ATAN2(Y, X)

Purpose

Arctangent (inverse tangent) function. The result is the principal value of the nonzero complex number (X, Y) formed by the real arguments Y and X.

Class

Elemental function

Argument type and attributes

Y

An INTENT(IN) REAL

X

An INTENT(IN) argument of the same type and kind type parameter as Y. If Y has the value zero, X must not have the value zero.

Result type and attributes

Same as X.

Result value

• It is expressed in radians and has a value equal to the principal value of the argument of the complex number (X, Y).
• It is in the range -PI < ATAN2(Y, X) ≤ PI.
• If X ≠ 0, the result approximates arctan(Y/X).
• If Y > 0, the result is positive.
• If Y < 0, the result is negative.
• If X = 0, the absolute value of the result is PI/2.

The -qxlf2003=signdzerointr option controls whether you get Fortran 2003 behavior. See qxlf2003

• If Y = 0 and X < 0, the result is PI.
• If Y = 0 and X > 0, the result is zero.

• If Y = 0 and X < 0, the result is PI if Y is positive real zero and -PI if Y is negative real zero.
• If Y = 0 and X > 0, the result is Y.