limma-rust 0.1.0

//! `arrayWeights` — estimate array quality weights.
//!
//! Pure-Rust port of limma's `arrayWeights` and its internal estimators for the
//! log-linear array-variance model `log(sigma_array^2) = Z gamma`, with array
//! weights `w = exp(-Z2 gamma)`:
//!
//! * [`array_weights`] — `.arrayWeightsREML`, the default path (`method="auto"`
//!   with no observation weights and no missing values resolves to `"reml"`):
//!   an exact Fisher-scoring REML similar to `statmod::remlscor`.
//! * [`array_weights_gene_by_gene`] — `.arrayWeightsGeneByGene`, a single
//!   forward Newton pass used for `method="genebygene"` (and `method="auto"`
//!   when observation weights or `NA`s are present).
//! * [`array_weights_prwts_reml`] — `.arrayWeightsPrWtsREML`, the per-gene REML
//!   variant selected by `method="reml"` when observation weights are present.
//! * [`array_weights_quick`] — `arrayWeightsQuick`, a fast approximation from an
//!   already-fitted model.

use ndarray::{Array1, Array2, Axis};

use crate::fit::MArrayLM;
use crate::linalg::{qr_econ, solve_upper};

/// `contr.sum(n)`: an `n x (n-1)` contrast matrix whose columns sum to zero —
/// an identity block on top of a final row of `-1`s.
pub(crate) fn contr_sum(n: usize) -> Array2<f64> {
    let mut z = Array2::<f64>::zeros((n, n - 1));
    for j in 0..(n - 1) {
        z[[j, j]] = 1.0;
        z[[n - 1, j]] = -1.0;
    }
    z
}

/// Solve a small general linear system `a x = b` by Gaussian elimination with
/// partial pivoting (`a` is `k x k`). Used for the `ngam x ngam` Fisher-scoring
/// step, mirroring R's `solve(info2, dl)`.
pub(crate) fn solve_linear(a: &Array2<f64>, b: &Array1<f64>) -> Array1<f64> {
    let k = a.nrows();
    let mut m = a.clone();
    let mut rhs = b.clone();
    for col in 0..k {
        let mut piv = col;
        let mut best = m[[col, col]].abs();
        for r in (col + 1)..k {
            let v = m[[r, col]].abs();
            if v > best {
                best = v;
                piv = r;
            }
        }
        if piv != col {
            for c in 0..k {
                let tmp = m[[col, c]];
                m[[col, c]] = m[[piv, c]];
                m[[piv, c]] = tmp;
            }
            rhs.swap(col, piv);
        }
        let d = m[[col, col]];
        for r in (col + 1)..k {
            let f = m[[r, col]] / d;
            if f != 0.0 {
                for c in col..k {
                    let v = m[[col, c]];
                    m[[r, c]] -= f * v;
                }
                rhs[r] -= f * rhs[col];
            }
        }
    }
    let mut x = Array1::<f64>::zeros(k);
    for i in (0..k).rev() {
        let mut sum = rhs[i];
        for j in (i + 1)..k {
            sum -= m[[i, j]] * x[j];
        }
        x[i] = sum / m[[i, i]];
    }
    x
}

/// Estimate array quality weights by REML.
///
/// * `exprs` — `ngenes x narrays` expression matrix (no `NA`/infinite values).
/// * `design` — `narrays x p` design matrix (assumed full column rank).
/// * `var_design` — optional `narrays x ngam` variance design `Z2` whose columns
///   sum to zero; defaults to `contr.sum(narrays)`.
/// * `prior_n` — prior support pulling weights toward 1 (limma default `10`).
/// * `maxiter`, `tol` — Fisher-scoring controls (limma defaults `50`, `1e-5`).
///
/// Returns a length-`narrays` vector of array weights. Matches
/// `limma::arrayWeights(exprs, design)` on data with no weights and no `NA`s.
pub fn array_weights(
    exprs: &Array2<f64>,
    design: &Array2<f64>,
    var_design: Option<&Array2<f64>>,
    prior_n: f64,
    maxiter: usize,
    tol: f64,
) -> Array1<f64> {
    let narrays = exprs.ncols();
    let ngenes_all = exprs.nrows();
    let p = design.ncols();

    let mut w = Array1::<f64>::ones(narrays);
    // Need >=2 genes and >=2 residual df for useful estimates.
    if ngenes_all < 2 || narrays < p + 2 {
        return w;
    }

    let z2 = match var_design {
        Some(v) => v.to_owned(),
        None => contr_sum(narrays),
    };
    let ngam = z2.ncols();
    let nz = ngam + 1;

