public double[] subarray_as_imaginay_part_of_Complex(int start, int end){
        if(end>=this.length)throw new IllegalArgumentException("end, " + end + ", is greater than the highest index, " + (this.length-1));
        Complex[] cc = this.getArray_as_Complex();
        double[] imag = new double[end-start+1];
        for(int i=start; i<=end; i++)imag[i-start] = cc[i].getImag();
        return imag;
    }