# LowPass
# 函数简介
本函数对输入序列进行低通滤波，提取低于截止频率的分量。输入序列的时间戳将被忽略，所有数据点都将被视作等距的。
函数名： LOWPASS
输入序列： 仅支持单个输入序列，类型为 INT32 / INT64 / FLOAT / DOUBLE
参数：
wpass：归一化后的截止频率，取值为(0,1)，不可缺省。
输出序列： 输出单个序列，类型为DOUBLE，它是滤波后的序列，长度与时间戳均与输入一致。
提示： 输入序列中的NaN将被忽略。
# 使用示例
输入序列：
+-----------------------------+---------------+
| Time|root.test.d1.s1|
+-----------------------------+---------------+
|1970-01-01T08:00:00.000+08:00| 2.902113|
|1970-01-01T08:00:01.000+08:00| 1.1755705|
|1970-01-01T08:00:02.000+08:00| -2.1755705|
|1970-01-01T08:00:03.000+08:00| -1.9021131|
|1970-01-01T08:00:04.000+08:00| 1.0|
|1970-01-01T08:00:05.000+08:00| 1.9021131|
|1970-01-01T08:00:06.000+08:00| 0.1755705|
|1970-01-01T08:00:07.000+08:00| -1.1755705|
|1970-01-01T08:00:08.000+08:00| -0.902113|
|1970-01-01T08:00:09.000+08:00| 0.0|
|1970-01-01T08:00:10.000+08:00| 0.902113|
|1970-01-01T08:00:11.000+08:00| 1.1755705|
|1970-01-01T08:00:12.000+08:00| -0.1755705|
|1970-01-01T08:00:13.000+08:00| -1.9021131|
|1970-01-01T08:00:14.000+08:00| -1.0|
|1970-01-01T08:00:15.000+08:00| 1.9021131|
|1970-01-01T08:00:16.000+08:00| 2.1755705|
|1970-01-01T08:00:17.000+08:00| -1.1755705|
|1970-01-01T08:00:18.000+08:00| -2.902113|
|1970-01-01T08:00:19.000+08:00| 0.0|
+-----------------------------+---------------+
用于查询的SQL语句：
select lowpass(s1,'wpass'='0.45') from root.test.d1
输出序列：
+-----------------------------+----------------------------------------+
| Time|lowpass(root.test.d1.s1, "wpass"="0.45")|
+-----------------------------+----------------------------------------+
|1970-01-01T08:00:00.000+08:00| 1.9021130073323922|
|1970-01-01T08:00:01.000+08:00| 1.1755704705132448|
|1970-01-01T08:00:02.000+08:00| -1.1755705286582614|
|1970-01-01T08:00:03.000+08:00| -1.9021130389094498|
|1970-01-01T08:00:04.000+08:00| 7.450580419288145E-9|
|1970-01-01T08:00:05.000+08:00| 1.902113046743454|
|1970-01-01T08:00:06.000+08:00| 1.1755705212076808|
|1970-01-01T08:00:07.000+08:00| -1.1755704886020932|
|1970-01-01T08:00:08.000+08:00| -1.9021130222335536|
|1970-01-01T08:00:09.000+08:00| 3.552713678800501E-16|
|1970-01-01T08:00:10.000+08:00| 1.9021130222335536|
|1970-01-01T08:00:11.000+08:00| 1.1755704886020932|
|1970-01-01T08:00:12.000+08:00| -1.1755705212076801|
|1970-01-01T08:00:13.000+08:00| -1.902113046743454|
|1970-01-01T08:00:14.000+08:00| -7.45058112983088E-9|
|1970-01-01T08:00:15.000+08:00| 1.9021130389094498|
|1970-01-01T08:00:16.000+08:00| 1.1755705286582616|
|1970-01-01T08:00:17.000+08:00| -1.1755704705132448|
|1970-01-01T08:00:18.000+08:00| -1.9021130073323924|
|1970-01-01T08:00:19.000+08:00| -2.664535259100376E-16|
+-----------------------------+----------------------------------------+
注：输入序列服从