    // Z = [1 | Z2].
    let mut zmat = Array2::<f64>::ones((narrays, nz));
    for j in 0..ngam {
        for i in 0..narrays {
            zmat[[i, j + 1]] = z2[[i, j]];
        }
    }
    let z2tz2 = z2.t().dot(&z2);
    let dfres = (narrays - p) as f64;

    // Initial unweighted fit: drop genes with no residual variance.
    let (q0, _r0) = qr_econ(design);
    let mut kept: Vec<usize> = Vec::with_capacity(ngenes_all);
    for g in 0..ngenes_all {
        let yg = exprs.row(g).to_owned();
        let cg = q0.t().dot(&yg);
        let s2 = (yg.dot(&yg) - cg.dot(&cg)) / dfres;
        if s2 >= 1e-15 {
            kept.push(g);
        }
    }
    if kept.len() < 2 {
        return w;
    }
    let y = exprs.select(Axis(0), &kept);
    let ngenes = y.nrows();
    let ngenes_f = ngenes as f64;

    let mut gam = Array1::<f64>::zeros(ngam);
    let mut convcrit_last = f64::INFINITY;
    let p2 = p * (p + 1) / 2;

    for _iter in 1..=maxiter {
        let sw: Array1<f64> = w.mapv(f64::sqrt);

        // Weighted design Xw = diag(sqrt(w)) * design, then its QR.
        let mut xw = design.clone();
        for i in 0..narrays {
            for j in 0..p {
                xw[[i, j]] *= sw[i];
            }
        }
        let (qe, r) = qr_econ(&xw);

        // Per-gene raw residuals and residual variances s2.
        let mut resid = Array2::<f64>::zeros((narrays, ngenes));
        let mut s2 = Array1::<f64>::zeros(ngenes);
        for gi in 0..ngenes {
            let yg = y.row(gi).to_owned();
            let ywg = &yg * &sw;
            let cg = qe.t().dot(&ywg);
            let beta = solve_upper(&r, &cg);
            let fitted = design.dot(&beta);
            let ss = ywg.dot(&ywg) - cg.dot(&cg);
            s2[gi] = ss / dfres;
            for i in 0..narrays {
                resid[[i, gi]] = yg[i] - fitted[i];
            }
        }

        // Half-vectorised hat-matrix machinery: Q2 (narrays x p2) and leverages h.
        // Columns 0..p hold the squared terms Q[,a]^2 (their row sum is the
        // leverage); columns p..p2 hold sqrt(2)-scaled cross products so that
        // (Q2 Q2^T)[i,j] = ((QQ^T)[i,j])^2.
        let mut q2 = Array2::<f64>::zeros((narrays, p2));
        let mut h = Array1::<f64>::zeros(narrays);
        for i in 0..narrays {
            let mut col = 0usize;
            for k in 0..p {
                for a in 0..(p - k) {
                    q2[[i, col]] = qe[[i, a]] * qe[[i, a + k]];
                    col += 1;
                }
            }
            for c in p..p2 {
                q2[[i, c]] *= std::f64::consts::SQRT_2;
            }
            let mut lev = 0.0;
            for c in 0..p {
                lev += q2[[i, c]];
            }
            h[i] = lev;
        }

        // info = Z' diag(1-2h) Z + (Q2'Z)'(Q2'Z).
        let mut info = Array2::<f64>::zeros((nz, nz));
        for a in 0..nz {
            for b in 0..nz {
                let mut acc = 0.0;
                for i in 0..narrays {
                    acc += zmat[[i, a]] * (1.0 - 2.0 * h[i]) * zmat[[i, b]];
                }
                info[[a, b]] = acc;
            }
        }
        let q2tz = q2.t().dot(&zmat);
        let gram = q2tz.t().dot(&q2tz);
        info = &info + &gram;

