#2552 What should imag(NaN) be?

[Anonymous]

It's probably no bug, because maybe some C function does is like that.
But maybe somebody can explain why imag(NaN) == 0 instead of NaN?

So, then NaN is only a "real"-Not-a-Number but not a complex one?

PS.
I remember a similar case about sgn(NaN) == 0.

Examples:

j = {0,1}

c1 = 1   + j*2
c2 = NaN + j*2
c3 = 1   + j*NaN
c4 = NaN + j*NaN

print c1
print c2
print c3
print c4
print ""
print real(c1), imag(c1)
print real(c2), imag(c2)
print real(c3), imag(c3)
print real(c4), imag(c4)
print ""
print real(NaN)
print imag(NaN)

Result:

{1.0, 2.0}
NaN
NaN
NaN

1.0 2.0
NaN 2.0
NaN NaN
NaN NaN

NaN
0.0

[Ethan Merritt]

Good question.
That is one of a longer list of similar questions I have filed under "decisions to be made before the development version becomes a release candidate"

• should sgn(NaN) return 0 or NaN?
• should imag(NaN) return 0 or NaN?
• should sgn(foo) return an int if foo is an int, cmplx otherwise?
• should any of the built-in math functions return +Inf or -Inf as opposed to NaN or VERYLARGE? For example, what should gamma(-1) return?

I had figured to eventually post the list to gnuplot-beta for discussion, but any thoughts you have now are welcome.

I tried to see what C, Fortran, or other languages do with regard to sgn(foo) but did not find any useful guidance. Maybe it's covered in some IEEE standard?