## 4 Reputation

14 years, 105 days

## thank you very much, I tried...

thank you very much,

I tried both implicit and numeric ways, and they work.

very excited to learn the implicit way, and, yeah I should have used the numeric in dsolve so I would not have run into the integration in the first place.

## This post is the same as the second post...

I have to plot the solutions of a population growth model :

diff(P(t),t) = .48*P(t) - .028*P(t)^2 - 2*P(t)^2 / (4 + P(t)^2)

1. use an initial value you desire

2.plot the solution for the model above

3. try another initial value and repeat 2.

This is my command but it doesn't work

1. eq:= diff(P(t),t) = .48*P(t) - .028*P(t)^2 - 2*P(t)^2 / (4 + P(t)^2);

2. sol:= dsolve({eq, P(0)=8}, P(t));

#This gives RootOf(some very complex and messy integration in terms of d_a, _a, _b, _Z, and t)

3. with(plots):

plot(rhs(sol), t=0..15);

#This gives an empty graph and a warning => unable to evaluate the function to numeric values in the region;

## more complex problem...

I have to plot the solutions of a population growth model :

diff(P(t),t) = .48*P(t) - .028*P(t)^2  - 2*P(t)^2  / (4  + P(t)^2)

1. use an initial value you desire

2.  plot the solution for the model above

3. try another initial value and repeat 2.

### this is my command but it doesn't work

1. eq:= diff(P(t),t) = .48*P(t) - .028*P(t)^2  - 2*P(t)^2  / (4  + P(t)^2)

2. sol:= dsolve({eq, P(0)=8}, P(t));

#This gives RootOf(some very complex and messy integration in terms of d_a, _a, _b, _Z, and t)

3. with(plots):

plot(rhs(sol), t=0..15);

#This gives an empty graph and a warning => unable to evaluate the function to numeric values in the region;

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