Function observed_frequency_longitudinal 

pub fn observed_frequency_longitudinal(
    emitted_frequency: f64,
    beta: f64,
) -> Option<f64>

Computes observed longitudinal Doppler-shifted frequency f_observed = f_emitted * D.

Positive beta means the source is approaching the observer.

Returns None when emitted_frequency is negative or not finite, when beta is invalid, or when the computed frequency is not finite.

Examples

use use_relativity::observed_frequency_longitudinal;

assert!((observed_frequency_longitudinal(100.0, 0.6).unwrap() - 200.0).abs() < 1.0e-12);