export type BM25Method = "robertson" | "lucene" | "atire";
export interface BM25Options {
    k1?: number;
    b?: number;
    method?: BM25Method;
}
export interface RetrieveResult {
    documents: number[][];
    scores: number[][];
}
export declare class BM25 {
    readonly k1: number;
    readonly b: number;
    readonly method: BM25Method;
    private _numDocs;
    private _avgdl;
    private _docLengths;
    private _invertedIndex;
    private _idf;
    private _indexed;
    constructor(options?: BM25Options);
    get numDocs(): number;
    index(corpusTokens: string[][]): void;
    private _computeIDF;
    getScores(queryTokens: string[]): number[];
    retrieve(queryTokensBatch: string[][], k: number): RetrieveResult;
    private _ensureIndexed;
}
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