import type { PpkInput, PpkResult } from './types.js';
/**
 * Calculate Process Performance Index (Ppk)
 * Similar to Cpk but uses overall (long-term) standard deviation
 *
 * Pp = (USL - LSL) / 6sigma  (process spread)
 * Ppu = (USL - mu) / 3sigma   (upper capability)
 * Ppl = (mu - LSL) / 3sigma   (lower capability)
 * Ppk = min(Ppu, Ppl)    (process performance)
 *
 * @remarks
 *   Field naming is aligned with `cpk()` for a symmetric capability/performance API:
 *   prefer `ppu`/`ppl`/`sigmaLevel`. The legacy `ppUpper`/`ppLower`/`sigma` fields are
 *   retained as deprecated aliases (identical values) and will be removed in a future release.
 *
 * @param input - Ppk input parameters
 * @returns Ppk analysis result
 */
export declare function ppk(input: PpkInput): PpkResult;
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