Re: Can plot take limits? Or something like it ...
- To: mathgroup at smc.vnet.net
- Subject: [mg43197] Re: Can plot take limits? Or something like it ...
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Mon, 18 Aug 2003 02:50:56 -0400 (EDT)
- References: <bhkkim$pbg$1@smc.vnet.net>
- Reply-to: "Allan Hayes" <hay at haystack.demon.co.uk>
- Sender: owner-wri-mathgroup at wolfram.com
Mathieu,
David Park has pointed out the reason for the difference: the sample points
for Plot do not include x = 0 wherease those for those for Plot3D do.
We can introduce limit explicitely: the following both work
Plot[Limit[Sin[s]/s, s -> x], {x, 0, 1}]
Plot3D[Limit[y*Sin[s]/s, s -> x], {x, 0, 1}, {y, 0, 1}]
Unfortunately, Limit does not work for two variables, so we cannot use this
trick for the general Plot3D situation (and, of course even limits over one
variable cannot always be calculated)
Allan
---------------
Allan Hayes
hay at haystack.demon.co.uk
Voice: +44 (0)116 241 8747
Fax: +44 (0)870 164 0565
"Mathieu McPhie" <mathieu_mcphie at yahoo.com.au> wrote in message
news:bhkkim$pbg$1 at smc.vnet.net...
> Hello friendly helpers and knowledgable personages,
>
> I'm sure this is a problem encountered (and answered) before. And it
> is just one of the many I have encountered with this drat perverse
> progam. Anyway ...
>
> The following two commands (this is an extremely cut down version of
> my problem so try and be general)
>
> Plot[Sin[x]/x, {x, 0, 1}]
> Plot3D[y*Sin[x]/x, {x, 0, 1}, {y, 0, 1}]
>
> The first works perfectly, correctly going toward the limit at x=0 of
> 1.
>
> For the second I get ...
>
> Power::infy : Infinite expression 1/0. encountered.
>
> \[Infinity]::indet : Indeterminate expression 0. ComplexInfinity
> encountered.
>
> Plot3D::plnc: y*Sin[x]/x is neither a machine-size real number at
> {x,y}={0., 0.} nor a list of a real number and a valid color
> directive.
>
> Please explain, Vielin Dank, Mathieu McPhie
>