Chapter 4 More Networks : Critical Path Analysis

Question 1

What is CPA all about

Answer 1

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

Question 2

How to do precedence tsble

Answer 2

Left make rows of all activities

Right what they depend on

Fill it out

Question 3

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!

Answer 3

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

Question 4

How to draw an ACTIVITY NETWORK!

Remember activity on arc, so what do we label !
Arrows!

Answer 4

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

Question 5

How to best draw activity network

Answer 5

Try no cross cross curved edges but if need be do it

Straight lines and make them meet,

Question 6

As we add arrows, what kinds graoh is this

Answer 6

A DIRECTED GRAPH, and thus has source snd sink

Question 7

Whenever drawing activity networks what’s the most I portsnt thing to do first when looking at precedence tsble

Answer 7

ALWAYS do the ones that depend on ONE THING FIRST, as might be sticky situation after

Question 8

Dummy line?

What value does it hold?

Do we need tk label?

Answer 8

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

Question 9

If ever get stuck as drawing wrong,

Answer 9

Just remember to do the one thst depends on one first , rub out and do sgsin

Question 10

How can we show how activities may have different weights on them?

Answer 10

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

Question 11

Early / late time?

Answer 11

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

Question 12

How to find early times for all

Last box early and late time?

How to find late for all

Answer 12

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

Question 13

Why going forward do we pick the latest, and backwards the earliest?

Answer 13

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

Question 14

Just remember rfirwar backward pass d

Answer 14

Forward big back small so time in middle as less

Question 15

What should source snd sink look like?

Answer 15

Source = 00
Sink = same same

Question 16

In an activity network there will always be critical activity and paths

What is a CRITICAL ACTIVITY
HOW TO IDENTIFY CRITICAL ACTIVITY

Answer 16

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

Question 17

What is the critical path

What does this mean

Answer 17

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

Question 18

Can we have more than one critical path?

Answer 18

Yes , can have multiple , but there will always be atleast 1!

Question 19

Which activities can float, and what dies float even mean

Answer 19

Float is the WRIGGLE room an activity , different times that represent the total amount it can wriggle by

Critical activites have NO FLOAT

Question 20

3 types of floats

Answer 20

Total float

Independent float

Interfering float

Question 21

What is the total float and how to find out

Answer 21

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

Question 22

What is independent float and how to find out

Explain the formula behind this

Answer 22

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!

Question 23

What is interfering float and how to find out

Answer 23

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

Question 24

Floats summary

Answer 24

Total = outer - outer - durstion

Indecent = inner - inner - durstion

Interfering = total - independent

Question 25

What are the floats for CRITICAL ACTIVITIES

Answer 25

Always 0!

Because if total 0, then indolent must be 0 and so is interniert

Question 26

IF TWO ACTIVITIES BOTH COME FROM SAME PLACE AND THEN GO INTO A NODE WHAT TO DO

Important !,

Answer 26

Must make one a dummy to ensure unique numbering, make a node and continue with numbering rather than CURVING LINE

Question 27

What does floats mean in context, so if I have 10 independent float, what does this now mean

Answer 27

I can take 10 days longer without changing anything

Question 28

What can a delay in time do to activities if exceeds floats

How to determine what has changed

Answer 28

Can cause some tk be critical (redo) and others not to be

Lit do forward and backward again with new times and you’ll see!

Question 29

Damn when deciding which one to reduce by, what to consider

Important

Answer 29

You want the overall project to be a day quicker

Thus if it’s not critical then no point

And if it is critical have to consider if it GURANTEES a reduction in time, as I’d there are two critical paths, then have to chose the one thst sffected both so both are reduced by one day, and overall no matter what project is taken back

Must pick thing that affects ALL THE CRITICAL PATHS

Question 30

How to draw Gantt chart cascade diagram

Answer 30

Time in x axis

Critical activites on bottom row together, start snd end time

If another critical path add on row above , but don’t repeat

2) then for every activity not criticsl, own row
- start, finish, dotted line for late finish as float

Continue

NO VERTICAL AXIS, that’s for number of workers

Question 31

How to do restliche history’s, and manipulate to get lower workers net

Answer 31

Y AXIS THIS TIME WITH WORKERS!
1) from cascade diagram, drop the things like gravity
- critical row drips
- then other activtiesdrop

SCALE THEM WITH SLIDER TO GET LEAST AMOUNT OF WORKERS AS OOSSIBLE

Question 32

Difference with cascade and resource?

Answer 32

Resource has worked y axis too, with gravity drop

And you can move the activity based on their floats to get optimal least amount of workers working at ince

Question 33

What can resource diagram show , if they’re at early times or moved around

Answer 33

If just drop like gravity, will show amount of workers needed per day if activites start at specific times

However through manipulation, csn schedule kther activitues to start so thst won’t need ss m any eorkers

Question 34

How to find the LONGEST and shortest route in a netowkr

Answer 34

Longest = CPA on a network, and is the paths of CRITICAL ACTIVITY!, where the length is final length

shortest = dijkstram don’t forget to GIVE THE ROUTE TOO

Question 35

Two assumptions can be made when doing cpa?

IMPORTSNT

Answer 35

That activities take SXACTLY WHOLE NUMBER OF DAYS TO COMPLETE ( very unrealistic)

There is no turnover time between activities (also unrealistic )

Question 36

How to determine what an activity is INTERFERING WITH properly

Answer 36

Check activity behind and ahead, and look for an activity that is SOLELY dependent on activity you’re moving, because now if you move this it will definitely affect that one, whereas if the activity depends on soemthign else moving your activity might not have an affect, as the other one depends more on another!

So check for SOLE DEPENDENCE