Презентация на тему Lab Fall 2016

are the objectives?
Minimize aircraft losses
Minimize the number of days

to kill the target set
Meet investment limit (which is subject to discussion)
We will have to decide how to trade between these three objectives, so we have a goal program
What are the variables?
The number of weapons to buy
The assignment of weapons to targets in each scenario
The assignment of sorties (one aircraft flying to one target) in each scenario
We might need other variables too

parameters will have to be varied?
Overall investment: opinion ranges

from $35M - $200M
Probabilities of the 3 scenarios
Fortunately, people seem to agree on everything else
However, the fact that certain things have to be varied may affect the design of the model

model?
Multiple scenarios => two-stage recourse model
Multiple goals => some

sort of goal program
Final model will have to combine goals with two-stage recourse formulation
However, we need to work on some things with the basic 1-scenario problem
How do we determine the length of the bombing campaign?
How do we enforce all the conditions on using certain bombs in certain weather conditions?
What variables will we need to represent all this?

probably the hardest part of this project
Take the SSC

scenario
It has bad weather 30% of the time (proportion 0.3)
We can fly 90 sorties per day in this scenario
If we need to fly 270 sorties in bad weather, it will take 270 / (90*0.3) = 10 days on average to do it
But why fly in bad weather at all?
We still want to minimize the time to conduct the campaign
Not flying in bad weather increases campaign length by at least 30% (and gives the enemy an unearned advantage)

question the students raised in this project
There are 6

target types ( 3 collateral damage X 2 hardness)
Does each target type have to be killed in proportion to the weather?
Example: SCC has 120 soft targets with strict collateral damage requirements. Do we have to kill 40% in good weather (48), 30% in fair weather (36), and 30% (36) in bad weather?
Answer
No, these are fixed targets (e.g., buildings)
We can attack them whenever we want
We do NOT need to constrain the number attacked to weather proportions
However, we still need to track the TOTAL number of sorties flown in various weather conditions
An aside
You could argue that you need to constrain attacks to weather, because the enemy might use certain buildings on certain days

the sub-model
days required for scenario >= total sorties flown

in weather condition / (sorties per day in scenario X proportion of time in weather condition)
We need this constraint for every weather condition
So, days required will be the maximum
Another question: can sorties assigned be fractional?
Answer: yes, we are working with expected values for kills and attrition
Example: A GPS PK = 0.6 => 1/0.6 = 1.67 bombs on average required for kill
2 GPS bombs per sortie / 1.67 bombs required => 1.2 sorties required on average to kill the target
Since those numbers are fractional, it is OK to use fractional (continuous) sortie assignments
We are treating the sortie assignments as expected values

weather states
LGB (laser-guided bomb) requires good weather
GPS bomb works

in all weather states, but is less accurate and requires more on average to get a kill
Certain bombs have unacceptable collateral damage
Enormous consideration in modern warfare
Unguided weapons can have large miss distances due to wind and often hit unintended targets
However, guided weapons are much, much more expensive
So, the assignment variables ...
Must be a function of scenario, target type (hardness and collateral damage), and weather

MPL code
As usual, the first step is to write

the indexes

INDEX

e := (MTW1,MTW2,SSC) {theater}
b := (soad,gps,lgb,unguided) { weapon type }
c := (strict, medium, none ) {collateral damage category }
h := (hard, soft ) { target hardness }
w := (good, fair, bad ) { weather state }

sets to define allowable combinations of things
Here are the

sets I defined, in MPL:

{ allowable weapon and weather combinations }

wxw[b,w] := (soad.good, soad.fair, soad.bad,
gps.good,gps.fair,gps.bad,lgb.good,
unguided.good, unguided.fair );

{ allowable weapon and collateral damage combinations }

cda[b,c] := (lgb.strict, lgb.medium, lgb.none,
soad.medium, soad.none,
gps.medium, gps.none,
unguided.none )

of the aims of the project was to teach

students how to get higher-dimensional data into MPL
See the MPL code for all of it; but here are examples

