相位转换为双比特，为什么最后一次判断不成功

Question

想把相位转化为对应的双比特

2*pi	1.5*pi	pi	0.5*pi
00	10	11	10

rel_code = zeros(1,10);
rel_phase = [2pi 1.5pi 2pi pi 1.5pi ];
for n=1:5
switch rel_phase(n)
case 1.5pi
rel_code(2n-1) = 1 ;
rel_code(2n) = 0;
case 2pi
rel_code(2n-1) = 0 ;
rel_code(2n) = 0;
case pi
rel_code(2n-1) = 1 ;
rel_code(2n) = 1;
case 0.5pi
rel_code(2n-1) = 0 ;
rel_code(2*n) = 1;
end
end

结果

​ rel_code =

​ 1 至 7 列

​ 0 0 1 0 0 0 1

​ 8 至 10 列

​ 1 0 0

rel_code(9:10)应该是10才对，不知道为什么，最后一次判断时没有反应