Inequations and PointIn-Command

Birgit Lachner shared this problem 8 years ago
Answered

1.) I you have an inequation like y>0 or x<0 and you create a point with the PointIn-Tool the created point become a slider on one of the axes. The same happens with x>=1. It works fine with inequations with two variables.


2.) I have three inequations a,b and c and defined A = PointtIn[a(x) ∧ b(y) ∧ c(x, y)]. It works more or less fine but if I wanted to move the point to the borders. I could not move the point everytime to the borders. If I do it again and again, the movement of the point sometimes stopps when it on the border, sometimes when the point-circle is touching the border and sometimes when it is "far" away from the border. The behaviour is not influenced if the inequations are < or <=.


Birgit

Comments (5)

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4.0.41

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1) Works for me in GG5 on W7 Java 7. I can get the point to move freely in the region. The description you give matches the result you get by using Point[] rather than PointIn[].


2) I also experienced problems with this. The point would not go exactly on to the border parallell to the y-axis, and CPU usage increased. I also got an "undefined" result first time I defined the point - possibly because the origin (0,0) was not part of the region. I had to take away the sloping inequality c to get a working point and then put it back again.

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If you use the PointIn-Command in the input line it works fine. Only the tool causes the problem.


In Version 5 I have the same behaviour:

- define x>0 (called a)

- use PointIn-tool and click on a

- Point becomes a slider on xAxis

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Hi,


ad 1) there is a difference between Point[x>0] (has one degree of freedom, moves on x-axis) and PointIn[x>0]. I guess the Point In tool should use the latter.


ad 2) if the mouse pointer is outside of the inequality and the algorithm fails to find point on border close to the mouse pointer, last position of the point that was inside of the inequality is used and the behavior is not very nice (the faster you move the mouse pointer, the further from border the resulting point is). It should not happen if all your inequalities are linear.


Cheers,

Zbynek

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ad 1.) I understand the difference well. Please try the tool. It does not work correctly!

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