If statement for cells

Question

MarshallSc 2021-7-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/876088-if-statement-for-cells

评论： Star Strider 2021-7-12

采纳的回答： Star Strider

在 MATLAB Online 中打开

Hi, I have 3 different cell arrays like below - same size (let's call them A, B and C):

That I need to evaluate in an if statement in a for loop. But the final result gives me several empty numeric array in couple of the cells. The code is:

for i=1:4
    for j=1:4
        for k=1:10
        for r=1:10
              if ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))<1) && ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))<1)
              A_num{i,j}{k,r}='Point is stable: Category 1 is assigned';
              elseif ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))>1) && ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))>1)
              A_num{i,j}{k,r}='Point is unstable';
              end
        end
        end
    end
end

For example, one of the cell array result is like bleow:

I checked all the components of the original cell arrays and none of them are zero or inf. Am I doing something wrong here?

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Answer 1

Star Strider 2021-7-11

2
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https://ww2.mathworks.cn/matlabcentral/answers/876088-if-statement-for-cells#answer_744173

The && are ‘short circuit’ AND operators. The second expression (after the &&) will not be evaluated if the first expression is false.

If you want to evaluate both of them, just use & instead.

.

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Star Strider 2021-7-11

在 MATLAB Online 中打开

My pleasure!

Something is clearly wrong with the logic.

I suggest that you break out the comparison statements into separate statements to check to be sure that they are doing what you want them to do. Just add the separate staements before the if block. (I call them ‘Test1’ and ‘Test2’ here.) It will not be necessary to change the code otherwise.

Example —

for i=1:4
    for j=1:4
        for k=1:10
        for r=1:10
            Test1 = ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))<1)
            Test2 = ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))<1)
              if ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))<1) && ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))<1)
              A_num{i,j}{k,r}='Point is stable: Category 1 is assigned';
              elseif ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))>1) && ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))>1)
              A_num{i,j}{k,r}='Point is unstable';
              if abs(C{i,j}(k,r))>abs(B{i,j}(k,r))
                 M{i,j}(k,r)=abs(C{i,j}(k,r));
                 else
                 M{i,j}(k,r)=abs(B{i,j}(k,r));
              end
              end
        end
        end
    end
end

That should tell you if they are doing what you want them to do. You can slso subscript them:

            Test1(k,r) = ((abs(A{i,j}(k,r)))/(abs(C{i,j}(k,r)))<1);
            Test2(k,r) = ((abs(A{i,j}(k,r)))/(abs(B{i,j}(k,r)))<1);

so you can look at them in detail later to see how they compare to what you want them to do. (This is how I always solve such logic problems in code I write.)

I believe the comparison ‘<1’ (or ‘>1’ in the subsequent test) should be outside all the nested parentheses, however since I do not understand what you are doing, I cannot be certain of that.

.

Star Strider 2021-7-11

在 MATLAB Online 中打开

I do not see anything wrong with the logic itself, however you may want to use or,| rather than and,& in the comparison:

Compare the results of using ‘&’ and ‘|’ in ‘Test12’ here:

LD1 = load('A.mat');
A = LD1.Kappa_x;
LD2 = load('B.mat');
B = LD2.KappaShort_x;
LD3 = load('C.mat');
C = LD3.KappaLong_x;
for i = 1:4
    for j = 1:4
        Quot1{i,j} = abs(A{i,j})./abs(C{i,j});
        Quot2{i,j} = abs(A{i,j})./abs(B{i,j});
    end
end
figure
[x,y] = ndgrid(1:10);
k = 0;
for i = 1:4
    for j = 1:4
        k = k + 1;
        Test1 = Quot1{i,j}<1;
        Test2 = Quot2{i,j}<1;
        Test12 = Test1 | Test2;
        subplot(4,4,k)
        plot3(x, y, Test1, '+b')
        hold on
        plot3(x, y, Test2, 'xr')
        plot3(x, y, Test12, 'og')
        hold off
        grid
        view(-40,10)
        zlim([-0.5 1.5])
        title(sprintf('i=%d, j=%d',i,j))
        set(gca, 'ZTick',[0 1], 'ZTickLabel',["F","T"])
    end
end
pos = get(gcf,'Position');
set(gcf, 'Position',pos+[0  -500  500  500])

I always encourage plotting if possible, since it is an easy way to see what the code is actually doing:

.

MarshallSc 2021-7-12

Thank you so much buddy. This is an interesting testing method that I will use. Thank you again!

Star Strider 2021-7-12

My pleasure!

If my Answer helped you solve your problem, please Accept it!

.

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If statement for cells

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