Vectors -Must- be the same length

So the problem here is line 38, where it would say

"Error using plot

Vectors must be the same length.

Error in x (line 37)

plot(t,I)"

And I know if it is in line 37, then it would likely be in line 47 as well. But I cannot see what is proccing the error message.

% Equations : dS/dt = -r S I
%             dR/dt = a I
%             dI/dt = -dS/dt - dR/dt - b I
% time measured in days
%S=susceptibles , R=recovereds, I=infecteds.
%             L=(S+R+I)(0)- (S+I+R)(t)
dt= 1.3 %time change
%r=1e-7
r=5e-8
a=0.05
%b=a*0.01
b=a*0.04
S0=8419000.
R0=0
I0=100
tmax=120 %number of days
popscale=8419000 %population scale for graphing
t=0:dt:tmax ;
S(1)=S0;
R(1)=R0;
I(1)=I0;
itmax=ceil(tmax/dt)
for it=2:itmax+1
    dSodt(it)=-r*S(it-1)*I(it-1);
    S(it)=S(it-1)+dSodt(it)*dt;
    dRodt(it)=a*I(it-1);
    R(it)=R(it-1)+dRodt(it)*dt;
    dIodt(it)=-dSodt(it)-dRodt(it)-b*I(it-1);
    I(it)=I(it-1)+dIodt(it)*dt;
end
L=(S0+I0+R0)-(S+I+R);
%plot(t,S)
%axis([0 tmax 0 popscale])
%xlabel('time in days')
%ylabel('Number Susceptible')
%title('Epidemic simulation of NYC from near start')
plot(t,I)
axis([0 tmax, 0 popscale])
xlabel('time in days')
ylabel('Number Infected')
title('Epidemic simulation of NYC from near start')
%plot(t,R)
%axis([0 tmax 0 popscale])
%xlabel('time in days')
%ylabel('Number Recovered')
%title('Epidemic simulation of NYC from near start')
popscale=500000
plot(t,L)
axis([0 tmax, 0 popscale])
xlabel('time in days')
ylabel('Number Lost')
title('Epidemic simulation of NYC from near start')

Answer 1

[Star Strider]

Change the for loop to:

for it=2:itmax
    dSodt(it)=-r*S(it-1)*I(it-1);
    S(it)=S(it-1)+dSodt(it)*dt;
    dRodt(it)=a*I(it-1);
    R(it)=R(it-1)+dRodt(it)*dt;
    dIodt(it)=-dSodt(it)-dRodt(it)-b*I(it-1);
    I(it)=I(it-1)+dIodt(it)*dt;
end

and it works!

The problem was the '+1'.

.

[Gregory Mendes]

I tried that. I got the same error.

[Star Strider]

I tried it and it worked.

Try this —

% Equations : dS/dt = -r S I
%             dR/dt = a I
%             dI/dt = -dS/dt - dR/dt - b I
% time measured in days
%S=susceptibles , R=recovereds, I=infecteds.
%             L=(S+R+I)(0)- (S+I+R)(t)
dt= 1.3 %time change

dt = 1.3000

%r=1e-7
r=5e-8

r = 5.0000e-08

a=0.05

a = 0.0500

%b=a*0.01
b=a*0.04

b = 0.0020

S0=8419000.

S0 = 8419000

R0=0

R0 = 0

I0=100

I0 = 100

tmax=120 %number of days

tmax = 120

popscale=8419000 %population scale for graphing

popscale = 8419000

t=0:dt:tmax ;
S(1)=S0;
R(1)=R0;
I(1)=I0;
itmax=ceil(tmax/dt)

itmax = 93

for it=2:itmax
    dSodt(it)=-r*S(it-1)*I(it-1);
    S(it)=S(it-1)+dSodt(it)*dt;
    dRodt(it)=a*I(it-1);
    R(it)=R(it-1)+dRodt(it)*dt;
    dIodt(it)=-dSodt(it)-dRodt(it)-b*I(it-1);
    I(it)=I(it-1)+dIodt(it)*dt;
end
L=(S0+I0+R0)-(S+I+R);
%plot(t,S)
%axis([0 tmax 0 popscale])
%xlabel('time in days')
%ylabel('Number Susceptible')
%title('Epidemic simulation of NYC from near start')
plot(t,I)
axis([0 tmax, 0 popscale])
xlabel('time in days')
ylabel('Number Infected')
title('Epidemic simulation of NYC from near start')

%plot(t,R)
%axis([0 tmax 0 popscale])
%xlabel('time in days')
%ylabel('Number Recovered')
%title('Epidemic simulation of NYC from near start')
popscale=500000

popscale = 500000

plot(t,L)
axis([0 tmax, 0 popscale])
xlabel('time in days')
ylabel('Number Lost')
title('Epidemic simulation of NYC from near start')

.

[Gregory Mendes]

I did all of the edits, tested it out myself. Removed code and re-added it to see if there was an issue outside of it.

It still ends up giving me the same error:

Error using plot

Vectors must be the same length.

Error in epidemic2 (line 38)

plot(t,I)

[Walter Roberson]

you must have initialized t or I to a different size.

[Star Strider]

@Walter Roberson — Thank you!

@Gregory Mendes — The code you are having problems with is obviously not the code you posted.

.