J3/02-228 Date: 14 July 2002 To: J3 From: Dan Nagle Subject: Atan2 & Log In comp.lang.fortran, James Giles complained that the specified return values for atan2 & log were wrong. There was no subsequent discussion on the mailing list to clarify the issue. So I guess everybody's happy with Giles' words. The edits below use Giles' words from his comp.lang.fortran posting. Hopefully, if I've fouled things up, J3 will correct it before the meeting. Edits: 301:24-29 Replace the result value paragraph with the following: "The result has a value equal to a processor-dependent approximation to the principal value of the argument of the complex number (X, Y), expressed in radians. It lies in the range -pi <= ATAN2(Y,X) <= pi and is equal to a processor-dependent approximation to a value of arctan(Y/X) if X /= 0. If Y is positive, the result is positive. If Y is negative, the result is negative. If Y = 0, the absolute value of the result is zero if X is positive and the absolute value of the result is pi if X is negative. If X = 0, the absolute value of the result is pi/2." 324:13-16 Replace the result value paragraph with the following: "The result has a value equal to a processor-dependent approximation to LOG(X). A result of type complex is the principal value with the real part equal to LOG(ABS(X)) and the imaginary part equal to ATAN2(Ix, Rx), where Rx is the real part of X and Ix is the imaginary part of X."