1. 608组样本，第一列数字是标号，第二列数字是出现损坏的时间，第三列表示数据有效性，为0有效

2. 损坏时间是对数正态分布的，需要拟合

3. 求均值80%置信区间

4. 成本为m，价格为s，保证盈利20%，选取保修期

5. 比较保修期和拟合数据的均值

6. 若保修期就是拟合损坏时间的均值，求出利润率

loadd.m：加载样本数据，并选取有效数据
period.m：加载成本、价格数据，计算利润和保修期的关系(1.608 groups of samples, the first number is the label, the second column number is the time to appear damage, the third list shows the validity of the data, which is 0 effective.
2. damage times are logarithmic normal distribution and need to be fitted
3. mean in 80% confidence interval
4. the cost is m, the price is s, the profit is 20%, the warranty period is selected.
5. compare the mean value of the warranty period and the fitting data
6. if the warranty period is to fit the mean damage time, the profit rate is calculated.

Loadd.m: load the sample data and select the valid data
Period.m: loading cost, price data, and calculating the relationship between profit and warranty period)