code: public void updateRangesFirst(Instance instance, int numAtt, double[][] ranges) {
      for (int j = 0; j < numAtt; j++) {
        if (!instance.isMissing(j)) {
          ranges[j][R_MIN] = instance.value(j);
          ranges[j][R_MAX] = instance.value(j);
          ranges[j][R_WIDTH] = 0.0;
        }
        else { // if value was missing
          ranges[j][R_MIN] = Double.POSITIVE_INFINITY;
          ranges[j][R_MAX] = -Double.POSITIVE_INFINITY;
          ranges[j][R_WIDTH] = Double.POSITIVE_INFINITY;
        }
      }
    }
docs: Used to initialize the ranges. For this the values of the first
  instance is used to save time.
  Sets low and high to the values of the first instance and
  width to zero.
  
  @param instance 	the new instance
  @param numAtt 	number of attributes in the model
  @param ranges 	low, high and width values for all attributes