How to plot a differential equation?

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?

[Torsten]

Do you want to plot the equation or the solution to the equation ?

Best wishes

Torsten.

[Sam]

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...

Answer 1

[Torsten]

ezplot(NSol,[0,4]);

Best wishes

Torsten.

[Sam]

I noticed the solution for my second order differential equation is just a straight line... This can't be right...

[Torsten]

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]

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.