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Critial path : total float & longest path option

16 replies [Last post]
Wed, 2007-08-01 06:58
Khuong Do
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Hi All

There are 2 option to determine Critical path in Primavera : Total float <=0 and longest path
I wonder when we should use longest path instead of Total float <=0 .
Could you give some reality example of situation that we should use longest path?

Thanks & regard
Khuong
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Replies

Sun, 2007-08-05 00:56
#1
Andrew Dick
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Khuong,
I’m interested in your thoughts on the multiple calendar idea and the resultant float, as I’m relativley new to Primavera (Going on 7 months now) I have been interested as to how the float is calculated, mostly because I get some weird answers that don’t make sense.

As I deal with hard mandatory constraints on a daily basis given the nature of our work and the unfortunate circumstance of the customer issuing the contracts way too late, and the now added complexity of using resource leveling, any converstation on this topic or the like is of great interest to me at this time.

Apart from Ron and Paul’s sites, does anyone else have any other information they could pass onto me?

andrewtdick@optusnet.com.au
Thanks
Andy

P.S. Paul Harris has just recently published a paper I wrote on resource leveling, and I can say that I’m seeing many benefits in my schedules as a result of this method, I’m currently working on a range of processes, including code structures and resource assignment protocals to further enhance these ideas of mine.
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Sun, 2007-08-05 00:38
#2
ulysses garcia
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In my own thinking, a contract which imposes a milestone with mandatory constraint is considered bad contract....more worst thing if it falls along the critical path..
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Sat, 2007-08-04 16:43
#3
KIAN GHADAKSAZ
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Hi All
My point of view,Suppose according to contract you should define some milestones which should be fixed by constraint on the schedule(contract obligations),during execution phase,all activities which havn’t met mentioned milestones and passed,have total float=0 or less than 0,but are not necessarily on the longest path,therefore we have some activities on the longest path that could have float and some other activities which have 0 or negative total float without being on the longest path.

kian
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Thu, 2007-08-02 00:56
#4
ulysses garcia
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Enterprise will defer P3 in calendar algorithm, P3 uses calendar in predeccesor while P5,P6 use either succ or pred cal.
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Wed, 2007-08-01 22:30
#5
Khuong Do
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Hi Ravi

Yes you’re right. If project has 1 calendar assigned, longest path will be the same with TF=0.
Except WBS summary activity, most of WBS activity have TF=0 but didn’t not belong to longest path cause its Free float > 0.

Thanks
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Wed, 2007-08-01 09:20
#6
Oliver Melling
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The presentation you mentioned only covers P3.

Does P5 discount hammocks and give a true longest path?

Oliver
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Wed, 2007-08-01 08:47
#7
A D
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Thanks Dieter for the paper. Thats Beautifully written.

Dont know, how everytime, we end up with a PAUL HARRIS paper to come to a conclusion.

Cheers,

Raviraj
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Wed, 2007-08-01 08:36
#8
A D
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And Khuong,

One more thing.....

If there is only one calender assigned for the project, then LONGEST PATH is equal to TF=0

Am i correct?
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Wed, 2007-08-01 08:36
#9
Dieter Wambach
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Hi Raviraj
Thanks to Khuong there is the answer.
There is another good presentation from our collegue Ron Winter which may help:
www.primavera.com/partners/files/Longest_Path.pdf

A GPS navigation system all short pieces of way wouldnt be a great help for you, but the shortest way - just inverse algorithm.

Regards
Dieter
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Wed, 2007-08-01 08:34
#10
A D
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Hi Khuong,

Just one more query. Logic is correct because LONGEST path is derived from activities having early finish equal to latest calculated early finish for the project, but....

is it because of the different calender assignments used.

But, then what u r using - LONGEST PATH or activities having TF=0.

For me, it shud be LONGEST PATH.

Any suggestion guys???
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Wed, 2007-08-01 08:02
#11
Khuong Do
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Hi Raviraj

I’m afraid your statement is not right.

I’ll present 2 way of defining critical part.

1) Total Float less than or equal to ...
If using the Total Float option, Total Float is calculated as:

Finish Float = Late Finish - Early Finish
Start Float = Late Start - Early Start
Smallest float of start or finish

2) Longest path

The longest path activities are calculated by reviewing the
schedule backwards through the driving relationships AND
if the PREDECESSOR/SUCCESSOR combination has a
driving relationship between them then both activities are
flagged as part of the longest path. However, if the Free
Float (FF) of the predecessor is greater than 0, then the
longest path will end with that successor. This would
translate into the longest path not always going to the
beginning of the project.
Notes:
 All relationships are evaluated individually.
 The driving relationship flag is calculated based on
the relationship free float and the business rules for
driving relationships.
 Completed Activities are not added to the Longest
Path
 Longest Path is calculated using Successor Calendar
not Predecessor Calendar to calculate FF.

Thanks
Khuong
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Wed, 2007-08-01 07:45
#12
A D
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Yup Dieter,

I think its possible. C, its like this

All activities on LONGEST PATH will have TF = 0,
but activities having TF = 0, maynot be on the CRITICAL PATH

Does this sense correctly???

Cheers,

Raviraj
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Wed, 2007-08-01 07:40
#13
Dieter Wambach
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Hi Raviraj

in some cases, it is the same. In bigger projects it’s different but with some overlap.

Dieter
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Wed, 2007-08-01 07:34
#14
A D
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Hi Khuong,

Does, P3/P5 give any different critical path, in the above scenario (between TF=0 and for the LONGEST PATH)

Never tried...

Cheers,
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Wed, 2007-08-01 07:28
#15
Dieter Wambach
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Hi Khuong
I like this option. If a project plan, where many part project leaders are involved, has to be optimized because customer’s wish or the contract are not equal to the results of planning, it is more efficient. With the longest path there is a unique way through all subprojects. To optimize this path is much easier to understand than an activity here and an activity there.
Also, if managers ask for the critical path, its rather the longest path.
It’s just my experience.

Regards

Dieter
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Wed, 2007-08-01 09:45
#16
Dieter Wambach
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Oliver
It works with Level of Effort activities. For the rest, as far as I know, the algorithm of P3e/P5 is equivalent to P3.

Dieter
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