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

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Margherita Premoli
评论： Margherita Premoli 2020-2-13
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
  2 个评论
Margherita Premoli
Margherita Premoli 2020-2-6
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

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回答（2 个）

Shashwat Bajpai
Shashwat Bajpai 2020-2-10
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!
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Shashwat Bajpai
Shashwat Bajpai 2020-2-11
编辑：Shashwat Bajpai 2020-2-11
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
Margherita Premoli 2020-2-11
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

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Shashwat Bajpai
Shashwat Bajpai 2020-2-12
编辑：Shashwat Bajpai 2020-2-12
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!
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Shashwat Bajpai
Shashwat Bajpai 2020-2-13
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
Margherita Premoli 2020-2-13
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

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