如何在低于阈值时开始计数，并在时间序列中停止计数高于相同阈值?

Question

我模拟了一整年的风速数据，现在我想计算风速低于某一阈值的连续小时数。我得找出低于这个阈值的最大连续时间。因此，它应该在达到阈值时开始计数，并在值再次超过阈值时停止计数。这种情况在一年中会发生多次，所以，就像我提到的，我寻找的是最大连续小时数

Windspeed_hourly_mean = xlsread('Windspeed_hourly.xlsx','D3:D8762');
WHM=Windspeed_hourly_mean;
threshold = 3;
isBelow = (WHM < threshold); % gives us a vector of logical values
isBelow = [false, isBelow, false]; % make sure the vector starts and ends with false
transitions = diff(isBelow); % gives 1 where false->true and -1 where true->false 
starts = find(transitions==1); % indexes of where each period starts
ends = find(transitions==-1); % indexes of where each period ends
durations = ends - starts;
max(durations) % largest duration

Answer 1

如果你有一个每小时风速值windSpeed的1 xn向量，你的阈值是threshold，那么:

isBelow = (windSpeed < threshold); % gives us a vector of logical values
isBelow = [false, isBelow, false]; % make sure the vector starts and ends with false
transitions = diff(isBelow); % gives 1 where false->true and -1 where true->false 
starts = find(transitions==1); % indexes of where each period starts
ends = find(transitions==-1); % indexes of where each period ends
durations = ends - starts;
max(durations) % largest duration

需要将false添加到isBelow向量的开始和结束，以便在每个结束之前都有一个开始，并且使ends向量与starts向量长度相同。