        // Fisher information for gam: Schur complement removing the intercept.
        let i00 = info[[0, 0]];
        let mut info2 = Array2::<f64>::zeros((ngam, ngam));
        for a in 0..ngam {
            for b in 0..ngam {
                info2[[a, b]] = info[[a + 1, b + 1]] - info[[a + 1, 0]] * info[[0, b + 1]] / i00;
            }
        }

        // Score: z[i] = mean_g(w[i] resid[i,g]^2 / s2_g) - (1 - h[i]).
        let mut zvec = Array1::<f64>::zeros(narrays);
        for i in 0..narrays {
            let mut acc = 0.0;
            for gi in 0..ngenes {
                acc += w[i] * resid[[i, gi]] * resid[[i, gi]] / s2[gi];
            }
            zvec[i] = acc / ngenes_f - (1.0 - h[i]);
        }

        // Prior support for w=1 / gam=0.
        for a in 0..ngam {
            for b in 0..ngam {
                info2[[a, b]] = ngenes_f * info2[[a, b]] + prior_n * z2tz2[[a, b]];
            }
        }
        for i in 0..narrays {
            zvec[i] = ngenes_f * zvec[i] + prior_n * (w[i] - 1.0);
        }

        // Fisher scoring step.
        let dl = z2.t().dot(&zvec);
        let gamstep = solve_linear(&info2, &dl);
        let convcrit = dl.dot(&gamstep) / (ngam as f64) / (ngenes_f + prior_n);
        if convcrit.is_nan() || convcrit >= convcrit_last {
            break;
        }
        convcrit_last = convcrit;

        gam = &gam + &gamstep;
        w = z2.dot(&gam).mapv(|x| (-x).exp());

        if convcrit < tol {
            break;
        }
    }

    w
}

/// Estimate array quality weights by REML with per-observation prior weights
/// (`.arrayWeightsPrWtsREML`).
///
/// The prior-weighted analogue of [`array_weights`]: because each gene carries
/// its own observation weights, the weighted design (and hence its QR) differs
/// per gene, so the Fisher information and score are accumulated gene-by-gene
/// rather than computed once and scaled by `ngenes`. limma reaches this routine
/// from `arrayWeights(..., weights=W, method="reml")` (the `"auto"` method sends
/// weighted data to gene-by-gene instead).
///
/// Every QR-sign-dependent term enters only through squares or `crossprod`
/// forms, so the result is independent of the QR column signs and matches R.
///
/// * `exprs` — `ngenes x narrays` expression matrix (no `NA`/infinite values).
/// * `design` — `narrays x p` design matrix (assumed full column rank).
/// * `weights` — `ngenes x narrays` positive observation weights.
/// * `var_design` — optional `narrays x ngam` variance design `Z2` whose columns
///   sum to zero; defaults to `contr.sum(narrays)`.
/// * `prior_n` — prior support pulling weights toward 1 (limma default `10`).
/// * `maxiter`, `tol` — Fisher-scoring controls (`arrayWeights` defaults `50`,
///   `1e-5`).
///
/// Returns a length-`narrays` vector of array weights.
pub fn array_weights_prwts_reml(
    exprs: &Array2<f64>,
    design: &Array2<f64>,
    weights: &Array2<f64>,
    var_design: Option<&Array2<f64>>,
    prior_n: f64,
    maxiter: usize,
    tol: f64,
) -> Array1<f64> {
    let narrays = exprs.ncols();
    let ngenes = exprs.nrows();
    let p = design.ncols();

    let z2 = match var_design {
        Some(v) => v.to_owned(),
        None => contr_sum(narrays),
    };
    let ngam = z2.ncols();
    let nz = ngam + 1;