{ target data by scenario, collateral damage, hardness }

TGTS[e,c,h] := [MTW1,strict,hard,200,
MTW1,strict,soft,400,
MTW1,medium,hard,400,

PK[b,e,h] := [soad,MTW1,soft,.86,
soad,MTW1,hard,.60,
soad,MTW2,soft,.77,

ATR[e,b,w] := [ MTW1, soad, good, .0001,
MTW1, soad, fair, .0001,
MTW1, soad, bad, .0001,
MTW1, lgb, good, .005,
MTW1, lgb, fair, .007,

Initial decisions: this is the number of bombs bought
Everything

else: these are decisions made in each scenario (indexed by e)
Here are the variables I used
Note the use of the multidimensional sets to limit allocation variables to allowed combinations
This is a good way to use the MPL “IN” operator

VARIABLES

bought[b]; { Weapons bought }

attr[e]; { Attrition by theater }

days[e]; { Days to prosecute campaign by theater }

{ Sorties allocated by scenario, weapon, target damage/hardness, and weather }

sorties[e,b,c in cda, h, w in wxw];

the project
And, there are several choices of how to

do it
There are 3 factors
Total aircraft attrition (losses)
Expected days to complete the campaign
Money spent on weapons
I used a weighted objective, but:
I knew I would make several runs
I could get a “near-preemptive” goal program by using large and small weights
I could control the budget by a simple constraint, and easily test many budgets

at here?
Wanted mostly to minimize expected days (weight =

1)
Gave a small weight to attrition to make sure that it was considered (break ties among near-identical solutions)
I did not weight the cost; I handled that via a budget constraint
Note the use of the MPL MACRO function

DAYWGT := 1;
ATTRWGT := 0.0001;
COSTWGT := 0;

MACRO

bcost:=sum(b: COST[b]*bought[b]);

MODEL

Min weighted = DAYWGT*SUM(e: PROB[e]*days[e]) +
ATTRWGT*SUM(e: PROB[e]*attr[e]) +
COSTWGT*bcost;

bcost < BUDGET;

{ Kill constraints }

SUM(b,w: PK[b,e,h]*LOAD[b]*sorties[e,b,c,h,w]) > TGTS[e,c,h];

buys[e,b]: { Buy and inventory constraints - by scenario }

SUM(c,h,w: LOAD[b]*sorties[e,b,c,h,w]) < INV[b] + bought[b];

expattr[e]: { Expected attrition by scenario - passenger constraints }

attr[e] = SUM(b,c,h,w: ATR[e,b,w]*sorties[e,b,c,h,w]);

daysreq[e,w]: { Days required by scenario - passenger constraints }

SRTD[e]*WX[e,w]*days[e] > SUM(b,c,h: sorties[e,b,c,h,w]);

bcost < BUDGET; { Total spent on weapons }

BOUNDS

bought[b] < MAXBUY[b];

computed as a convenience to make the model easier

to understand
Could be substituted out
The “passenger constraints” are there to compute the passenger variables attr[e] and days[e]
You might be tempted to use the MPL MACRO function, but MPL does not allow macros to be indexed
Note also the daysreq constraints
The constants are multiplied on the LHS, rather than divided on the RHS
Again, MPL doesn’t like dividing constants in equations

description, the model is:
Fairly simple
Combines a goal program and

a recourse model
Allows easy adjustments to the three goals to see how the answers change
But what was hard?
Figuring out how to do weather and days required for the campaign
Getting the data into MPL
Getting MPL to limit weapon-target-weather assignments to allowed combinations
Coming up with a goal structure to allow different runs

shows the cases I ran initially
17 combinations of budget,

scenario probabilities, and weights on attrition and days
This was more of an “exploratory analysis” to see broad trends
Large variations in answers
10 – 22 days for campaign, 16 – 24 aircraft lost for MTW-2
GPS bomb buys range from 0 – 2788
But some things don’t change ...
We never buy any new unguided weapons
Little variation in MTW-1 days for campaign, SSC attrition
Overarching conclusion: how much do you want to spend to improve MTW-2 outcomes?