Index in position 2 exceeds array bounds (must not exceed 1).

Hi,

this is part of my code and I have the problem at this line : Dmet(t,b)= min(I(t,b),D(t)- symsum(Dmet(t,b),a,1,b-1)) .

Maybe it is a stupid thing but I don't know how to fix it. Thanks!

for b=1:9
            if b==1
                Dmet(t,b)=min(I(t,b),D(t));       %Dmet(t) is the fraction of the total demand met with batch 1
                Dleft(t,b)=D(t)-Dmet(t,b);        %Dleft(t) is the fraction of the total demand that is not met yet and it will be with batches other than 1
            else 
                Dmet(t,b)= min(I(t,b),D(t)- symsum(Dmet(t,b),a,1,b-1)) ;
                Dleft(t,b)=D(t)-symsum(Dmet(t,b),a,1,b);
            end
        end

[Eleanor Betton]

Can you define I and t?

[Margherita Premoli]

I is the inventory at time t of batch b

t is the time in days (t=1:T and T=365)

This part of the code in insiede another for loop for t=1:T

and D(t) is the total demand of one day

Answer 1

[Shashwat Bajpai]

The problem maybe in the way Dmet is being set in the "if" condition ot the I variable maybe a column vector and thus is not taking b>1. Similarly if Dmet is column vector it won't be able to access (t,b). I would suggest add a breakpoint on the line generating the error and check the dimensions of the variables in use.

Hope this Helps!

[Margherita Premoli]

This is the previous part of the code. I think that I is defined as a matrix but I am not sure about Dmet. In case, how should I define it?

Thank you so much.

N=10000;

T=365;

S=67 ;

for run=1:N

I(1,:)=zeros(1,9) ;

%DEMAND

D=gamrnd(49.6,1,[1 T]) ; %365 random numbers with gamma distribution

D=D.';

for t=1:T

%PLACE THE ORDER AT THE BEGINNING OF THE DAY

Q(t)=S-sum(I(t,:)); %ordered boxes at time t that will end in the batch 1 of the day after

%MEETING THE DEMAND

for b=1:9

if b==1

Dmet(t,b)=min(I(t,b),D(t)); %Dmet(t) is the fraction of the total demand met with batch 1

Dleft(t,b)=D(t)-Dmet(t,b); %Dleft(t) is the fraction of the total demand that is not met yet

else

Dmet(t,b)= min(I(t,b),D(t)- symsum(Dmet(t,b),a,1,b-1)) ;

Dleft(t,b)=D(t)-symsum(Dmet(t,b),a,1,b);

end

end

[Shashwat Bajpai]

Dmet is being initialized a scalar value and thus you get the error. This is happening because in the if statement minimum of I(t,b) and D(t) is '0'. I would suggest pre-allocating Dmet to the required size so that the error does not occur.

[Margherita Premoli]

Thanks, at least I understood why it happens!

The problem is that I do not know how to pre-allocate Dmet because demand met of day 1 ca be met only with batch 1, demand of day 2 with batches 1 and 2, ecc up to day 9 when all the batches have some products in them. From day 9 on, all the batches can be used to met the demand.

How can tell this to Matlab?

Thanks again for your time

Answer 2

[Shashwat Bajpai]

I've made some changes to the code you sent. Please take a look:

N=10000;
T=365;
S=67 ;
for run=1:N
    I(1,:)=zeros(1,365) ;
    %DEMAND
    D=gamrnd(49.6,1,[1 T]) ;    %365 random numbers with gamma distribution
    D=D.';
    Dmet=zeros(1,365);
    syms a;
    for t=1:T
        %PLACE THE ORDER AT THE BEGINNING OF THE DAY
        Q(t)=S-sum(I(t));     %ordered boxes at time t that will end in the batch 1 of the day after
        %MEETING THE DEMAND
        for b=1:9
            if b==1
                Dmet(t,b)=min(I(b),D(t));       %Dmet(t) is the fraction of the total demand met with batch 1
                Dleft(t,b)=D(t)-Dmet(t,b);        %Dleft(t) is the fraction of the total demand that is not met yet
            else
                Dmet(t,b)= min(I(b),D(t)- symsum(Dmet(t,b),a,1,b-1)) ;
                Dleft(t,b)=D(t)-symsum(Dmet(t,b),a,1,b);
            end
        end
    end
end

Since you have initialized I as a row vector you do not need to give to values to access its elements, therfore i changed that. The second for loop runs from t=1:T this will run for 365 times and since you allocated I to be only a 1x9 vector it will run into an error. You also need to define the variable a which i declared as a symbol as you are using symsum. If pre-allocating Dmet doesn't work you can define it as a cell array and convert it back to a matrix after the looping is finally over.

Hope this Helps!

[Margherita Premoli]

Okay thanks a lot for the chages and explanation, now it makes more sense!

Just to be sure about the I variable, there is also the problem similar to Dmet because at the time 1 there will products in the inventory of only the first batch, at time 2 products in batches 1 and 2 and so on till day 9. After that day, the invetory of every batch can have values different than zero. I am not sure or at least I do not know if writing I(1,:)=zeros(1, 365) means that.

And thanks for the last tip, I will try :)

[Margherita Premoli]

and sorry, one more thing! Why is defined Dmet=zeros(1 365) instead of Dmet=zeros(365 1) since I transposed the row vector of D into a column vector? Because the variables Dmet and I are both described by (t,b) not (b,t).

I am sorry but I am reallt strugglin gin understanding Matlab language :(

[Shashwat Bajpai]

 I(1,:)=zeros(1,365) ;

The above statement just pre-allocates the variable so that it doesn't face any issues while execution. Dmet is row vector because the I is a row vector and

min(I(b),D(t))

will give '0' if condition of I is satisfied.

[Margherita Premoli]

Okay, so I do not have to transpose the D right? I mean, should I delete D=D.' ?

Maybe I didn't explain well the I because it is a variable that is defined as the number of products in stock in every batch b for every day t, therefore I thought that the variable I should be written as I(t,b). The same is for Dmet. That is why I transposed the D, so as I will have a matrix with the column vector D (365x1 which means one demand for every day) and the row vector I (1x9 which means that every day there are 9 possible batches). Am I wrong? Should I define a b row vector next to the D column vector and then ask for I(t,b)?

Thansk a lot again! I really appreciate your help