how to fix a nested for loop

Question

Vert 2014-10-20

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https://ww2.mathworks.cn/matlabcentral/answers/159318-how-to-fix-a-nested-for-loop

回答： Orion 2014-10-21

I am trying to run through several values for two of the variables in a function. The function worked fine when I gave it individual values for K and Smax but I can't get the loop to work.

I keep getting one of two errors, no matter what I've tried: Subscripted assignment dimension mismatch. -OR- Attempted to access Storage(2,2); index out of bounds because size(Storage)=[1,2].

Below is the code I'm working on and the data file is attached.

Define parameter space

K_min = 0.01; K_max = 1;
Smax_min = 10; Smax_max = 500;
stride = 10; % or 50 or 100
K = linspace(K_min,K_max,stride); % vector of k
K = repmat(K,[stride,1]); %space of k
Smax = linspace(Smax_min,Smax_max,stride);
Smax = repmat(Smax,[stride,1]);

Run Model

Storage = [Precipmmday(1) 0];
for Smax = 1:stride;
    for K = 1:stride;
        for k1 = 2:length(Precipmmday)
            Storage = [Precipmmday(1) 0];
            Baseflow = [Precipmmday(1) 0 ];
                Baseflow (k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*K];
                Storage(k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*(1-K)];
                    end
                end
        end
            ModelStorage = Storage;
            SynthStorage (:,1) =[];
              ModelSpill=ModelStorage - Smax;
              ModelSpill(ModelSpill<0)=0;
              ModelStorage(ModelStorage>Smax)=Smax;
              ModelBaseflow = Baseflow;
              ModelBaseflow (:,1) = [];
              ModelOutflow = ModelBaseflow + ModelSpill;

I know it's clunky, I'm new to MatLab. It doesn't have to be pretty, I just want it to work!

Any help appreciated.

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Answer 1

Orion 2014-10-20

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Hi Rosa,

- the variable Precipmmday is not defined in your code.

- you should reedit your question with the code part formatted, so we can check it more easily.

- about the error you get Attempted to access Storage(2,2); index out of bounds because size(Storage)=[1,2].

in your loop, at every iteration, you redefine

Storage = [Precipmmday(1) 0];

so Storage is a row vector with 2 elements, and then you do

Baseflow (k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*K];

if k1 == 2, it works, but at the second iteration, k1 = 3, and so you are trying to access the second row of a one row vector, which gives you that error.

also, there are the two consecutive lines :

              Baseflow = [Precipmmday(1) 0 ];
              Baseflow (k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*K];

the first line will reset the variable Baseflow at each iteration, which is probably not what you want

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Vert 2014-10-20

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Thank you for replying. I re-formatted it.

Yes, I think I see what you mean, but I don't know how to fix the dimensions problem. I had used that code earlier to calculate the variables for one set of parameters and it worked, but now trying to run through multiple parameter sets, I can't figure it out.

Below is the rest of what I was doing, if that helps.

Basic Variables

TimeDay = 1:1088;
TimeDay = TimeDay';
%Precipitation Time Series
%
plot(TimeDay, Precipmmday)
xlabel('Time (day)');
ylabel('Rainfall (mm/day)');
title('Precipitation');

No Spill Scenario Storage where k=0.3; Smax=100

SynthK=0.3;
SynthSmax=100;
Storage = [Precipmmday(1) 0];
Baseflow = [Precipmmday(1) 0 ];
for k1 = 2:length(Precipmmday)
    Baseflow (k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*SynthK];
    Storage(k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*(1-SynthK)];    
end
SynthStorage = Storage;
SynthStorage (:,1) =[];
SynthSpill=SynthStorage - SynthSmax;
   SynthSpill(SynthSpill<0)=0;
SynthStorage(SynthStorage>SynthSmax)=SynthSmax;
SynthBaseflow = Baseflow;
SynthBaseflow (:,1) = [];
SynthOutflow = SynthBaseflow + SynthSpill;

Define parameter space

K_min = 0.01; K_max = 1;
Smax_min = 10; Smax_max = 500;
stride = 10; % or 50 or 100
K = linspace(K_min,K_max,stride); % vector of k
K = repmat(K,[stride,1]); %space of k
Smax = linspace(Smax_min,Smax_max,stride);
Smax = repmat(Smax,[stride,1]);

Run Model

for Smax = 1:stride;
    for K = 1:stride;
                Baseflow (k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*K];
                Storage(k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*(1-K)];
                end
        end
            ModelStorage = Storage;
            SynthStorage (:,1) =[];
              ModelSpill=ModelStorage - Smax;
              ModelSpill(ModelSpill<0)=0;
              ModelStorage(ModelStorage>Smax)=Smax;
              ModelBaseflow = Baseflow;
              ModelBaseflow (:,1) = [];
              ModelOutflow = ModelBaseflow + ModelSpill;

Thanks again for your help.

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Answer 2

Orion 2014-10-20

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your double loop is not using the index Smax. also, k1 is fixed in this double loop.

this doesn't mean so much ?

(and Precipmmday still not defined.)

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Vert 2014-10-20

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I cleaned it up a bit and tried to address what you're saying, but I can't get it to run. Can you give any suggestions about what I should do to fix the issues? (I see what you are saying but this is my first time in MatLab and I can't figure out how to actually address the problems)

My goal is for it to repeat through every combination of K and Smax.

Run Model

  Storage = [Precipmmday(1) 0];
  Baseflow = [Precipmmday(1) 0];
  for Smax = linspace(10,500,10);
      Smax = repmat(Smax,10,1);
      for K = linspace(0.01,1,10);
          K = repmat(K,10,1);
          for k1 = 2:length(Precipmmday)
                  Baseflow(k1,:)  = [(Storage(k1-1,2)+Precipmmday(k1-1))*K];
                  Storage(k1,:) = [(Storage(k1-1,2)+Precipmmday(k1-1))*(1-K)];
          end
              ModelStorage = Storage;
              ModelSpill=ModelStorage - Smax;
              ModelSpill(ModelSpill<0)=0;
              ModelStorage(ModelStorage>Smax)=Smax;
              ModelBaseflow = Baseflow;
              ModelOutflow = ModelBaseflow + ModelSpill;
      end
  end

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Answer 3

Orion 2014-10-21

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this code just can't work because you're redefining the index variable Smax ans K inside the loops

for Smax = linspace(10,500,10);
      Smax = repmat(Smax,10,1);

You must never do that (you will lost control of your code).

I don't know the problem you're studying. But here's what you should do to achieve your goal.

Write properly your algorithm on a paper (not the code, just the idea) and identify which variable must be a scalar, a vector, a matrix.

because, when you do Smax = linspace(10,500,10); , you're creating a vector, but then Smax = repmat(Smax,10,1), you're creating a matrix, in which all lines are the same (is there a real meaning to this), and so on for K.

So, what do you you need to create in the end : vector or matrix (ModelBaseflow, ModelOutflow ,...) ?

According your need, you will create 1 or loops, and manipulate differents index.