public PhasorMatrix subarray_as_Phasor_columnMatrix(int start, int end){
        if(end>=this.length)throw new IllegalArgumentException("end, " + end + ", is greater than the highest index, " + (this.length-1));
        Phasor[] pp = this.getArray_as_Phasor();
        Phasor[] retArray = new Phasor[end-start+1];
        for(int i=start; i<=end; i++)retArray[i-start] = pp[i];
        PhasorMatrix mat = PhasorMatrix.columnMatrix(retArray);
        return mat;
    }