Nested FOR Loop Help

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James 2015-7-7

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编辑： bio lim 2015-7-8

I would like to vary the value of a parameter in my model that was originally a static variable by using a nested FOR loop. I am testing the model sensitivity to the parameter, and I would eventually like to vary two variables using another FOR loop. If this is not the best way to go about this, I am happy to hear suggestions. I want the second FOR loop to run all iterations using the first value in the first FOR loop and once it is done I want the second FOR loop to run the second value.

When I run the code I get this ERROR: Attempted to access uplift_rate(2); index out of bounds because numel(uplift_rate)=1.

My code looks like this:

uplift_rate = [1e-2, 2e-2]
for i=1:numel(nColumns);
      uplift_rate_i = uplift_rate(i)
           for j=1:nSteps;
              y = y+(uplift_rate_i(j)*dt); %new height
              % calculate water depth, h1
              h=SL(nSteps-j+1)-y;
           end
end

Thank you in advance for the help.

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Stephen23 2015-7-8

Note that you should avoid using i and j for variable names (e.g. loop variables), as these are both names of the inbuilt imaginary unit.

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Answer 1

bio lim 2015-7-8

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I don't really understand your code. What is the purpose of the first loop? I think every time it loops ( i = 1 : numel(nColums) it is overwriting the scalar in uplift_rate_i, and that i is not indexing. It is part of your array name. Therefore, the second loop is also not going to work because,

numel(uplift_rate_i) = 1

uplift_rate_i(j) for j ~=1 don't exist.

I think you should upload your program.

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bio lim 2015-7-8

编辑：bio lim 2015-7-8

在 MATLAB Online 中打开

Initial Conditions:

dt=100; 
tmax = 1400000; 
t=0:dt:tmax;
nSteps=numel(t);

Your first loop is as follows.

for i=1:numel(nColumns);
    uplift_rate_i = uplift_rate(i)

In here, nColumns = 2. What you are doing here can already be obtained from the indexing, and therefore I don't understand why you are assigning a variable to the elements. In other words, I think this loop is not necessary. You can simply use uplift_rate(1) and uplift_rate(2).

For the second loop

 for j=1:nSteps;
        y = y+(uplift_rate_i(j)*dt); 
        h=SL(nSteps-j+1)-y;
 end

From your initial condition, you can see that nSteps = 14001, which is far larger than length(uplift_rate) = 2. Therefore, index more than 2 doesn't exist.

What I think is that you might have defined your uplift_rate matrix wrong from the start.

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