v?Atan2pi

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 4/28/2026

Version

Public

Computes the four-quadrant inverse tangent of the ratios of the corresponding elements of two vectors divided by π .

call vsatan2pi ( n , a , b , y )

call vsatan2pii(n, a, inca, b, incb, y, incy)

call vmsatan2pi ( n , a , b , y , mode )

call vmsatan2pii(n, a, inca, b, incb, y, incy, mode)

call vdatan2pi ( n , a , b , y )

call vdatan2pii(n, a, inca, b, incb, y, incy)

call vmdatan2pi ( n , a , b , y , mode )

call vmdatan2pii(n, a, inca, b, incb, y, incy, mode)

Name	Type	Description
`n`	INTEGER	Specifies the number of elements to be calculated.
`a` , `b`	REAL for `vsatan2pi` REAL for `vmsatan2pi` DOUBLE PRECISION for `vdatan2pi` DOUBLE PRECISION for `vmdatan2pi`	Pointers to the arrays containing 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)	Overrides the 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`	REAL for `vsatan2pi` REAL for `vmsatan2pi` DOUBLE PRECISION for `vdatan2pi` DOUBLE PRECISION for `vmdatan2pi`	Pointer to an array containing the output vector `y` .

The v?Atan2pi function computes the four-quadrant inverse tangent of the ratios of the corresponding elements of two vectors divided by π .

For the elements of the output vector y , the function computers the four-quadrant arctangent of a_i / b_i , with the result divided by π .

Special values for Real Function v?Atan2pi(x, y)

Argument 1	Argument 2	Result	Exception
∞	∞	-3/4
∞	`x` < +0	-1/2
∞	-0	+1/2
∞	+0	-1/2
∞	`x` > +0	-1/2
∞	∞	-1/4
`x` < +0	∞	-1
`x` < +0	-0	-1/2
`x` < +0	+0	-1/2
`x` < +0	∞	-0
-0	∞	-1
-0	`x` < +0	-1
-0	-0	-1
-0	+0	-0
-0	`x` > +0	-0
-0	∞	-0
+0	∞	+1
+0	`x` < +0	+1
+0	-0	+1
+0	+0	+0
+0	`x` > +0	+0
+0	∞	+0
`x` > +0	∞	+1
`x` > +0	-0	+1/2
`x` > +0	+0	+1/2
`x` > +0	∞	+1/4
∞	∞	+3/4
∞	`x` < +0	+1/2
∞	-0	+1/2
∞	+0	+1/2
∞	`x` > +0	+1/2
∞	∞	+1/4
`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

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