Need Help about this for loop

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BN 2020-2-5

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评论： BN 2020-2-5

Hey all, I have a very simple issue about saving for loop results in the one variable at the end.

I have this code. In the First for loop which is for i =1:6. If you looking at output part (at the end of the code) you can see: SI(sc:end,1)=SI1; I want all sc (for i=1:6) outputs save in the SI (multiple columns). At this time only the results of i=6 saves in the SI.

sc_vect=[1 3 6 12 24 48];
for i=1:6
    sc = sc_vect(i);
% sc: scale of the index (>1, e.g., 3-month SPI or SSI)
n=length(td);
SI=zeros(n,12);
% Compute the SPI for each grid from the prcp or smc data
%For some grid, no observation exist.
if length(td(td>=0))/length(td)~=1
   SI(n,1)=nan;
   else
   % Obtain the prcp and smc for the specified time scale and
   % compute the standarized drought index (for SPI and SSI)
   SI(1:sc-1,1)=nan;
            
   A1=[];
   for i=1:sc,  
   A1=[A1,td(i:length(td)-sc+i)];
   end
   Y=sum(A1,2);
   % Compute the SPI or SSI
    nn=length(Y);
    SI1=zeros(nn,1);
    for k=1:12
    
    d=Y(k:12:nn);
    %compute the empirical probability
    nnn=length(d);
    bp=zeros(nnn,1);
    for i=1:nnn
    bp(i,1)=sum(d(:,1)<=d(i,1));
    end
    y=(bp-0.44)./(nnn+0.12);
    
    SI1(k:12:nn,1)=y;
    end
SI1(:,1)=norminv(SI1(:,1));
%output                   
SI(sc:end,1)=SI1;
end
end

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Ajay Kumar 2020-2-5

编辑：Ajay Kumar 2020-2-5

Rik meant to use debugger to go line by line. Not to run whole code at once.

Put a breakpoint on line 1 and go line by line to see how the variables are storing.

Marcel Kreuzberg 2020-2-5

Yor are using i for the outer loop and two inner loops. Maybe you shuld change index.

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Answer 1

Rik 2020-2-5

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You are reusing i as a loop index multiple times. The mlint also warns you about that. It is a good idea to resolve all warnings mlint gives you, or mark them with the ok pragma (right-click on the orange underlined text and select 'on this line' in the suppress warning menu). That way you can instantly see if an edit caused a new warning.

As for the issue you are describing: the line below resets SI every time the outer loop runs.

SI=zeros(n,12);

You also don't assign any values to the later columns of SI. I suspect you want to have something like this in your code:

SI(sc:end,i)=SI1;
%(assuming you keep using i as a variable and use it as your loop index for the outer loop)

Although it is common in many programming languages, it is generally recommended to avoid i and j as variable names to avoid confusion or bugs caused by interpretation as the imaginary unit.

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BN 2020-2-5

编辑：BN 2020-2-5

在 MATLAB Online 中打开

Abadan.mat

Dear Rik

Thank you for let me know. According to your answer I changed my code to this:

td=Abadan.rrr24;
Date = Abadan.date;
sc_vect=[1 3 6 12 24 48];
for p=1:6
    sc = sc_vect(p);
n=length(td);
SI=zeros(n,1);
% Compute the SPI for each grid from the prcp or smc data
%For some grid, no observation exist.
if length(td(td>=0))/length(td)~=1
   SI(n,1)=nan;
   else
   % Obtain the prcp and smc for the specified time scale and
   % compute the standarized drought index (for SPI and SSI)
   SI(1:sc-1,1)=nan;
       
   A1=[];
   for i=1:sc,  
   A1=[A1,td(i:length(td)-sc+i)];
   end
   Y=sum(A1,2);
   % Compute the SPI or SSI
    nn=length(Y);
    SI1=zeros(nn,1);
    for k=1:12
    
    d=Y(k:12:nn);
    %compute the empirical probability
    nnn=length(d);
    bp=zeros(nnn,1);
    for i=1:nnn
    bp(i,1)=sum(d(:,1)<=d(i,1));
    end
    y=(bp-0.44)./(nnn+0.12);
    
    SI1(k:12:nn,1)=y;
    end
SI1(:,1)=norminv(SI1(:,1));
%output                   
SI(sc:end,p)=SI1;
end
end

But still, after running, the results of i=6 saves in the sixth column of SI and first to the fifth column stay zero.

