> class Triangle
> def area
> pts = [@a, @b, @c]
> #filter out degenerate triangles
> return 0 if pts.uniq!
> ...
Only a couple of small things. You want to return 0 if Vector objects
happen to be uniq!? Or, are you using my nested array model? For
example...
[Vector[1, 1], Vector[1, 1], Vector[1, 1]].uniq!
=> nil
Ah. This illustrates the ( joys | perils ) of test-driven development.
The solution was failing Matt's test cases for degenerate triangles,
The uniq! test was my attempt of to filter out triangles with duplicate
points (they were causing NANs). I assumed Vectors with identical
contents would compare equal. But this method only passed the tests
because the case was creating Triangles with multiple instances of
the same Vector. I guess it should be:
return 0 if pts.map{|v|v.to_a}.uniq!
Also, "bad" triangles can have legs that are almost collinear, which,
depending on your use case, you might have to check for. I didn't.
This solution handles that without a special case: if the legs are
colinear, both will fall on the X axis after rotation, making the height 0.
If they are only 'almost colinear', then the math should handle it.
Here's another test case for those types of triangle:
def test_linear
#colinear
t = Triangle[Vector[0,0],Vector[1,1],Vector[-1,-1]]
assert_in_delta(0, t.area, TOL)
t = Triangle[Vector[2.5,1.1],Vector[5,2.2],Vector[7.5,3.3]]
assert_in_delta(0, t.area, TOL)
#nearly colinear
t = Triangle[Vector[2.5,1.1],Vector[5,2.2],Vector[7.5,3.301]]
assert_in_delta(0.00125, t.area, TOL)
[1e-3,1e-6,1e-9].each{|n|
t = Triangle[Vector[0,0],Vector[n,1],Vector[0,2]]
assert_in_delta(n, t.area, n*TOL)
}
end
-Adam
···
On 4/21/08, Todd Benson <caduceass@gmail.com> wrote:
On Mon, Apr 21, 2008 at 6:50 PM, Adam Shelly <adam.shelly@gmail.com> wrote:
