Unsupervised PBMC scATAC Batch Integration

Single-cell data is collected in separate batches (samples, labs, runs), and technical batch effects can dominate and obscure real biology. You inherit a no-correction PCA embedding (which keeps batch variation) and must produce a low-dimensional embedding that removes batch variation while preserving cell-type structure, using only each cell's binary peak set and its batch label. The embedding is re-computed by a sealed verifier on a hidden split and scored by how well cell types stay clustered, so only a method that genuinely integrates across batches counts.

Hard Constraints

• Submit an algorithm (embed), not a precomputed embedding — the verifier re-runs your code on hidden cells.
• Keep the exact signature embed(atac, batch_labels, peak_names) -> np.ndarray (n_cells, d).
• Input peaks are binary; you also receive each cell's integer batch id. You do not receive cell-type labels — the embedding must be unsupervised w.r.t. cell type (the judge uses cell types only for scoring).
• Output a real-valued embedding with a modest d in [2, 512] (e.g. 10–128); finite values, one row per input cell, or the submission scores 0.
• There is no network at grade time. Do not hardcode or look up answers.

What You Have

• The workspace /app/:
• Visible data (/app/data/): pbmc_atlas_atac.h5ad — binary peak-cell matrix (var_names="chr-start-end") with obs['batch'] and (for local scoring only) obs['annot'].
• The editable baseline /app/methods/main/ — this directory is what gets graded: the no-correction PCA embedding. Improve it in place or rewrite it entirely.
• Your self-check surface (free): python /app/selfcheck.py runs your embedding on the visible cells and reports cell-type NMI (best-over-resolution Leiden, or a KMeans fallback). This is a proxy — the sealed split differs, so a good self-check is necessary, not sufficient.

What You Submit

Edit /app/methods/main/solver.py to expose:

def embed(atac, batch_labels, peak_names):
    # atac         : scipy.sparse CSR (n_cells, n_peaks), binary {0,1}
    # batch_labels : np.ndarray (n_cells,) integer batch ids
    # peak_names   : list[str] length n_peaks, "chr-start-end"
    # returns      : np.ndarray float (n_cells, d) cell embedding, d in [2, 512]

You may add helper modules next to solver.py. The runtime provides numpy / scipy / scikit-learn / torch (and anndata / scanpy for the self-check). There is no submit step and no per-attempt feedback — self-check for as long as your run window allows, then leave your best solver.py in place; it is graded once at the end on the hidden cells.

How It Is Judged

After your run, the verifier runs your embed on the hidden split (your code runs in an isolated subprocess that receives only the peaks + batch ids, never the cell types). It clusters the embedding with Leiden at a grid of resolutions and scores the best normalized mutual information (NMI) between the clustering and the hidden cell-type labels:

metric = max over resolutions of  NMI(Leiden(embedding, res), cell_types)

The metric is cell-type NMI (higher is better). A no-correction embedding keeps batch variation; strong methods mix batches while keeping cell types separable.