nag_create_nan (x07bbc) sets x to be a quiet or a signalling NaN (Not A Number).
IEEE (2008) Standard for Floating-Point ArithmeticIEEE Standard 754-2008 IEEE, New York.
quiet – IntegerInput
On entry: determines whether a quiet or a signalling NaN is to be created. If , the returned NaN is quiet, otherwise it is signalling. See reference IEEE (2008) for the distinction between the two kinds.