SpectraRust/src/synspec/math/opacon.rs

//! Continuous opacity, emissivity, and scattering coefficients.
//!
//! Translated from SYNSPEC54.FOR subroutine OPACON(ID,CROSS,ABSOC,EMISC,SCATC)
//! at line 12661.
//!
//! Computes absorption, emission, and scattering coefficients at a given
//! depth point for continuum frequencies.

use super::dwnfr1::{dwnfr1, Dwnfr1Params};
use super::gfree::gfree;
use super::sffhmi::sffhmi;

/// Parameters for continuous opacity calculation.
pub struct OpaconParams<'a> {
    /// Depth index
    pub id: usize,
    /// Temperature at each depth (K)
    pub temp: &'a [f64],
    /// Electron density at each depth (cm^-3)
    pub elec: &'a [f64],
    /// Continuum frequencies
    pub freqc: &'a [f64],
    /// Number of continuum frequencies
    pub nfreqc: usize,
    /// Number of ions
    pub nion: usize,
    /// First level index for each ion
    pub nfirst: &'a [usize],
    /// Last level index for each ion
    pub nlast: &'a [usize],
    /// Next ion index for each ion
    pub nnext: &'a [usize],
    /// Free-free flag for each ion
    pub ifree: &'a [i32],
    /// IELHM index (H- element)
    pub ielhm: usize,
    /// Ionic charge for each element
    pub iz: &'a [i32],
    /// Element index for each level
    pub iel: &'a [usize],
    /// Occupation probability flag for each level
    pub ifwop: &'a [i32],
    /// Population of each level at current depth
    pub popul_lev: &'a [f64],
    /// Statistical weight of each level
    pub g: &'a [f64],
    /// Ionization energy of each level (erg)
    pub enion: &'a [f64],
    /// Occupation probability for each level
    pub wop: &'a [f64],
    /// Dissolved fraction frequency for each level
    pub fropc: &'a [f64],
    /// Dissolved fraction index for each level
    pub indexp: &'a [i32],
    /// Z3 array for dissolved fraction
    pub z3: &'a [f64],
    /// ELEC23 array for dissolved fraction
    pub elec23: &'a [f64],
    /// DWC1 array for dissolved fraction
    pub dwc1: &'a [f64],
    /// DWC2 array for dissolved fraction
    pub dwc2: &'a [f64],
    /// DWC1 number of depth points
    pub ndepth: usize,
    /// Bergmann factor
    pub bergfc: f64,
    /// Planck function constant
    pub bn: f64,
    /// h/k constant
    pub hk: f64,
    /// Electron scattering cross-section
    pub sige: f64,
    /// Stimulated emission correction at current depth
    pub stim: f64,
    /// Planck function at current depth
    pub plan: f64,
    /// Photoionization cross-sections (nion x nfreqc)
    pub cross: &'a [&'a [f64]],
    /// Saha-Boltzmann factors for merged levels
    pub sgmerg_fn: Option<Box<dyn Fn(usize, usize, f64) -> f64>>,
    /// Additional opacity function
    pub opadd_fn: Option<Box<dyn Fn(usize, f64) -> (f64, f64, f64)>>,
    /// Lyman line function
    pub lymlin_fn: Option<Box<dyn Fn(usize, f64) -> (f64, f64, f64)>>,
    /// Photoionization function
    pub phtion_fn: Option<Box<dyn Fn(usize, &mut [f64], &mut [f64], &[f64], usize)>>,
    /// Photoionization function (extended)
    pub phtx_fn: Option<Box<dyn Fn(usize, &mut [f64], &mut [f64], &[f64], i32)>>,
}

/// Result of continuous opacity calculation.
pub struct OpaconResult {
    /// Absorption coefficient array
    pub absoc: Vec<f64>,
    /// Emission coefficient array
    pub emisc: Vec<f64>,
    /// Scattering coefficient array
    pub scatc: Vec<f64>,
}

/// Continuous opacity, emissivity, and scattering coefficients.
///
/// Computes absorption, emission, and scattering coefficients at a given
/// depth point for continuum frequencies. Includes bound-free, free-free,
/// and additional opacity contributions.
///
/// # Arguments
/// * `params` - Calculation parameters
///
/// # Returns
/// Arrays of absorption, emission, and scattering coefficients.
pub fn opacon(params: &OpaconParams) -> OpaconResult {
    let id = params.id;
    let t = params.temp[id];
    let ane = params.elec[id];
    let t1 = 1.0 / t;
    let hkt = params.hk * t1;
    let tk = hkt / params.bn;
    let srt = 1.0 / t.sqrt();
    let sgff = 3.694e8 * srt;
    let con = 2.0706e-16 * t1 * srt;
    let sce = ane * params.sige;

    let mut absoc = vec![0.0; params.nfreqc];
    let mut emisc = vec![0.0; params.nfreqc];
    let mut scatc = vec![0.0; params.nfreqc];

    for ij in 0..params.nfreqc {
        let fr = params.freqc[ij];
        let fr15 = fr * 1e-15;
        let bnu = params.bn * fr15 * fr15 * fr15;
        let hkf = hkt * fr;
        let mut abf = 0.0;
        let mut ebf = 0.0;
        let mut aff = 0.0;

        for il in 0..params.nion {
            let n0i = params.nfirst[il];
            let n1i = params.nlast[il];
            let nke = params.nnext[il];
            let xn = params.popul_lev[nke];

