Pert diagram (engineering network diagram)

Reprint ：https://blog.csdn.net/qqxyy99/article/details/53190013

One 、 Definition

remarks ：
1. node （ event ）： Circle in Figure , Indicates the end of the inflow node task , And start to flow out the task of the node . Only when all tasks flowing into this node are finished , Node events occur , The outflow node task starts .
2. critical path ： The sequence of events and activities that take the longest time in the diagram .
3. The earliest moment ： Refers to the node （ event ） The earliest possible occurrence time of .
4. Latest time ： The task starting from this event must start before this time , Otherwise, the whole project cannot be completed on schedule .
5. Relaxation time ： Indicates the flexibility to complete the task without affecting the whole construction period .

Two 、

Maybe the above explanation can't fully understand and do the right thing , But the formulas and tips we summed up when doing soft test questions are enough to cope with the exam . as follows ：

This problem requires finding out the minimum time of the project , Critical path .

First, calculate the length of each path ：
        1.ABEGJ:3+15+2+7=27
        2.ACFGJ:6+4+3+7=20
        3.ACFHJ:6+4+20+10=40
        4.ADFGJ:10+8+3+7=28
        5.ADFHJ:10+8+20+10=48
        6.ADFIHJ:10+8+4+10=32
        7.ADFIJ:10+8+4+12=34
To sum up, the longest is 48, Therefore, the minimum time is 48

Seeking activity FG Relaxation time
First of all, we should clarify the calculation of the four concepts ：
    ① Earliest start time （ The sum of the longest input streams before the starting point of a certain section of the project ）,
    ② At the latest （ critical path - The distance from the starting point to the final end point of the whole project ）,
    ③ End at the earliest （ The sum of the longest input streams before the end point of a certain section of the project ）,
    ④ At the latest （ critical path - The distance from the end point to the final end point of the whole project ）
According to the above concept, we can get
    ①10+8=18
    ②48-3-7=38
    ③10+8+3=21
    ④48-7=41
Relaxation time = At the latest - The first time ②-①=38-18=20
Relaxation time = Latest technology - End at the earliest ④-③=41-21=20
Another simple method ： Use critical path - The longest path of the desired activity is 48-10-8-3-7=20 Find the relaxation time .