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primitive_float_agm

Function primitive_float_agm 

Source
pub fn primitive_float_agm<T>(x: T, y: T) -> T
where Float: From<T> + PartialOrd<T>, for<'a> T: ExactFrom<&'a Float> + RoundingFrom<&'a Float> + PrimitiveFloat,
Expand description

Computes the arithmetic-geometric mean (AGM) of two primitive floats.

$$ f(x,y) = \text{AGM}(x,y)+\varepsilon =\frac{\pi}{2}\left(\int_0^{\frac{\pi}{2}}\frac{\mathrm{d}\theta} {\sqrt{x^2\cos^2\theta+y^2\sin^2\theta}}\right)^{-1}+\varepsilon. $$

  • If $\text{AGM}(x,y)$ is infinite, zero, or NaN, $\varepsilon$ may be ignored or assumed to be 0.
  • If $\text{AGM}(x,y)$ is finite and nonzero, then $|\varepsilon| < 2^{\lfloor\log_2 \text{AGM}(x,y)\rfloor-p}$, where $p$ is precision of the output (typically 24 if T is a f32 and 53 if T is a f64, but less if the output is subnormal).

Special cases:

  • $f(\text{NaN},x)=f(x,\text{NaN})=f(-\infty,x)=f(x,-\infty)=\text{NaN}$
  • $f(\infty,x)=f(x,\infty)=\text{NaN}$ if $x\neq\infty$
  • $f(\infty,\infty)=\infty$
  • $f(\pm0.0,x)=f(x,\pm0.0)=0.0$
  • $f(x,y)=\text{NaN}$ if $x<0$ or $y<0$

§Worst-case complexity

Constant time and additional memory.

§Examples

use malachite_base::num::float::NiceFloat;
use malachite_float::arithmetic::agm::primitive_float_agm;

assert_eq!(
    NiceFloat(primitive_float_agm(24.0, 6.0)),
    NiceFloat(13.458171481725616)
);