            // Bound-free contribution
            for ii in n0i..=n1i {
                let mut sg = 0.0;
                if params.ifwop[ii] < 0 {
                    // Merged level
                    if let Some(ref f) = params.sgmerg_fn {
                        sg = f(ii, id, fr);
                    }
                } else {
                    sg = params.cross[il][ij];
                    if sg <= 0.0 {
                        continue;
                    }
                    // Dissolved fraction correction
                    if params.indexp[ii] == 5 {
                        let izz = params.iz[params.iel[ii]] as usize;
                        let fr0 = params.enion[ii] / 6.6256e-27;
                        let dw1 = dwnfr1(&Dwnfr1Params {
                            fr,
                            fr0,
                            id,
                            izz,
                            z3: params.z3,
                            elec23: params.elec23,
                            dwc1: params.dwc1,
                            ndepth: params.ndepth,
                            dwc2: params.dwc2,
                            bergfc: params.bergfc,
                        });
                        sg *= dw1;
                    }
                }
                if params.popul_lev[ii] < 1e-20 || xn < 1e-20 {
                    continue;
                }
                abf += sg * params.popul_lev[ii];
                let xx = sg * xn * (params.enion[ii] * tk - hkf).exp() * params.wop[ii];
                let _ee = (params.enion[ii] * tk - hkf).exp();
                ebf += xx * con * params.g[ii] / params.g[nke];
            }

            let it = params.ifree[il];
            if it == 0 {
                continue;
            }

            // Free-free contribution
            let ie = il;
            if ie == params.ielhm {
                let sff = sffhmi(xn, fr, t);
                aff += sff;
            } else {
                let ch = params.iz[il] as f64 * params.iz[il] as f64;
                let sf1 = ch * xn * sgff / (fr * fr * fr);
                let sff = if it == 2 {
                    let sg = gfree(t, fr / ch);
                    sf1 * sg
                } else {
                    sf1
                };
                aff += sff;
            }
        }

        // Additional opacities
        let (abad, emad, scad) = if let Some(ref f) = params.opadd_fn {
            f(id, fr)
        } else {
            (0.0, 0.0, 0.0)
        };

        // Lyman lines
        let (ably, emly, scly) = if let Some(ref f) = params.lymlin_fn {
            f(id, fr)
        } else {
            (0.0, 0.0, 0.0)
        };

        // Total opacity and emissivity
        let x = (-hkf).exp();
        let x1 = 1.0 - x;
        let bne = bnu * x * ane;
        absoc[ij] = abf + ane * (x1 * aff - ebf) + abad + ably;
        emisc[ij] = bne * aff + bnu * ane * ebf + emad + emly;
        scatc[ij] = scad + scly + sce;
    }

    // Photoionization contributions
    if let Some(ref f) = params.phtion_fn {
        f(id, &mut absoc, &mut emisc, params.freqc, params.nfreqc);
    }
    if let Some(ref f) = params.phtx_fn {
        f(id, &mut absoc, &mut emisc, params.freqc, 1);
    }

    OpaconResult {
        absoc,
        emisc,
        scatc,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_opacon_basic() {
        let temp = [10000.0];
        let elec = [1e13];
        let freqc = [1e14, 2e14, 3e14];
        let nfirst = [0];
        let nlast = [0];
        let nnext = [1];
        let ifree = [1];
        let iz = [1];
        let iel = [0];
        let ifwop = [1];
        let popul_lev = [1e12, 1e10];
        let g = [1.0, 2.0];
        let enion = [0.0, 1e-11];
        let wop = [1.0, 1.0];
        let fropc = [0.0, 0.0];
        let indexp = [0, 0];
        let z3 = [1.0];
        let elec23 = [2.15e-9];
        let dwc1 = [0.0];
        let dwc2 = [0.0];
        let cross_row: &[f64] = &[1e-18, 2e-18, 3e-18];
        let cross: &[&[f64]] = &[cross_row];

        let params = OpaconParams {
            id: 0,
            temp: &temp,
            elec: &elec,
            freqc: &freqc,
            nfreqc: 3,
            nion: 1,
            nfirst: &nfirst,
            nlast: &nlast,
            nnext: &nnext,
            ifree: &ifree,
            ielhm: 99,
            iz: &iz,
            iel: &iel,
            ifwop: &ifwop,
            popul_lev: &popul_lev,
            g: &g,
            enion: &enion,
            wop: &wop,
            fropc: &fropc,
            indexp: &indexp,
            z3: &z3,
            elec23: &elec23,
            dwc1: &dwc1,
            dwc2: &dwc2,
            ndepth: 1,
            bergfc: 1.0,
            bn: 1.0,
            hk: 4.79928144e-11,
            sige: 6.65e-25,
            stim: 1.0,
            plan: 1.0,
            cross,
            sgmerg_fn: None,
            opadd_fn: None,
            lymlin_fn: None,
            phtion_fn: None,
            phtx_fn: None,
        };

        let result = opacon(&params);
        assert_eq!(result.absoc.len(), 3);
        assert_eq!(result.emisc.len(), 3);
        assert_eq!(result.scatc.len(), 3);
        assert!(result.absoc[0].is_finite());
        assert!(result.scatc[0].is_finite());
    }
}