Function cosh

src/compute-engine/interval/trigonometric.ts:352–367

(x: Interval | IntervalResult)

}

/**
 * Hyperbolic cosine.
 *
 * Domain: all reals, minimum at x=0.
 */
export function cosh(x: Interval | IntervalResult): IntervalResult {
  const unwrapped = unwrapOrPropagate(x);
  if (!Array.isArray(unwrapped)) return unwrapped;
  const [xVal] = unwrapped;
  if (xVal.lo >= 0) {
    return ok({ lo: Math.cosh(xVal.lo), hi: Math.cosh(xVal.hi) });
  } else if (xVal.hi <= 0) {
    return ok({ lo: Math.cosh(xVal.hi), hi: Math.cosh(xVal.lo) });
  } else {
    // Contains zero - minimum is cosh(0) = 1
    return ok({
      lo: 1,
      hi: Math.max(Math.cosh(xVal.lo), Math.cosh(xVal.hi)),
    });