Chapter 4 More Networks : Critical Path Analysis Flashcards
What is CPA all about
This is using networks to build a project overview , so showing what tasks depends on what , and then seeing how best and how can we SCHEDULE THESE as they will take certain times, seeing if we have to time to spare / not
Then also representing on a gantt chsrt to see if we can get less workers if we start things on different days if we are allowed to
How to do precedence tsble
Left make rows of all activities
Right what they depend on
Fill it out
If last task in lrecedence table says can only be done once all activities are done, what should you try and do?
Quick way to do this!
Yiu should try and SIMPLIFY if you can
So if c depends on A, putting c down means you put A, don’t need so cross out !
2) just look at all activities that haven’t been mentioned before so add those in as these are the only ones that it will depend on
How to draw an ACTIVITY NETWORK!
Remember activity on arc, so what do we label !
Arrows!
Starter node label each node , so start with 0
Then arrows anything coming out that dint depend on anything first, label the ARROWS , not nodes
3) then any time something DEPENDS on something, we put a node down!
- remember to LABEL
4) finally add an end node and label
MAKE SURE TO ADD ARROWS
How to best draw activity network
Try no cross cross curved edges but if need be do it
Straight lines and make them meet,
As we add arrows, what kinds graoh is this
A DIRECTED GRAPH, and thus has source snd sink
Whenever drawing activity networks what’s the most I portsnt thing to do first when looking at precedence tsble
ALWAYS do the ones that depend on ONE THING FIRST, as might be sticky situation after
Dummy line?
What value does it hold?
Do we need tk label?
This allows you to connect things so that precedence is maintained snd still works
Holds a value of 0
No label, just arrow, an extension of one thing
If ever get stuck as drawing wrong,
Just remember to do the one thst depends on one first , rub out and do sgsin
How can we show how activities may have different weights on them?
After drawn activity network, now these activities could have WEIGHTS ON THEM
This could mean they have certain times taken to do it, cost etc
We can do analysis on them tk see what leeway there js
Early / late time?
Box on every node
Early shows earliest can start, or activity before can finish
Late shows latest activity before can finish or activity can starts
If activity before is past late time , or activity ahead starts later, WHOLE PROJECT IS LATE
How to find early times for all
Last box early and late time?
How to find late for all
FORWARD PASS
= consider all paths going into node (must KNKW ALL THE PATHS GOING IN)
- add the weights to current earliest
AND PICK THE LARGEST CHOICE !!!
The last box EARLY AND LATE TIME THE SAME
2) backwards pass, need to know all the arcs going back,
Subtrsvt the weights from current late
and pick the EARLIEST TIME
Why going forward do we pick the latest, and backwards the earliest?
Going forward, if you like an early one, then one of activities it has depended on HASNT HAPPEND YET, must pick the latest
Going backwards have to too or will overrun
Just remember rfirwar backward pass d
Forward big back small so time in middle as less
What should source snd sink look like?
Source = 00
Sink = same same
In an activity network there will always be critical activity and paths
What is a CRITICAL ACTIVITY
HOW TO IDENTIFY CRITICAL ACTIVITY
This is an activity that MUST start on time or whole project will overrun
Can identify as has same start start end end for two nodes, and the distance in between= the distance needed to go from 1st node to second
What is the critical path
What does this mean
Path cknnected by numerous critical activities from START TO END NODE
A list of activities thst must be completed on time or whole project overrun
Can we have more than one critical path?
Yes , can have multiple , but there will always be atleast 1!
Which activities can float, and what dies float even mean
Float is the WRIGGLE room an activity , different times that represent the total amount it can wriggle by
Critical activites have NO FLOAT
3 types of floats
Total float
Independent float
Interfering float
What is the total float and how to find out
This it the TOTAL amount the activity can move left or right essentially like a slider , the total amount it can wriggle
So OUTER - OUTER - activity duration
(Late finish - early start), have to - duration as on slider tbis takes some distance , want total distance remaining
What is independent float and how to find out
Explain the formula behind this
This is total float it can do WITHOUT forcing previous activity to finish at specific time or next to start at specfic
= INNER - INNER - DURSTION
If it’s negative = 0!
2) if you consider the outer, then starting at this time will mean activity before must finish early to hit this, so interfere, and right outer finishing at this time means activity before CANT START at the early start time
The fire, you must consider thr INNERS only, as these don’t limit how much the activity before or after csn start by
Remember duration!
What is interfering float and how to find out
Float available that will defo eat in to previous and force next to start at specfic time
= TOTAL - float that diesn’t cause any problem
= TOTAL - INDEPENDENT
Floats summary
Total = outer - outer - durstion
Indecent = inner - inner - durstion
Interfering = total - independent
