Nächste: Functions and Variables for plotdf, Vorige: plotdf, Nach oben: plotdf [Inhalt][Index]
The function plotdf
creates a plot of the direction field (also
called slope field) for a first-order Ordinary Differential Equation
(ODE) or a system of two autonomous first-order ODE’s.
Plotdf requires Xmaxima. It can be used from the console or any other interface to Maxima, but the resulting file will be sent to Xmaxima for plotting. Please make sure you have installed Xmaxima before trying to use plotdf.
To plot the direction field of a single ODE, the ODE must be written in the form:
dy -- = F(x,y) dx
and the function F should be given as the argument for
plotdf
. If the independent and dependent variables are not x,
and y, as in the equation above, then those two variables should
be named explicitly in a list given as an argument to the plotdf command
(see the examples).
To plot the direction field of a set of two autonomous ODE’s, they must be written in the form
dx dy -- = G(x,y) -- = F(x,y) dt dt
and the argument for plotdf
should be a list with the two
functions G and F, in that order; namely, the first
expression in the list will be taken to be the time derivative of the
variable represented on the horizontal axis, and the second expression
will be the time derivative of the variable represented on the vertical
axis. Those two variables do not have to be x and y, but if
they are not, then the second argument given to plotdf must be another
list naming the two variables, first the one on the horizontal axis and
then the one on the vertical axis.
If only one ODE is given, plotdf
will implicitly admit
x=t
, and G(x,y)=1
, transforming the non-autonomous
equation into a system of two autonomous equations.
Nächste: Functions and Variables for plotdf, Vorige: plotdf, Nach oben: plotdf [Inhalt][Index]