].
But using the change of coordinates, I get that [itex]\dot x_1=\alpha _1 \beta _1 ^2 \dot y_1 \Rightarrow \dot y_1 = \frac{\dot x_1 }{\alpha _1 \beta _1 ^2}=\frac{x_1 (\beta _1 -x_1)}{\beta _1 ^2}+\frac{\gamma _1 x_1 x_2}{\alpha _1 \beta _1 ^2}[/itex]. Now I don't know how to get rid of the x's and replace them by the y's. Probably with the change of coordinates but I don't see how. Any tip is appreciated.