integer a function in matlab

[ginafort]

Please what commande i must to use in matlab for integrate my function: dg/dt = f(t)
thank you to orient me

[Greg Heath]

On Sep 2, 1:39 pm, ginafort <najl...@yahoo.fr> wrote:
> Please what commande i must to use in matlab for integrate my function: dg/dt = f(t)
> thank you to orient me

>> lookfor integral
...
QUAD Numerically evaluate integral, adaptive Simpson quadrature.
QUAD8 Numerically evaluate integral, higher order method.
QUADL Numerically evaluate integral, adaptive Lobatto quadrature.
...

Hope this helps.

Greg

[ginafort]

thanks greg,
but i want to have a primitive function, i want to draw a primitive of my function.
with the commande "quad" i must to have the bounds of the integral

[Wayne King]

ginafort <naj...@yahoo.fr> wrote in message <1315703166.159523.1283...@gallium.mathforum.org>...

> thanks greg,
> but i want to have a primitive function, i want to draw a primitive of my function.
> with the commande "quad" i must to have the bounds of the integral

Hi, do you want to integrate symbolically? If you have the Symbolic Toolbox, you can do the following:

syms x y
y = x^2;
z=int(y)

The above gives the antiderivative with the constant of integration equal to zero.

% Now plot the derivative and antiderivative
ezplot(y,[-5 5]); hold on;
h = ezplot(z,[-5 5]);
set(h,'linewidth',2,'color',[1 0 0 ]);
title('x^2 and x^3/3');

Hope that helps,
Wayne

[ginafort]

I have dg/dt=.... and i want to plot g=f(t).
how to de it in matlab?
please your help

[Pete]

Consider the integral as an ODE for g (as a special case where the RHS
does not depend on g).

Then use a standard ODE solver with odefun=f(t) and initial condition
g(t0)=0.

For example:

f=@(t,y) t.^2.*exp(-t);
[t,g] = ode45(f,[0,10],0);
plot(t,g);

Good luck,
Pete