Intersection points of two contour plots

[Luiz Melo]

Hi group,
Please consider the example below to illustrate my question (the
original problem is somehow much more complicated):

t1 = Table[Sin[3 x*y], {x, -3, 3, .1}, {y, -3, 3, .1}];

t2 = Table[If[x*y < 0, Sin[3 x*y]], {x, -3, 3, .1}, {y, -3, 3, .1}];

p1 = ListContourPlot[t1, Contours -> {0}, ContourShading -> False,
DataRange -> {{-3, 3}, {-3, 3}}, ContourStyle -> Black];

p2 = ListContourPlot[t2, Contours -> {0}, ContourShading -> False,
DataRange -> {{-3, 3}, {-3, 3}}, ContourStyle -> {Red, Dashed, Thick}];

Show[p1, p2]

Is there a way to show only the results of the intersection of these
two contour plots?

Thank you
Luiz

[djmpark]

Do you want something like this:

ContourPlot[Sin[3 x y], {x, -3, 3}, {y, -3, 3},

Contours -> {0},
ContourShading -> False,

ContourStyle -> Red,
RegionFunction -> Function[{x, y}, x y <= 0],
Exclusions -> {x == 0, y == 0}]


David Park
djm...@comcast.net
http://home.comcast.net/~djmpark/index.html

[Bob Hanlon]

ContourPlot[Sin[3 x*y] == 0,

{x, -3, 3}, {y, -3, 3},

RegionFunction ->
Function[{x, y}, x*y < 0],
Exclusions -> {x*y == 0},
ContourStyle -> Black]


or


t1 = Table[
If[x*y < 0, Sin[3 x*y], Sequence[]],

{x, -3, 3, .1}, {y, -3, 3, .1}];

ListContourPlot[t1,
Contours -> {0},
ContourShading -> False,
DataRange -> {{-3, 3}, {-3, 3}},

RegionFunction ->
Function[{x, y}, x*y < 0],
ContourStyle -> Black]



Bob Hanlon

[Luiz Melo]

Hi,
The given example was just to illustrate. In the original problem, I
cannot specify the region function. Also,
I have two tables t1 and t2 with a finite number of points, and I use
ListContourPlot with the option Contours -> {0} to see the contours at
z = 0. The solution to my problem occurs when both t1 and t2 intercept
at z = 0, as in the example given.

I can reformulate my problem in the following way: Given some contour plot

p0 = ListContourPlot[Table[Sin[3 x*y], {x, -3, 3, .1}, {y, -3, 3,
.1}], Contours -> {0}, ContourShading -> False,

DataRange -> {{-3, 3}, {-3, 3}}, ContourStyle -> Black];

How to extract the x and y coordinates of the plot p0 in the form of a
list of values t0 = {{x1,y2},{x2,y2},....} . ??
I found an old thread (mg98726) involving the same issue, but the
answer (mg98760) doesn't help much.

Thanks in advance.
Luiz

On Wed, May 1, 2013 at 9:56 AM, djmpark <djm...@comcast.net> wrote:
> Do you want something like this:
>

> ContourPlot[Sin[3 x y], {x, -3, 3}, {y, -3, 3},

> Contours -> {0},
> ContourShading -> False,

> ContourStyle -> Red,
> RegionFunction -> Function[{x, y}, x y <= 0],
> Exclusions -> {x == 0, y == 0}]
>
>
> David Park
> djm...@comcast.net
> http://home.comcast.net/~djmpark/index.html
>
>
> From: Luiz Melo [mailto:lm...@ufsj.edu.br]
>
>