    // Z = [1 | Z2].
    let mut zmat = Array2::<f64>::ones((narrays, nz));
    for j in 0..ngam {
        for i in 0..narrays {
            zmat[[i, j + 1]] = z2[[i, j]];
        }
    }
    let z2tz2 = z2.t().dot(&z2);
    let dfres = (narrays - p) as f64;
    let denom = ngenes as f64 + prior_n;
    let p2 = p * (p + 1) / 2;

    let mut gam = Array1::<f64>::zeros(ngam);
    let mut w = Array1::<f64>::ones(narrays);

    for _iter in 1..=maxiter {
        // Start info2 and score z from the prior support for w=1 / gam=0.
        let mut info2 = z2tz2.mapv(|x| x * prior_n);
        let mut zvec = w.mapv(|wi| prior_n * (wi - 1.0));

        for g in 0..ngenes {
            // Combined per-array weight w * weights[g,], then weighted LS fit.
            let cw: Vec<f64> = (0..narrays).map(|i| w[i] * weights[[g, i]]).collect();
            let sw: Vec<f64> = cw.iter().map(|&v| v.sqrt()).collect();
            let mut xw = design.clone();
            for i in 0..narrays {
                for j in 0..p {
                    xw[[i, j]] *= sw[i];
                }
            }
            let yg = exprs.row(g);
            let yw: Array1<f64> = (0..narrays).map(|i| yg[i] * sw[i]).collect();
            let (qe, r) = qr_econ(&xw);
            let cg = qe.t().dot(&yw);
            let beta = solve_upper(&r, &cg);
            let fitted = design.dot(&beta);
            let resid: Vec<f64> = (0..narrays).map(|i| yg[i] - fitted[i]).collect();
            let s2 = (yw.dot(&yw) - cg.dot(&cg)) / dfres;

            // Half-vectorised hat machinery for this gene: Q2 (narrays x p2)
            // and leverages h, exactly as in `array_weights`.
            let mut q2 = Array2::<f64>::zeros((narrays, p2));
            let mut h = vec![0.0f64; narrays];
            for i in 0..narrays {
                let mut col = 0usize;
                for k in 0..p {
                    for a in 0..(p - k) {
                        q2[[i, col]] = qe[[i, a]] * qe[[i, a + k]];
                        col += 1;
                    }
                }
                for c in p..p2 {
                    q2[[i, c]] *= std::f64::consts::SQRT_2;
                }
                let mut lev = 0.0;
                for c in 0..p {
                    lev += q2[[i, c]];
                }
                h[i] = lev;
            }

            // info = Z' diag(1-2h) Z + (Q2'Z)'(Q2'Z).
            let mut info = Array2::<f64>::zeros((nz, nz));
            for a in 0..nz {
                for b in 0..nz {
                    let mut acc = 0.0;
                    for i in 0..narrays {
                        acc += zmat[[i, a]] * (1.0 - 2.0 * h[i]) * zmat[[i, b]];
                    }
                    info[[a, b]] = acc;
                }
            }
            let q2tz = q2.t().dot(&zmat);
            let gram = q2tz.t().dot(&q2tz);
            info = &info + &gram;

            // Accumulate the intercept-removing Schur complement (every gene).
            let i00 = info[[0, 0]];
            for a in 0..ngam {
                for b in 0..ngam {
                    info2[[a, b]] +=
                        info[[a + 1, b + 1]] - info[[a + 1, 0]] * info[[0, b + 1]] / i00;
                }
            }

            // Score residual term, skipped for genes with no residual variance.
            if s2 > 1e-15 {
                for i in 0..narrays {
                    zvec[i] += cw[i] * resid[i] * resid[i] / s2 - (1.0 - h[i]);
                }
            }
        }

        // Average information and score over genes plus prior support.
        info2.mapv_inplace(|x| x / denom);
        zvec.mapv_inplace(|x| x / denom);

        // Fisher scoring step and weight update.
        let dl = z2.t().dot(&zvec);
        let gamstep = solve_linear(&info2, &dl);
        gam = &gam + &gamstep;
        w = z2.dot(&gam).mapv(|x| (-x).exp());

        let convcrit = dl.dot(&gamstep) / denom / (ngam as f64);
        if convcrit.is_nan() || convcrit < tol {
            break;
        }
    }

    w
}

/// Weighted least-squares residuals, leverages and residual variance for one
/// gene. Returns `(resid, lev, s2)` where `resid = y - X beta` are raw
/// residuals, `lev` the hat-matrix diagonals of the weighted design, and
/// `s2 = sum(w resid^2) / (n - p)` (`mean(effects[-(1:rank)]^2)` in `lm.wfit`).
pub(crate) fn wfit_resid_lev_s2(
    x: &Array2<f64>,
    y: &[f64],
    w: &[f64],
) -> (Vec<f64>, Vec<f64>, f64) {
    let n = x.nrows();
    let p = x.ncols();
    let sw: Vec<f64> = w.iter().map(|&v| v.sqrt()).collect();
    let mut xw = x.clone();
    for i in 0..n {
        for j in 0..p {
            xw[[i, j]] *= sw[i];
        }
    }
    let yw: Array1<f64> = (0..n).map(|i| y[i] * sw[i]).collect();
    let (qe, r) = qr_econ(&xw);
    let cg = qe.t().dot(&yw);
    let beta = solve_upper(&r, &cg);
    let fitted = x.dot(&beta);
    let resid: Vec<f64> = (0..n).map(|i| y[i] - fitted[i]).collect();
    let lev: Vec<f64> = (0..n)
        .map(|i| (0..p).map(|k| qe[[i, k]] * qe[[i, k]]).sum())
        .collect();
    let rss = yw.dot(&yw) - cg.dot(&cg);
    let s2 = rss / (n - p) as f64;
    (resid, lev, s2)
}

/// Estimate array quality weights by the gene-by-gene update algorithm
/// (`.arrayWeightsGeneByGene`).
///
/// A single forward pass over genes, each performing one Newton step of the
/// log-linear array-variance model `log(sigma_array^2) = Z2 gamma`, with array
/// weights `w = exp(-Z2 gamma)`. This is the path limma's `arrayWeights` takes
/// for `method = "genebygene"` (and for `method = "auto"` when observation
/// weights or missing values are present), and the estimator used inside
/// `voomWithQualityWeights`.
///
/// * `exprs` — `ngenes x narrays` expression matrix (`NaN` marks missing
///   observations, which are dropped per gene as in `lm.wfit`).
/// * `design` — `narrays x p` design matrix (assumed full column rank).
/// * `weights` — optional `ngenes x narrays` observation weights, multiplied
///   into the running array weights per gene.
/// * `var_design` — optional `narrays x ngam` variance design `Z2`; defaults to
///   `contr.sum(narrays)`.
/// * `prior_n` — prior support pulling weights toward 1 (limma default `10`).
///
/// Returns a length-`narrays` vector of array weights.
pub fn array_weights_gene_by_gene(
    exprs: &Array2<f64>,
    design: &Array2<f64>,
    weights: Option<&Array2<f64>>,
    var_design: Option<&Array2<f64>>,
    prior_n: f64,
) -> Array1<f64> {
    let ngenes = exprs.nrows();
    let narrays = exprs.ncols();
    let nparams = design.ncols();

    let z2 = match var_design {
        Some(v) => v.to_owned(),
        None => contr_sum(narrays),
    };
    let ngam = z2.ncols();
    let nz = ngam + 1;

    // Z = [1 | Z2].
    let mut zmat = Array2::<f64>::ones((narrays, nz));
    for j in 0..ngam {
        for i in 0..narrays {
            zmat[[i, j + 1]] = z2[[i, j]];
        }
    }

    let mut gam = Array1::<f64>::zeros(ngam);
    let mut aw = Array1::<f64>::ones(narrays);
    // info2 starts at prior.n * Z2'Z2 and accumulates a Schur complement per gene.
    let mut info2 = z2.t().dot(&z2);
    info2.mapv_inplace(|x| x * prior_n);

    for i in 0..ngenes {
        // w = aw, optionally scaled by this gene's observation weights.
        let mut w: Vec<f64> = aw.to_vec();
        if let Some(wt) = weights {
            for (j, wj) in w.iter_mut().enumerate() {
                *wj *= wt[[i, j]];
            }
        }
        let yrow: Vec<f64> = exprs.row(i).to_vec();

