code: function evaluateLinear (pointsToEvaluate, functionValuesX, functionValuesY) {
    var results = []
    pointsToEvaluate = help.makeItArrayIfItsNot(pointsToEvaluate)
    pointsToEvaluate.forEach(function (point) {
      var index = help.findIntervalLeftBorderIndex(point, functionValuesX)
      if (index == functionValuesX.length - 1)
        index--
      results.push(linearInterpolation(point, functionValuesX[index], functionValuesY[index]
        , functionValuesX[index + 1], functionValuesY[index + 1]))
    })
    return results
  }
docs: Evaluates interpolating line/lines at the set of numbers
  or at a single number for the function y=f(x)
  
  @param {Number|Array} pointsToEvaluate     number or set of numbers
  for which polynomial is calculated
  @param {Array} functionValuesX             set of distinct x values
  @param {Array} functionValuesY             set of distinct y=f(x) values
  @returns {Array}