public FitDataIterator(ITuple tuple) {
    this.tuple = tuple;

    tuple.start();
    tuple.next();

    valCol = tuple.findColumn("value");
    errCol = tuple.findColumn("error");
    errMinusCol = tuple.findColumn("minusError");

    nVars = tuple.columns() - 3;
    vars = new double[nVars];
  }
 public boolean next() {
   return tuple.next();
 }