[Gambas-user] gb3: incorrect solution to If...Then condition

[Jussi Lahtinen]

At least the problem is unrelated to sin and cos...

? format(0.47942553860420300027 ^ 2 -
0.22984884706593014129,"#.######################")
- .0000000000000012212453

? format(0.47942553860420300027 ^ 2.0 - 0.22984884706593014129
,"#.######################")
- .0000000000000011379786


Jussi





2012/4/28 Benoît Minisini <gambas at ...1...>

> Le 27/04/2012 20:44, Jussi Lahtinen a écrit :
> > If Sin(0.5) ^ 2 + Cos(0.5) ^ 2<>  1 Then
> > Print "This shouldn't be seen, but it is."
> > Endif
> >
> >
> > ? format((Sin(0.5) ^ 2 + Cos(0.5) ^ 2),"#.########################")
> > 1
> >
> > What is going on?
> >
> >
> > Jussi
> >
>
> It's very strange actually.
>
> There is optimization in the "^" operator. If the power is an integer
> between -4 and +4, standard multiplication and division are used instead
> of the pow() mathematical function.
>
> In other words, Sin(0.5) ^ 2 = Sin(0.5) * Sin(0.5).
>
> If you want to force the use of the pow() function, write 'Sin(0.5) ^ 2.0'.
>
> And then comes the strangeness: Sin(0.5) * Sin(0.5) does not return the
> same value as Sin(0.5) ^ 2.0 ! And Sin(0.5) ^ 2.0 + Cos(0.5) ^ 2.0 does
> return 1.0. But not Sin(0.5)*Sin(0.5) + Cos(0.5)*Cos(0.5), which should
> be more accurate!
>
> If someone has an explanation...
>
> --
> Benoît Minisini
>
>
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