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How to plot a differential equation?

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Sam
Sam 2017-11-6
评论： Steven Lord 2017-11-6
Hello,
I've got the following differential equation: dN(t)/dt - ((k - (a*N(t)))*N(t)) = f(t) This is the logistic law of population growth. N(t) = #individuals. dN(t)/dt = the derivative of N(t) = change of # individuals = #individuals/s. k = velocity of growth = 1/s. a = an inhibition factor on the growth = 1/(#individual*s). f(t) = production function = #individual/s.
I want to plot this equation. How can I do this?
  2 个评论
Torsten
Torsten 2017-11-6
Do you want to plot the equation or the solution to the equation ?
Best wishes
Torsten.
Sam
Sam 2017-11-6
The solution. So far I got this:
syms N(t);
ode = diff(N(t),t) == 2,309*N(t) - 2*N(t)^2;
cond = N(0) == 5;
NSol(t) = dsolve(ode, cond)
The solution is NSol(t) = 2*t + 5 I want to plot NSol by the command 'plot NSol' but it doesn't work...

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回答（1 个）

Torsten
Torsten 2017-11-6
编辑：Torsten 2017-11-6
ezplot(NSol,[0,4]);
Best wishes
Torsten.
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Torsten
Torsten 2017-11-6
ode = diff(N(t),t) == 2,309*N(t) - 2*N(t)^2;
I don't know what your ODE should look like, but the comma is wrong for certain.
Best wishes
Torsten.
Steven Lord
Steven Lord 2017-11-6
Yes. The decimal separator in MATLAB is period (.) not comma (,), and to enter numbers in the thousands or greater omit the comma. The comma operator separates commands, elements in an array, or function input or output arguments.
Specify that coefficient as 2.309 or 2309 instead of 2,309.

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