I am trying to pass NAN value based upon some condition to func Vq but i am getting 20 instead of NAN.

Vq(x,y) = select(xq(x,y) < 20, NAN, Expr(1.0f));

But
Vq(x,y) = select(xq(x,y) < 20, 100, Expr(1.0f)); is working fine.

Can any one please explain me why this is happening? How can I pass NAN value based upon some condition

Thanks