Embedded Software and Motor Control Libraries for PXR40xx

Table 4-42. GFLIB_Atan_FLT arguments
(continued)
Type Name Direction Description
const
GFLIB_ATAN_T_FLT
*const
4.33.3 Return
pParam input Pointer to an array of rational polynomial coefficients.
The function returns the atan of the input argument as a single precision floating point
number that contains the angle in radians between (- π/2, π/2).
4.33.4 Description
The GFLIB_Atan_FLT function provides a computational method for the calculation of a
standard trigonometric arctangent function arctan(x), using the rational polynomial
approximation. Function arctan(x) takes a ratio and returns the angle of two sides of a
right-angled triangle. The ratio is the length of the side opposite the angle divided by the
length of the side adjacent to the angle. The graph of arctan(x) is shown in Figure 4-23.
Figure 4-23. Course of the function GFLIB_Atan
Chapter 4 API References
As can be observed from Figure 4-23, the value of the arctan(x) function for interval (- ∞,
0) is identical, but with the opposite sign, to the output of the function for [0, ∞).
Therefore, the approximation of the arctangent function over the entire defined range of
input values can be simplified to the approximation for a ratio in the range [0, ∞), and
then, depending on the input sign, the result will be negated.
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Freescale Semiconductor, Inc. 243