On Aug 11, 2010, at 11:16 AM, ba ba wrote:
Dear All,
I tried to plot contour lines using R function contour, but got the
results
which are not expected.
require(RTOMO)
x <- seq(-1,1,0.1)
y <- seq(-1,1,0.1)
xy <- meshgrid(x,y)
z <- xy$x^2+ 3*xy$y^2
contour(x,y,z,col="blue",xlab="x",ylab="y")
The above code gave me the contour graph for z=3*x^2+y^2 rather than
z=x^2+3*y^2. Is anyone know the reason?
Because contour was expecting a matrix of z values for z and you gave
it a list created by a function you did not understand?
> meshgrid
function (a, b)
{
return(list(x = outer(b * 0, a, FUN = "+"), y = outer(b,
a * 0, FUN = "+")))
}
Instead:
Use the base function outer():
> x <- seq(-1,1,0.1)
> y <- seq(-1,1,0.1)
> xy <- outer(x,y, FUN=function(x,y) x^2+ 3*y^2)
>
>
> contour(x,y,xy,col="blue",xlab="x",ylab="y")
--
David Winsemius, MD
West Hartford, CT
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