MATLAB: For loop preallocation warning

debugMATLABpreallocationspeed up

Hello all,
Even the code works properly, I get a warning flag that advice me to preallocate all of the variables that I am accumulating during the execution of the code, do you know how to deal with this issue?, in order to debug and make faster the execution of the code.
Thanks in advance!.
%To simulate the 12 months at one click
current_path = pwd;
tic
load DATA_HILL.mat
PV_MAX_=[];
DEV_PV_=[];
SOC_=[];
month_=[];
PV_irr_=[];
Dev_2_=[];
z=zeros(12,6);
for month_number=1:12
    
    sim('HILL_V2.slx')
    disp(month_number);
    
    bdclose('HILL_V2.slx');
    
    %%%%%%
    %%%%Data upload
    load Power_PV.mat
    load SOC.mat
    load month
    load Irr
    %%%Results format
    format Eng
    %%%%Variables analysed in this study case
    PV_MAX=max(Power_PV);
    %

    DEV_PV= (PV_MAX/189000)*100;
    %
    SOC= min(SOC);
    m=mean(month);
    PV_irr=max(Irr)*189;
    Dev_2=(1-(PV_MAX/PV_irr))*100;
    
    % % % % All of the accumulated variables in the for loop
    PV_MAX_=[PV_MAX; PV_MAX_];
    DEV_PV_=[DEV_PV; DEV_PV_];
    SOC_=[SOC; SOC_];
    month_=[m; month_];
    PV_irr_=[PV_irr; PV_irr_];
    Dev_2_=[Dev_2; Dev_2_];
    
    cd(current_path);
end
A=flip([month_ SOC_ PV_MAX_ DEV_PV_ PV_irr_ Dev_2_].*z);
%%%%To creat a table in order to represent the results of the simulation
% RowName={'Month', 'SOC_min(%)', 'PV_MAX (kW)', 'DEV_PV (%)', 'PV_irr (kW)', 'Dev_2 (%)'};
LastName=flip({'Jan';'Feb';'Mar';'Apr';'May';'Jun';'Jul';'Aug';'Sep';'Oct';'Nov';'Dec'});
T=table(month_, SOC_, PV_MAX_, DEV_PV_, PV_irr_, Dev_2_,...
     'RowName', LastName);
disp(T)
toc

Best Answer

Here is a general way.
If you use the following codes, you will get a warnings
x = []
for i = 1:10
    x(i) = sin(i); % sin(i) used as example

end
% or
x = []
for i = 1:10
    x = [x sin(i)]
end
You can solve the warning by pre-allocating and use indexing to assign elements
x = zeros(1, 10)
for i = 1:10
    x(i) = sin(i); % sin(i) used as example
end
For your code, following will work
%To simulate the 12 months at one click
current_path = pwd;
tic
load DATA_HILL.mat
PV_MAX_=zeros(12,1);
DEV_PV_=zeros(12,1);
SOC_=zeros(12,1);
month_=zeros(12,1);
PV_irr_=zeros(12,1);
Dev_2_=zeros(12,1);
z=zeros(12,6);
for month_number=1:12
    
    sim('HILL_V2.slx')
    disp(month_number);
    
    bdclose('HILL_V2.slx');
    
    %%%%%%
    %%%%Data upload
    load Power_PV.mat
    load SOC.mat
    load month
    load Irr
    %%%Results format
    format Eng
    %%%%Variables analysed in this study case
    PV_MAX=max(Power_PV);
    %

    DEV_PV= (PV_MAX/189000)*100;
    %
    SOC= min(SOC);
    m=mean(month);
    PV_irr=max(Irr)*189;
    Dev_2=(1-(PV_MAX/PV_irr))*100;
    
    % % % % All of the accumulated variables in the for loop
    PV_MAX_(i)=PV_MAX
    DEV_PV_(i)=DEV_PV;
    SOC_(i)=SOC;
    month_(i)=m;
    PV_irr_(i)=PV_irr;
    Dev_2_(i)=Dev_2;
    
    cd(current_path);
end
A=flip([month_ SOC_ PV_MAX_ DEV_PV_ PV_irr_ Dev_2_].*z);
%%%%To creat a table in order to represent the results of the simulation
% RowName={'Month', 'SOC_min(%)', 'PV_MAX (kW)', 'DEV_PV (%)', 'PV_irr (kW)', 'Dev_2 (%)'};
LastName=flip({'Jan';'Feb';'Mar';'Apr';'May';'Jun';'Jul';'Aug';'Sep';'Oct';'Nov';'Dec'});
T=table(month_, SOC_, PV_MAX_, DEV_PV_, PV_irr_, Dev_2_,...
     'RowName', LastName);
disp(T)
toc
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