Many thanks Duncan. I got the plot even I don't really understand the whole
command..
I will study that later..

:-)

Regards



On Sun, Nov 22, 2009 at 4:44 PM, Duncan Murdoch <murdoch@stats.uwo.ca>wrote:

>  On 22/11/2009 11:27 AM, Rofizah Mohammad wrote:
>
>> Hi,
>>
>> If I have 2D data set say (x,y) and I can do scatter plot by using
>> plot(x,y)
>> command.
>> How can I add in this scatter plot the equations curve say
>>
>> 2X2 + 3Y2 – 6X – 7Y + 9 = 0.
>>
>
> You could do it using contour(), but you should use an equation that has
> some real solutions.  For example, using a different equation than yours:
>
> x <- rnorm(100, sd=1)
> y <- rnorm(100, sd=1)
> xgrid <- seq(min(x), max(x), len=100)
> ygrid <- seq(min(y), max(y), len=120)
> grid <- expand.grid(x=xgrid, y=ygrid)
> LHS <- function(x, y) x^2 + y^2 - x - y  - 1
> z <- apply(grid, 1, function(x) LHS(x[1], x[2]) )
> z <- matrix(z, 100, 120)
> plot(x,y)
> contour(xgrid, ygrid, z, levels=0, add=TRUE)
>

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