code: protected DoubleMatrix1D gradFiStepX(DoubleMatrix1D stepX){
  		
  		DoubleMatrix1D ret = F1.make(getMieq());
  		for(int i=0; i<getDim(); i++){
  			ret.setQuick(         i, - stepX.getQuick(i));
  			ret.setQuick(getDim()+i,   stepX.getQuick(i));
  		}
  		
  		return ret;
  	}
docs: Computes the term Grad[fi].stepX