Question

Unable to correct errors from my MatLab Script and would like to see a script to compare mine to.

Write a MatLab script that simulates a virus spread.

This problem needs the following parts, some of which are nested loops, ie Part 3, 4 and 5 are nested in Part 2’s loop (for or while):

To build the program first to only deal with infection transmission within the town’s neighbors

1. An array which for every person in the town which saves the value that corresponds to infection. -1 if recovered, 0 if never sick, 1-14 if infected, when the value =15 it should change to -1 recovered. The array has as many elements (at least, see 2 below) as townspeople.

2. A loop which checks every day, all townspeople, and for any infected person and increments their infection value in the array from Part 1, from 1 to 2, 2 to 3, etc until they reach day 15, at which the value is set to -1 (recovered). I checked first if they were already infected, and incremented the infection value, then I ran the inner loop from “Part 3” looking for new infections, then at the very end of this Part 2 loop, I counted the number of infected townspeople, and saved the number of infected in an array “NumInfected(d)”, where d is the day.

3. Within the “Day” loop above, we need a loop that compares each townsperson to their neighbors, i=1:1000, neighbors to the left and then to the right, and infects them if the random number generator requires it.

The person E(i-1), lives to the left, and E(i+1) lives to the right. Each day, for all 1000 townspeople, check first to see if the ith person E(i) is never infected (value E(i)=0), then check their neighbors. If E(i-1) is infected, compute the probability of infection and if it is > 1 then the ith person becomes infected E(i)=1. Check If E(i) =0, and now check whether E(i+1) is infected, compute the probability again, and if the probability is>1 then again E(i)=1.

When i=1 only check the E(i+1) neighbor, and i=1000 only check the E(i-1) neighbor, as they only have 1 neighbor. See “Part” 4 for how to check the probability of infection.

4. To check the probability of infection of ith person given an infected adjacent neighbor, use floor(P*rand). Set P=1.05, for this, “rand” produces 0 to 1. The value (P*rand) will be >1 if the rand function returns anything greater than 0.95, which will happen 1/20 times. The function floor( ) finds the lowest integer of (P*rand), so floor(P*rand)=0 if rand returns <0.95. If floor(P*rand)>0 the ith person will be infected by the infected neighbor. Every time you call rand, it will return another random number, 0 to 1.

5. Now plot NumInfected(d) versus d the day.

If this works, you should get some neighbor to neighbor transmission which dies off relatively quickly. If you change P from 1.05 (1/20 odds of transmission per day during infection period) to P = 1.2, you should get more sustained infection numbers.

Now, you can add the classes, there are several ways to do this.

6. In my program, I added a column to E, so E has a column whose E(ith,1) value corresponds to the infection value, -1,0,1-14 and a column whose E(ith,2) value corresponds to the classroom the person is in, 0,1, 2 (if using the revised specification) or 0,1,2,3,4 (with the original specification). Example for townsperson number 20, E(20,1)=14 on the 14^th day of infection, E(20,2)=1 if the person is in class 1, but E(20,2)=2 if the person is in class 2.
7. You can distribute the students across the first 1-25 or 26-50, etc townspeople, or across the town’s first 500, second 500, it is your choice. You can take two classes and distribute them across the whole town, so that every 40^th townsperson is a student, write a for loop from x:1:25 and E(x*40,2)=1 for class 1, E((x*40-20),2) = 2 for class 2. It is up to you, how to distribute the students, but you must distribute them.
8. This could be called Part 2.5. Before checking for neighborhood transmission, count the number of students in Class 1, 2 who are infected. NumInfClass(1), NumInfClass(2), etc This will require either a loop for each class, which checks all students in the class, or it can be a loop through the town, that adds all of the infected who are also in Class 1, Class 2, etc.
9. This can be added to Part 3, or added before or after Part 3. For all never infected students in a class, the probability of infection is now (for class 1), floor(NumInfClass(1)*P*rand), if this is >1, the student is infected, so the student can be infected by neighbors, and by other students in their class, and their odds of being infected increase with each infected classmate.

Now plot NumInfected(d) versus d the day.

