code: function extractVerticalComponent(accelerometerData, attitudeData) {
          var res=[];
          var rm;
          for (var i=0;i<accelerometerData.length;i++){
              rm=new Matrix(module.exports.composeRotation(attitudeData[i][0],attitudeData[i][1],0)); 
              res[i]=new Matrix([accelerometerData[i][0],accelerometerData[i][1],accelerometerData[i][2]]).dot(rm).data[0][2];
          }
          return res;
      }
docs: Rotate accelerometer signal using attitude data and extract vertical component.
  Useful for instance for implementing a pedometer
  
  @param {2D array} (linear) accelerometerData 2D array containing time series of acceleration values [[x1, y1, z1],[x2, y2, z2],...]
  @param {2D array} attitudeData 2D array containing time series of attitude values [[pitch1, roll1, yaw1]. [pitch2, roll2, yaw2],... ] (in Radians)
  @returns {1D array} of vertical acceleration values [z1, z2,...]