function _mad(array) {
    array = flatten(array.valueOf());

    if (array.length === 0) {
      throw new Error('Cannot calculate median absolute deviation (mad) of an empty array');
    }

    try {
      var med = median(array);
      return median(map(array, function (value) {
        return abs(subtract(value, med));
      }));
    } catch (err) {
      if (err instanceof TypeError && err.message.indexOf('median') !== -1) {
        throw new TypeError(err.message.replace('median', 'mad'));
      } else {
        throw improveErrorMessage(err, 'mad');
      }
    }
  }
Compute the median absolute deviation of a matrix or a list with values.
The median absolute deviation is defined as the median of the absolute
deviations from the median.

Syntax:

    math.mad(a, b, c, ...)
    math.mad(A)

Examples:

    math.mad(10, 20, 30)             // returns 10
    math.mad([1, 2, 3])              // returns 1
    math.mad([[1, 2, 3], [4, 5, 6]]) // returns 1.5

See also:

    median, mean, std, abs

@param {Array | Matrix} array
                       A single matrix or multiple scalar values.
@return {*} The median absolute deviation.