        let mut d = vec![0.0f64; narrays];
        let mut h1 = vec![0.0f64; narrays];
        let s2;
        if yrow.iter().any(|v| v.is_nan()) {
            let obs: Vec<usize> = (0..narrays).filter(|&j| yrow[j].is_finite()).collect();
            let nobs = obs.len();
            // Need >2 observations and >=2 residual df (nobs - rank).
            if nobs <= 2 || nobs < nparams + 2 {
                continue;
            }
            let mut xsub = Array2::<f64>::zeros((nobs, nparams));
            let mut ysub = vec![0.0f64; nobs];
            let mut wsub = vec![0.0f64; nobs];
            for (r, &j) in obs.iter().enumerate() {
                for c in 0..nparams {
                    xsub[[r, c]] = design[[j, c]];
                }
                ysub[r] = yrow[j];
                wsub[r] = w[j];
            }
            let (resid, lev, s2v) = wfit_resid_lev_s2(&xsub, &ysub, &wsub);
            s2 = s2v;
            for (r, &j) in obs.iter().enumerate() {
                d[j] = wsub[r] * resid[r] * resid[r];
                h1[j] = 1.0 - lev[r];
            }
        } else {
            let (resid, lev, s2v) = wfit_resid_lev_s2(design, &yrow, &w);
            s2 = s2v;
            for j in 0..narrays {
                d[j] = w[j] * resid[j] * resid[j];
                h1[j] = 1.0 - lev[j];
            }
        }
        if s2 < 1e-15 {
            continue;
        }

        // info = Z' diag(h1) Z, then accumulate the intercept-removing Schur
        // complement info[-1,-1] - info[-1,1] info[1,1]^-1 info[1,-1] into info2.
        let mut info = Array2::<f64>::zeros((nz, nz));
        for a in 0..nz {
            for b in 0..nz {
                let mut acc = 0.0;
                for j in 0..narrays {
                    acc += zmat[[j, a]] * h1[j] * zmat[[j, b]];
                }
                info[[a, b]] = acc;
            }
        }
        let i00 = info[[0, 0]];
        for a in 0..ngam {
            for b in 0..ngam {
                info2[[a, b]] += info[[a + 1, b + 1]] - info[[a + 1, 0]] * info[[0, b + 1]] / i00;
            }
        }

        // Newton step: gam += solve(info2, Z2' (d/s2 - h1)); aw = exp(-Z2 gam).
        let z: Array1<f64> = (0..narrays).map(|j| d[j] / s2 - h1[j]).collect();
        let dl = z2.t().dot(&z);
        let step = solve_linear(&info2, &dl);
        gam = &gam + &step;
        aw = z2.dot(&gam).mapv(|x| (-x).exp());
    }

    aw
}

/// `arrayWeightsQuick(y, fit)`: fast approximate array quality weights from an
/// already-fitted model.
///
/// For each array `j`, `w_j = 1 / mean_i( e_ij^2 / (s_i^2 (1 - h_j)) )` where
/// `e = y - coef %*% t(design)` are the residuals, `s_i = fit.sigma_i`, and
/// `h_j` is the leverage (hat-matrix diagonal) of design row `j`. Gene means
/// drop `NaN` ratios (`na.rm = TRUE`) but keep `Inf` ones, so a zero residual
/// variance drives the corresponding weight to 0 — matching limma's
/// `colMeans(..., na.rm = TRUE)`.
///
/// Panics if `fit.design` is `None`. Unlike limma this does not warn when the
/// fit carries observation weights (it likewise ignores them).
pub fn array_weights_quick(y: &Array2<f64>, fit: &MArrayLM) -> Array1<f64> {
    let design = fit
        .design
        .as_ref()
        .expect("arrayWeightsQuick requires a design in the fit");
    let narrays = design.nrows();
    let ngenes = y.nrows();

    let fitted = fit.coefficients.dot(&design.t());
    // Leverages h_j = sum_k Q[j,k]^2 from the thin QR of the design.
    let (q, _r) = qr_econ(design);
    let h: Vec<f64> = (0..narrays)
        .map(|j| q.row(j).iter().map(|&v| v * v).sum::<f64>())
        .collect();

    let mut w = Array1::<f64>::zeros(narrays);
    for j in 0..narrays {
        let denom_j = 1.0 - h[j];
        let mut sum = 0.0;
        let mut cnt = 0usize;
        for i in 0..ngenes {
            let e = y[[i, j]] - fitted[[i, j]];
            let s2 = fit.sigma[i] * fit.sigma[i];
            let ratio = e * e / (s2 * denom_j);
            if !ratio.is_nan() {
                sum += ratio;
                cnt += 1;
            }
        }
        w[j] = cnt as f64 / sum;
    }
    w
}

#[cfg(test)]
#[allow(clippy::excessive_precision)]
mod tests {
    use super::*;
    use ndarray::array;

    /// Rebuild scratch/vwqw_ref.R's fixture A: a 12x6 heteroscedastic
    /// log-expression matrix and matching observation-weight matrix from the
    /// same 0-indexed rational formula, plus the `~group` design.
    fn gbg_fixture() -> (Array2<f64>, Array2<f64>, Array2<f64>) {
        let ngenes = 12usize;
        let narrays = 6usize;
        let grp = [0.0, 0.0, 0.0, 1.0, 1.0, 1.0];
        let scale = [0.5, 0.7, 1.0, 1.3, 1.6, 2.0];
        let mut e = Array2::<f64>::zeros((ngenes, narrays));
        let mut wt = Array2::<f64>::zeros((ngenes, narrays));
        for g in 0..ngenes {
            let gi = g as i64;
            for j in 0..narrays {
                let ji = j as i64;
                let noise = (((gi * 7 + ji * 5) % 11) - 5) as f64 * 0.1 * scale[j];
                e[[g, j]] = 5.0 + (gi % 5) as f64 * 0.5 + grp[j] * 0.3 + noise;
                wt[[g, j]] = 0.5 + ((gi * 3 + ji * 2) % 7) as f64 * 0.15;
            }
        }
        let mut design = Array2::<f64>::zeros((narrays, 2));
        for j in 0..narrays {
            design[[j, 0]] = 1.0;
            design[[j, 1]] = grp[j];
        }
        (e, design, wt)
    }

    #[test]
    fn array_weights_gene_by_gene_matches_r() {
        let (e, design, wt) = gbg_fixture();

        let aw = array_weights_gene_by_gene(&e, &design, None, None, 10.0);
        let want = [
            1.5261488797077414,
            1.200903015330324,
            1.2231111922725117,
            1.2216065418856867,
            0.42436321655995812,
            0.86051835803628207,
        ];
        for (g, x) in aw.iter().zip(want.iter()) {
            assert!((g - x).abs() < 1e-7, "no-weights: got {g}, want {x}");
        }

        let aww = array_weights_gene_by_gene(&e, &design, Some(&wt), None, 10.0);
        let want_w = [
            1.5273497496573842,
            1.1661798617674437,
            1.2204452025989252,
            1.2146290021966843,
            0.42565954641887849,
            0.8897574953263433,
        ];
        for (g, x) in aww.iter().zip(want_w.iter()) {
            assert!((g - x).abs() < 1e-7, "with-weights: got {g}, want {x}");
        }

        // NA path: blank gene 2 col 4, gene 6 col 0, gene 9 col 5 (0-indexed).
        let mut ena = e.clone();
        ena[[2, 4]] = f64::NAN;
        ena[[6, 0]] = f64::NAN;
        ena[[9, 5]] = f64::NAN;
        let awn = array_weights_gene_by_gene(&ena, &design, None, None, 10.0);
        let want_na = [
            1.4797107434846923,
            1.1254112099887159,
            1.1542363030943652,
            1.2058806596955525,
            0.47074236183939411,
            0.91649393378073563,
        ];
        for (g, x) in awn.iter().zip(want_na.iter()) {
            assert!((g - x).abs() < 1e-7, "NA: got {g}, want {x}");
        }
    }

    /// 12 genes x 6 arrays, deliberately heteroscedastic across arrays, with a
    /// two-group design (~group). Reference weights from limma 3.68.3:
    /// `arrayWeights(E, model.matrix(~group))`.
    #[test]
    fn array_weights_reml_matches_r() {
        let exprs = array![
            [4.871, 4.629, 4.697, 5.807, 4.798, 5.195],
            [6.356, 6.349, 6.764, 4.125, 3.125, 4.752],
            [4.298, 4.659, 4.508, 5.936, 4.075, 7.367],
            [8.896, 9.420, 8.915, 9.165, 9.466, 8.598],
            [6.563, 6.610, 6.813, 6.123, 6.155, 7.309],
            [4.443, 4.283, 3.851, 5.435, 5.304, 5.784],
            [7.247, 7.184, 7.620, 6.533, 7.878, 6.820],
            [7.456, 7.644, 8.368, 9.096, 7.422, 10.245],
            [7.229, 6.945, 6.986, 8.178, 7.445, 10.159],
            [5.378, 5.177, 4.919, 7.692, 6.023, 7.432],
            [8.748, 9.133, 9.280, 9.431, 10.394, 11.954],
            [6.697, 7.010, 6.719, 4.293, 3.114, 5.796],
        ];
        // model.matrix(~group), group = c(A,A,A,B,B,B).
        let design = array![
            [1.0, 0.0],
            [1.0, 0.0],
            [1.0, 0.0],
            [1.0, 1.0],
            [1.0, 1.0],
            [1.0, 1.0],
        ];
        let want = [
            1.611164881845,
            1.659781018122,
            1.455189349487,
            1.160250145839,
            0.462418787784,
            0.478963710208,
        ];

