Am 21.12.2016 um 06:49 schrieb omniverse:

> Just looked at what clock says it is when trying equal frames.
> 
> -nan(ind)
> 
> Not a number (with a dash, minus??), but I don't know what the ind means.
> Thought you probably would.

Yes: "Indeterminate". Meaning that the expression has no solution at all
(not even infinity), or that it has more than one solution (typically
infinitely many).

For example, the expression

    a / b

is supposed to yield the number x that satisfies

    x * b = a

so the expression

    0 / 0

should yield the number x that satisfies

    x * 0 = 0

which is true for all numbers, so the computer can't decide on any
particular one to give as a result.


At the other end of the spectrum, the expression

    sqrt(-1)

has no answer at all in the set of real numbers, so the computer is
again can't give you any meaningful result.


A slightly different case is the expression

    1 / 0

for which some mathematical systems add two special values to the set of
real numbers, named "positive infinity" (defined as 1/0) and "negative
infinity" (defined as -1/0), so in this case the computer does have a
result to present -- which is still "not a number" though, so it is
reported in a similar way:

    nan(inf)


Not sure what that minus sign means. Might be just an intrinsic part of
the way "Not-a-Number" values are reported, or might actually mean
_something_. Maybe the IEEE would know.

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