Language Reference

ATAN2(Y, X)

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.

Y

must be of type real.

X

must be of the same type and kind type parameter as Y. If Y has the value zero, X must not have the value zero.

Class

Elemental function

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 Y = 0 and X > 0, the result is zero.
• If Y = 0 and X < 0, the result is &pi..
• If X = 0, the absolute value of the result is &pi./2.

Examples

ATAN2 (1.5574077, 1.0) has the value 1.0.

Given that:

Y = |  1   1 |        X = | -1  1 |
    | -1  -1 |            | -1  1 |

the value of ATAN2(Y,X) is approximately:

ATAN2 (Y, X) = |  3&pi./4   &pi./4 |
               | -3&pi./4  -&pi./4 |

Notes:

1. IBM Extension.