/**
 *  The `Accumulator` class is a data type for computing the running
 *  mean, sample standard deviation, and sample variance of a stream of real
 *  numbers. It provides an example of a mutable data type and a streaming
 *  algorithm.
 *  <p>
 *  This implementation uses a one-pass algorithm that is less susceptible
 *  to floating-point roundoff error than the more straightforward
 *  implementation based on saving the sum of the squares of the numbers.
 *  This technique is due to
 *  <a href = "https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Online_algorithm">B. P. Welford</a>.
 *  Each operation takes constant time in the worst case.
 *  The amount of memory is constant - the data values are not stored.
 *  <p>
 *  For additional documentation,
 *  see <a href="https://algs4.cs.princeton.edu/12oop">Section 1.2</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */
export default class Accumulator {
    private n;
    private sum;
    private mu;
    /**
     * Adds the specified data value to the accumulator.
     * @param  x the data value
     */
    addDataValue(val: number): void;
    /**
     * Returns the mean of the data values.
     * @return the mean of the data values
     */
    mean(): number;
    /**
     * Returns the sample variance of the data values.
     * @return the sample variance of the data values
     */
    var(): number;
    /**
     * Returns the sample standard deviation of the data values.
     * @return the sample standard deviation of the data values
     */
    stddev(): number;
    /**
     * Returns the number of data values.
     * @return the number of data values
     */
    count(): number;
    toString(): string;
}