v?Atan2

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 4/28/2026

Version

Public

vsAtan2 vdAtan2 vmsAtan2 vmdAtan2 Computes four-quadrant inverse tangent of elements of two vectors.

call vsatan2 ( n , a , b , y )

call vsatan2i(n, a, inca, b, incb, y, incy)

call vmsatan2 ( n , a , b , y , mode )

call vmsatan2i(n, a, inca, b, incb, y, incy, mode)

call vdatan2 ( n , a , b , y )

call vdatan2i(n, a, inca, b, incb, y, incy)

call vmdatan2 ( n , a , b , y , mode )

call vmdatan2i(n, a, inca, b, incb, y, incy, mode)

Name	Type	Description
`n`	INTEGER , INTENT(IN)	Specifies the number of elements to be calculated.
`a` , `b`	Fortran 77: DOUBLE PRECISION for `vdatan2` , `vmdatan2`Fortran 90: REAL , INTENT(IN) for `vsatan2` , `vmsatan2`Fortran 90: DOUBLE PRECISION , INTENT(IN) for `vdatan2` , `vmdatan2`	Arrays that specify the input vectors `a` and `b` .
`inca` , `incb` , `incy`	INTEGER, INTENT(IN)	Specifies increments for the elements of `a` , `b` and `y` .
`mode`	INTEGER(KIND=8) , INTENT(IN)	Overrides global VM mode setting for this function call. See vmlSetMode (Sets a new mode for VM functions according to the mode parameter and stores the previous VM mode to oldmode.) for possible values and their description.

Name	Type	Description
`y`	Fortran 90: DOUBLE PRECISION for `vdatan2` , `vmdatan2`Fortran 90: REAL , INTENT(OUT) for `vsatan2` , `vmsatan2`Fortran 90: DOUBLE PRECISION , INTENT(OUT) for `vdatan2` , `vmdatan2`	Array that specifies the output vector `y` .

The v?Atan2 function computes four-quadrant inverse tangent of elements of two vectors.

The elements of the output vector y are computed as the four-quadrant arctangent of a[i] / b[i] .

Special values for Real Function v?Atan2(x)

Argument 1	Argument 2	Result	Exception
∞	∞	-3* `π` /4
∞	X < +0	`π` /2
∞	-0	`π` /2
∞	+0	`π` /2
∞	X > +0	`π` /2
∞	∞	`π` /4
X < +0	∞	`π`
X < +0	-0	`π` /2
X < +0	+0	`π` /2
X < +0	∞	-0
-0	∞	`π`
-0	X < +0	`π`
-0	-0	`π`
-0	+0	-0
-0	X > +0	-0
-0	∞	-0
+0	∞	`π`
+0	X < +0	`π`
+0	-0	`π`
+0	+0	+0
+0	X > +0	+0
+0	∞	+0
X > +0	∞	`π`
X > +0	-0	`π` /2
X > +0	+0	`π` /2
X > +0	∞	+0
∞	∞	+3* `π` /4
∞	X < +0	`π` /2
∞	-0	`π` /2
∞	+0	`π` /2
∞	X > +0	`π` /2
∞	∞	`π` /4
X > +0	QNAN	QNAN
X > +0	SNAN	QNAN	INVALID
QNAN	X > +0	QNAN
SNAN	X > +0	QNAN	INVALID
QNAN	QNAN	QNAN
QNAN	SNAN	QNAN	INVALID
SNAN	QNAN	QNAN	INVALID
SNAN	SNAN	QNAN	INVALID