public ComplexMatrix subarray_as_Complex_rowMatrix(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();
        Complex[] retArray = new Complex[end-start+1];
        for(int i=start; i<=end; i++)retArray[i-start] = cc[i];
        ComplexMatrix mat = ComplexMatrix.rowMatrix(retArray);
        return mat;
    }