Ada Tutor: Outside Assignment 2 - Question to the Solution

Ada Tutor: Outside Assignment 2 - Question to the Solution

[Cedric]

Hi All,

I try to learn Ada using Ada Tutor (http://zhu-qy.blogspot.de/2012/08/adatutor.html). I tried the excerise of the outside assignment 2 and do not understand the given solution.

The test driver says that the tests

  Compare( 2,  4,  6, Not_A_Triangle);
  Compare( 1,  3,  2, Not_A_Triangle);
  Compare( 3,  1,  2, Not_A_Triangle);
  Compare( 1,  2,  4, Not_A_Triangle);
  Compare( 1,  4,  2, Not_A_Triangle);
  Compare( 4,  1,  2, Not_A_Triangle);

  Compare( 3,  3,  7, Not_A_Triangle);
  Compare( 3,  7,  3, Not_A_Triangle);
  Compare( 6,  3,  3, Not_A_Triangle);

do not define a valid triangle. The solution says

      if Len1 + Len2 <= Len3  or Len1 + Len3 <= Len2
         or Len2 + Len3 <= Len1  then
         Answer := Not_A_Triangle;

and 

You must have realized by now that it's impossible to draw a triangle with sides 1, 2, and 3.  The sum of any two sides must be greater than the third.

What is the exact mathematic definition of a triangle? My last math course a quick a while ago :(

I would assume that a triangle formed by 1, 2 and 3 would give a valid triangle. Why should that not be the case?

Regards

Cedric

Re: Ada Tutor: Outside Assignment 2 - Question to the Solution

[Georg Bauhaus]

On 20.12.12 00:18, Cedric wrote:
> You must have realized by now that it's impossible to draw a triangle with sides 1, 2, and 3.  The sum of any two sides must be greater than the third.
>
> What is the exact mathematic definition of a triangle? My last math course a quick a while ago:(
>
> I would assume that a triangle formed by 1, 2 and 3 would give a valid triangle. Why should that not be the case?

(It has helped me, and, in fact, a few kids I know if you don't mind,
to represent these abstract lengths (if that's what they are) as steps
a man can walk. If one person walks for 1 step, then 2 ... how far
would this person have got in steps? What about some other person
taking three steps on a straight line?
If you flattened the two shorter paths by "bending" them towards
the 3-step path, what happens?)

Re: Ada Tutor: Outside Assignment 2 - Question to the Solution

[Adam Beneschan]

On Wednesday, December 19, 2012 3:18:00 PM UTC-8, Cedric wrote:
 
> I would assume that a triangle formed by 1, 2 and 3 would give a valid triangle. Why should that not be the case?

I'd recommend trying it yourself ... cut three pieces of string whose lengths are 1, 2, and 3 inches (or 1, 2, and 3 cm if you prefer; or if that's too small, try 3, 6, and 9 cm).  Then try to make a triangle.  I think you'll see what the problem is.

                         -- Adam

Re: Ada Tutor: Outside Assignment 2 - Question to the Solution

[Manuel Collado]

El 20/12/2012 1:15, Adam Beneschan escribi�:
> On Wednesday, December 19, 2012 3:18:00 PM UTC-8, Cedric wrote:
>
>> I would assume that a triangle formed by 1, 2 and 3 would give a
>> valid triangle. Why should that not be the case?
>
> I'd recommend trying it yourself ... cut three pieces of string whose
> lengths are 1, 2, and 3 inches (or 1, 2, and 3 cm if you prefer; or
> if that's too small, try 3, 6, and 9 cm).  Then try to make a
> triangle.

They make a perfectly valid (degenerated) triangle:
   A B   C
   *-*---*

With sides 1,2 and 3, and angles 0�, 180� and 0�.


> I think you'll see what the problem is.

Of course. The problem is to agree if a degenerated triangle is or not 
an acceptable triangle.

-- 
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado

Re: Ada Tutor: Outside Assignment 2 - Question to the Solution

[Georg Bauhaus]

On 20.12.12 10:13, Manuel Collado wrote:
> The problem is to agree if a degenerated triangle is or not an acceptable triangle.

I think it the tutorial states what the sum of two sides
should be in relation to the third.

When will academia stop messing up teaching basics
of formal things, such as programming, by shifting
attention to other branches of mathematics, such
as geometry?

Re: Ada Tutor: Outside Assignment 2 - Question to the Solution

[Stephen Leake]

Cedric <Cedric.Lannock@gmx.net> writes:

> What is the exact mathematic definition of a triangle? My last math
> course a quick a while ago :(

http://en.wikipedia.org/wiki/Triangle:

    In Euclidean geometry any three points, when non-collinear,
    determine a unique triangle and a unique plane (i.e. a
    two-dimensional Euclidean space).

-- 
-- Stephe