        let w = array_weights(&exprs, &design, None, 10.0, 50, 1e-5);
        assert_eq!(w.len(), want.len());
        for (got, exp) in w.iter().zip(want.iter()) {
            assert!(
                (got - exp).abs() < 1e-6,
                "array weight mismatch: got {got}, want {exp}"
            );
        }
    }

    #[test]
    fn array_weights_prwts_reml_matches_r() {
        let (e, design, wt) = gbg_fixture();

        // arrayWeights(E, ~group, weights = W, method = "reml").
        let w = array_weights_prwts_reml(&e, &design, &wt, None, 10.0, 50, 1e-5);
        let want = [
            1.5867284550700409,
            1.1019127664080206,
            1.2065279057943283,
            1.4157105291721905,
            0.29591187727091722,
            1.1315557212822311,
        ];
        assert_eq!(w.len(), want.len());
        for (got, exp) in w.iter().zip(want.iter()) {
            assert!((got - exp).abs() < 1e-6, "p=2: got {got}, want {exp}");
        }

        // Intercept-only design (p = 1), same E / W.
        let narrays = e.ncols();
        let design1 = Array2::<f64>::ones((narrays, 1));
        let w1 = array_weights_prwts_reml(&e, &design1, &wt, None, 10.0, 50, 1e-5);
        let want1 = [
            1.3749226879021179,
            1.4906361441733864,
            1.0601401145509048,
            1.0761314591200781,
            0.62056380371792619,
            0.68918376453280328,
        ];
        for (got, exp) in w1.iter().zip(want1.iter()) {
            assert!((got - exp).abs() < 1e-6, "p=1: got {got}, want {exp}");
        }
    }

    #[test]
    fn array_weights_quick_matches_r() {
        let y = array![
            [-0.59, 0.01, 0.79, 0.36],
            [0.03, -0.19, -0.23, 0.65],
            [-1.52, -0.77, 1.67, 1.81],
            [-1.36, -0.22, 0.50, 1.22],
            [1.18, -0.98, 0.16, 0.91],
        ];
        let design = array![[1.0, 0.0], [1.0, 0.0], [1.0, 1.0], [1.0, 1.0]];
        let fit = crate::fit::lmfit(
            &y,
            &design,
            (0..5).map(|i| i.to_string()).collect(),
            vec!["Int".into(), "grp".into()],
        )
        .unwrap();
        let w = array_weights_quick(&y, &fit);
        let want = [
            0.759166824278653,
            0.759166824278652,
            1.46462963844169,
            1.46462963844169,
        ];
        assert_eq!(w.len(), want.len());
        for (got, exp) in w.iter().zip(want.iter()) {
            assert!((got - exp).abs() < 1e-9, "got {got}, want {exp}");
        }
    }

    #[test]
    fn contr_sum_shape() {
        let c = contr_sum(4);
        assert_eq!(c.dim(), (4, 3));
        assert_eq!(c[[0, 0]], 1.0);
        assert_eq!(c[[1, 1]], 1.0);
        assert_eq!(c[[3, 0]], -1.0);
        assert_eq!(c[[3, 2]], -1.0);
        assert_eq!(c[[0, 1]], 0.0);
        // Columns sum to zero.
        for j in 0..3 {
            let s: f64 = (0..4).map(|i| c[[i, j]]).sum();
            assert!(s.abs() < 1e-15);
        }
    }
}