Thanks a lot! I got it! I haven't set the level before.Hao

On Sat, Jul 4, 2009 at 6:33 PM, Duncan Murdoch <murdoch@stats.uwo.ca> wrote:

> On 04/07/2009 3:31 PM, Hao Jiang wrote:
>
>> Hi Duncan,Thanks!
>>
>> But I still get a little confused about outer() func. Would give me a
>> simple
>> example to contour it? Just like the formula x^2 + y^2 + x + y -5 = 0.
>> (Sorry I am a newbie to R, found really hard to use the R manual)
>>
>
> > x <- seq(-6,6,len=100)
> > y <- seq(-4,4,len=100)
> > z <- outer(x,y, function(x,y) x^2 + y^2 + x + y -5)
> > contour(x,y,z,levels=0)
>
> This will draw a contour of the solutions to the equation.  (I set the
> ranges of x and y differently just so I could be sure I got them in the
> right order in the outer and contour functions.)
>
> Duncan Murdoch
>
>
>
>> Thanks,
>> Hao
>>
>> On Sat, Jul 4, 2009 at 7:10 AM, Duncan Murdoch <murdoch@stats.uwo.ca>
>> wrote:
>>
>>  Hao Jiang wrote:
>>>
>>>  Hi,
>>>> I want to plot a polynomial in the form like ax^2 + bxy + cy^2 + dx + ey
>>>> +
>>>> f
>>>> =0 without solving it(since I may have 3 or 4 dimensional polynomial and
>>>> it's really hard to solve). Is there any way  to plot this kind of
>>>> polynomial?
>>>>
>>>> Thanks a lot!
>>>>
>>>>  There are lots of ways.  A contour plot is probably most informative, a
>>> persp plot is prettier.  In either case you need to evaluate the
>>> polynomial
>>> on a grid, and pass the matrix of values to the plotting function.
>>>
>>> The outer() function is handy for doing the grid evaluation.
>>>
>>> Duncan Murdoch
>>>
>>>
>>
>

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