Answer 1

Code:

townspeople = randi([0 14],1,1000); %assigning random infection value to 100 people.

pr=0;
pl=0;
hold on;
for d=1:25
numberinfected=0;
for i=1:1000
if townspeople(i)>0
townspeople(i)=townspeople(i)+1;%changing infection sttus
numberinfected=numberinfected+1;%changing number of infected status
end
if townspeople(i)==15
townspeople(i)= -1;
numberinfected=numberinfected-1;
end
if townspeople(i)==0 && i~= 1 && i~=1000
if townspeople(i-1) >0
pl=floor(1.05*rand);
end
if townspeople(i+1) >0
pr=floor(1.05*rand);
end

%pr is probability of infection due to right neighbour.

%pl is probability of infection due to left neighbour.

if pr >= 1 || pl >= 1
townspeople(i)=1;
numberinfected=numberinfected+1;
pr=0;
pl=0;
end
elseif townspeople(i)==0 && i== 1
if townspeople(i+1) >0
pr=floor(1.05*rand);
end
if pr >= 1
townspeople(i)=1;
numberinfected=numberinfected+1;
pr=0;
end
elseif townspeople(i)==0 && i== 1000
if townspeople(i-1) >0
pl=floor(1.05*rand);
end
if pl >= 1
townspeople(i)=1;
numberinfected=numberinfected+1;
pl=0;
end
  
end
end
plot(d,numberinfected,'*');

%% Plot the number of infected people for every day(***hold must be on***)
end

Output:

Second Part

townspeople = randi([0 14],1,1000);%assigning random infection value to 100 people.

%assigning class status

for k=1:1000
class(k)=0;
end

for k=20:20:1000
class(k)=2;
end

for k=40:40:1000
class(k)=1;
end

infclass1=0;
infclass2=0;
pr=0;
pl=0;
hold on
for d=1:25
numberinfected=0;
for i=1:1000
if townspeople(i)>0
if class(i)==1
infclass1=infclass1+1;
elseif class(i)==2
infclass2=infclass2+1;
end
  
townspeople(i)=townspeople(i)+1;%changing infection sttus
numberinfected=numberinfected+1;%changing number of infected status
end
if townspeople(i)==15
townspeople(i)= -1;
numberinfected=numberinfected-1;
end
if townspeople(i)==0 && i~= 1 && i~=1000
if townspeople(i-1) >0
pl=floor(1.05*rand);
end
if townspeople(i+1) >0
pr=floor(1.05*rand);
end

%determing class status for infected townpersons(***different varible named class is used***)

%pr is probability of infection due to right neighbour.

%pl is probability of infection due to left neighbour.

%pclass is probability of infection due to Classmates.
if class(i)==1
pclass=floor(1.05*infclass1*rand);
elseif class(i)==2
pclass=floor(1.05*infclass2*rand);
else pclass=0;
end
if pr >= 1 || pl >= 1 || pclass >=1 %checking whether the probability is more than 1 or not
townspeople(i)=1;
numberinfected=numberinfected+1;
pr=0;
pl=0;
pclass=0;
end
elseif townspeople(i)==0 && i== 1
if townspeople(i+1) >0
pr=floor(1.05*rand);
end

if class(i)==1
pclass=floor(1.05*infclass1*rand);
elseif class(i)==2
pclass=floor(1.05*infclass2*rand);
else pclass=0;
end
if pr >= 1 || pclass >=1  %checking whether the probability is more than 1 or not
townspeople(i)=1;
numberinfected=numberinfected+1;
pr=0;
end
elseif townspeople(i)==0 && i== 1000
if townspeople(i-1) >0
pl=floor(1.05*rand);
end

if class(i)==1
pclass=floor(1.05*infclass1*rand);
elseif class(i)==2
pclass=floor(1.05*infclass2*rand);
else pclass=0;
end

if pl >= 1 || pclass>1
townspeople(i)=1;
numberinfected=numberinfected+1;
pl=0;
end
  
end

end
plot(d,numberinfected,'*');
xlabel('Day');
ylabel('Number of Infected persons');
end

Output: