On 22/10/2013 1:07 PM, John Van Praag wrote:
Does R have any facilities, or packages, for graphing complex functions?
I don't think base R does, but if you have a complex-valued function of
a real variable, it wouldn't be hard to write one.
For your example:
library(rgl)
xvals <- seq(0, 2*pi, len=256)
f <- function(x) cos(x) + 1i * sin(x)
zvals <- f(xvals)
plot3d(xvals, Re(zvals), Im(zvals), type="l")
For the case of a real-valued function of a complex variable, you could
use persp() or persp3d(). For both argument and value being complex,
you'll need 4 dimensions, and that's hard to do nicely, though I suppose
you could overlay contour or perspective plots of the real and imaginary
parts of the value. For example:
x <- y <- seq(0, 2*pi, len=50)
z <- outer(x, y, function(x,y) x + 1i*y)
zvals <- f(z)
persp3d(x, y, Re(zvals), col="red", alpha=0.5, xlab="Re(z)",
ylab="Im(z)", zlab="f(z)")
surface3d(x, y, Im(zvals), col="blue", alpha=0.5)
Duncan Murdoch
I find that 'curve' does not do the trick. Example:
> f = function(x) cos(x) + 1i * sin(x)
> curve(f, -pi, pi)
Error in xy.coords(x, y, xlabel, ylabel, log) :
(converted from warning) imaginary parts discarded in coercion
Enter a frame number, or 0 to exit
1: curve(f, -pi, pi)
2: plot(x = x, y = y, type = type, xlab = xlab, ylab = ylab, xlim = xlim,
log = lg, ...)
3: plot.default(x = x, y = y, type = type, xlab = xlab, ylab = ylab, xlim =
xlim, log = lg, ...)
4: xy.coords(x, y, xlabel, ylabel, log)
5: .signalSimpleWarning("imaginary parts discarded in coercion",
quote(xy.coords(x, y, xlabel, ylabel, log)))
6: withRestarts({
.Internal(.signalCondition(simpleWarning(msg, call), msg, call))
.Internal(.dfltWarn(msg, call))
}, muffleWarning = function() NULL)
7: withOneRestart(expr, restarts[[1]])
8: doWithOneRestart(return(expr), restart)
9: (function ()
{
error()
utils::recover()
})()
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