Do you know what is the problem? I attach my data for you named is Abadan.

Thank you

BN 2020-2-5

在 MATLAB Online 中打开

I think this problem cant solve by matlab, it's very complicated for me so een I don't like I must using this code in order to achive SI3 and SI6 and so on without loop. If anyone can help me in this regard to how make a loop and summerize this code I would be so greatful.

td = Abadan.rrr24;
Date = Abadan.date;
% sc: scale of the index (>1, e.g., 3-month SPI or SSI)
sc=3;
n=length(td);
SI=zeros(n,1);
% Compute the SPI for each grid from the prcp or smc data
%For some grid, no observation exist.
if length(td(td>=0))/length(td)~=1
    SI(n,1)=nan;
else
    % Obtain the prcp and smc for the specified time scale and
    % compute the standarized drought index (for SPI and SSI)
    SI(1:sc-1,1)=nan;
    
    A1=[];
    for i=1:sc,
        A1=[A1,td(i:length(td)-sc+i)];
    end
    Y=sum(A1,2);
    
    % Compute the SPI or SSI
    
    nn=length(Y);
    SI1=zeros(nn,1);
    
    for k=1:12
        
        d=Y(k:12:nn);
        %compute the empirical probability
        nnn=length(d);
        bp=zeros(nnn,1);
        
        for i=1:nnn
            bp(i,1)=sum(d(:,1)<=d(i,1));
        end
        
        y=(bp-0.44)./(nnn+0.12);
        
        SI1(k:12:nn,1)=y;
    end
    
    SI1(:,1)=norminv(SI1(:,1));
    %output
    SI(sc:end,1)=SI1;
end
%plot vector
f=figure(1);clf(f)
plot(Date,SI, 'linewidth',1.5)
xlabel('time step')
ylabel('Standardized Precipitation Index 1')
xticks(Date(1:12:end))
ax=gca;
set(ax,'XTickLabelRotation',90)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% %%SPI 6month
%% main code
% sample input
sc=6;
n=length(td);
SI6=zeros(n,1);
% Compute the SPI for each grid from the prcp or smc data
%For some grid, no observation exist.
if length(td(td>=0))/length(td)~=1
    SI6(n,1)=nan;
else
    % Obtain the prcp and smc for the specified time scale and
    % compute the standarized drought index (for SPI and SSI)
    SI6(1:sc-1,1)=nan;
    
    A1=[];
    for i=1:sc,
        A1=[A1,td(i:length(td)-sc+i)];
    end
    Y=sum(A1,2);
    
    % Compute the SPI or SSI
    
    nn=length(Y);
    SI1=zeros(nn,1);
    
    for k=1:12
        
        d=Y(k:12:nn);
        %compute the empirical probability
        nnn=length(d);
        bp=zeros(nnn,1);
        
        for i=1:nnn
            bp(i,1)=sum(d(:,1)<=d(i,1));
        end
        
        y=(bp-0.44)./(nnn+0.12);
        
        SI1(k:12:nn,1)=y;
    end
    
    SI1(:,1)=norminv(SI1(:,1));
    %output
    SI6(sc:end,1)=SI1;
end
%plot vector
f=figure(1);clf(f)
plot(Date,SI6, 'linewidth',1.5)
xlabel('time step')
ylabel('Standardized Precipitation Index 6')
xticks(Date(1:12:end))
ax=gca;
set(ax,'XTickLabelRotation',90)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% SAME PROCESS FOR ALL 6 IS THAT I NEED
%% THEN I CAN USE FIRST COLUMN OF EACH SI TO MAKE A INTEGRATED 6 COLUMNS TABLE

Rik 2020-2-5

在 MATLAB Online 中打开

You keep clearing your output:

SI=zeros(n,1);

You should do something like this:

td=Abadan.rrr24;
Date = Abadan.date;
sc_vect=[1 3 6 12 24 48];
n=length(td);
SI=zeros(n,numel(sc_vect));
for p=1:numel(sc_vect)
    sc = sc_vect(p);

BN 2020-2-5

Thank you, After doing that, it's worked.

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