MIME-Version: 1.0 Content-Location: file:///C:/50791E94/Bus132bTipsforStudyingPERT.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" Tips for the Study of PERT

Tips for the Study of PERT

 

I hope that the following suggestions will be helpful = in your study of the PERT topic.  This list is of course not exhaustive one.  In particular, for the stat portion see the special file on my home page.

 

1)  Solve= one complex problem completely before turning to the next one.  It is a mistake to do one problem = 80 percent and then turn to the next and solve it too 80 percent.  PERT problems are essentially conceptually similar to each other.  Thus mastering one completely will = sharply increase your chance to solve any other.

 

2) The challenge in solving PERT problems is in the internalizing  o= f the great number of details in the conceptual formal (notational and definitional) and computation development.

 

3). To help mastering the complexity, we break the PERT treatment to the following topics and within a topic to some subtopics.   The topics are:

A) Set Up

B) Event Scheduling

C) Activity Scheduling

D) Statistics.

 

So make sure to simply check if you have the full understanding of each topic.

 

Set Up

4)  In a = set up, notice the following:

      a. There i= s no loose activity.  Every activit= y is an arrow that must start at an event and end in         an event.

       b. O= nly the dummy activity arrow is marked as a dashed arrow.

 

5). In a Set Up, remember that the greatest challenge = is that of dealing with dummy variables.

     

Dummy Activities.  The need for those arise only when= some activity, x, requires only a subset of activities required by some other activity, y.   The activities in this subset are obviously commonly required by both x and y.

 

These common activity (ies= ) in the subset would be set up first, leading to some event (I)=  whose declaration allows the logical start of x.

 

The uncommon activities in the set are leading to even= t (II) whose declaration would allow y to begin.

 Since st= arting Y requires also the inputs of the common inputs, a dummy directed from (I) to (II) will be drawn.  Declarati= on of event (II) would mean that all inputs have been completed and activity y can begin.

 

6) Please notice, the complexity can be by far larger,= for example x requires as inputs a subset of activities that y requires as inpu= ts, while the inputs for y are only a subset of inputs required by z, etc.   While the principle of const= ructing the dummies is as described in 5), it is important to practice with differe= nt more complex cases, so it worthwhile to invent some complex cases and deal with them constructing the proper dummy activities.

 

Event Sche= duling

 

7) Remember the notations a square for TE a circle for= TL a triangle for event slack. TL-TE.

 

8) Use different colors:  Blue for TE, = RED for TL, Black for event slack.  When = you process red you need not pay attention to the numbers in blue and this will reduce considerably the chance for computational mistake.

 

9) Please remember:&n= bsp; Earlier time is smaller that later time. And there is no negative ti= me.

 

10)  Unde= rstand conceptually the logic in setting up both TE (LEFT) and TL (ELST).

Pay particular attention to TL.  Most students face no difficulty i= n computing TE.  The difficulty is in TL.  

 

TE’s computation dea= ls with the event as a summary point and considers only the activities leading to t= he event. 

TE assumes that all activities leading to the event can be completed by TE.

 

TL deals with the event as initiation point and consid= ers the activities that are starting from the event.

TL assumes that all activities starting from the event can start by TL without delaying the proje= ct.

Activity Scheduling 

 

11) Do not mix up the notation for start and finish of activities ( ES, LS, EF, LF ) with the notations for earliest and latest declaration of events (TE, TL). 

 

12) Process the table of activity scheduling by column= .  It is much easier.

 

Consider any activity x starting at event (I) and targeted to event (II).

 

ES, the earliest starting time for x is simply, TE for event (I), which is the number marked inside the square by event (I).   

Similarly, LF, the latest finishing time for x is simply, TL for event (II), wh= ich is the number marked inside the circle by event (II).

 

Compute the EF columns by adding (t), the activity time column and the ES column

Compute the LS column by subtracting (t) from the LF c= olumn.

 

13) The activity slack is the gap between the LS and ES column or alternatively equivalently the gap between the LF and LS columns.  This can be used to = check for possible mistakes in the columns computation.

 

14) Again, latest time is always greater than earliest= time and there is no negative time.