[Gambas-user] gb3: "Mathematic error"

[Kevin Fishburne]

On 01/17/2012 05:18 AM, Kevin Fishburne wrote:
> On 01/16/2012 02:33 AM, Benoît Minisini wrote:
>> Le 16/01/2012 08:05, Kevin Fishburne a écrit :
>>> On 01/16/2012 01:43 AM, Kevin Fishburne wrote:
>>>> Why would I get the runtime error "Mathematic error" in this function:
>>>>
>>>> Public Function Distance(x1 As Single, y1 As Single, x2 As Single, y2 As
>>>> Single) As Single
>>>>        Return Abs(Sqr((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)))
>>>> End
>>>>
>>>> The values of the variables are:
>>>>
>>>> ?x2&     ""&     x1&     ""&     x2&     ""&     x1&     ""&     y2&     ""&     y1&     ""&     y2&
>>>> ""&     y1
>>>>
>>>> 174.248779296875 2.40799128109576E-41 174.248779296875
>>>> 2.40799128109576E-41 146.759170532227 7.19552647834628E+27
>>>> 146.759170532227 7.19552647834628E+27
>>>>
>>>> Using GAMBAS 3, revision unknown. I'm recompiling now to see if it makes
>>>> a difference, but please let me know what this error means and what
>>>> could cause it.
>>>>
>>> I changed the first line (old one) to the second:
>>>
>>> 'Return Abs(Sqr((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)))
>>> Return Sqr((x2 - x1) ^ 2 + (y2 - y1) ^ 2)
>>>
>>> and it gives me no problems. Seems like I really screwed up the distance
>>> calculation, but even so this may be a bug so hopefully I've contributed
>>> to a solution. Still curious of course as to what the error might mean.
>>> Maybe it should just say "You suck at math." :)
>>>
>> You get a mathematic error because of an overflow. (y2 - y1) * (y2 - y1)
>> cannot be expressed by a Single in your example.
>>
>> The "^" operator deals with Float internally, so you don't get an error.
>>
>> Anyway, to compute a distance, you can use the Hyp() or the Mag()
>> function. It will be faster.
> Sometimes it calculates without error, other times it doesn't. Changing
> all the datatypes to float doesn't make any difference either. Thanks
> for the efficiency tip on Hyp() and Mag(), but it still looks like
> there's a problem with math here. How should a manual distance
> calculation be expressed without overflow if that's the problem?
>

Just discovered it has to do with one of the passed values being zero. 
Why is that?

-- 
Kevin Fishburne
Eight Virtues
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