Array indexing, matrix indexing

Question

Irfanullah Khan 2019-9-11

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关闭： Stephen23 2019-9-11

采纳的回答： Bob Thompson

n=6;

h(:,:,1) = [0 1 2 1 2 3;

1 0 1 1 2 2;

2 1 0 2 1 1;

1 1 2 0 1 2;

2 2 1 1 0 1;

3 2 1 2 1 0];

h(:,:,2) = [0 2 3 2 3 4;

2 0 3 2 3 3;

3 3 0 3 2 2;

2 2 3 0 3 3;

3 3 2 3 0 2;

4 3 2 3 2 0];

for i = 1:n

for j = 1:n

if i ==n && j == n

fprintf('%d %d %d %d;\n', i, j, h(i,j,1),h(i,j,2));

else

fprintf('%d %d %d %d\n', i, j, h(i,j,1),h(i,j,2));

end

it give me the result like

1 1 0 0

1 2 1 2

1 3 2 3

1 4 1 2

1 5 2 3

1 6 3 4

2 1 1 2

2 2 0 0

2 3 1 3

.....

6 6 0 0;

..........................

i want to get expected result like

1 1 1

1 2 1

1 3 1

-----

6 6 1

1 1 2

1 2 2

1 3 2

----

2 1 2

2 2 2

----

6 6 2

the actual results print the value of i, j and h1(i,j) and h2(i,j) but actually i dont want to print the value of h1,h2 with respect to i, j but i want to print the results i,j and the index of h. Kindly guide me in this regards,

thank you

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Answer 1

Bob Thompson 2019-9-11

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Personally, I don't think the loops are necessary. It's not much cleaner looking than the loops, but I suspect it will run more quickly. Because you're just looking to produce index values, then you really don't need to involve h at all during this stage.

p = 1:n;
p = repmat(p,n,1);
p = reshape(p,[],1);
q = 1:n;
q = repmat(q,1,n);
p = [p q'];
p = repmat(p,2,1);
p(:,3) = [repmat(1,n^2,1);repmat(2,n^2,1)];
fprintf('%d %d %d\n',p');

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Irfanullah Khan 2019-9-11

thank you for your time, consideration and prompt response. Actually i am writing a code in GLPK and have already mentioned the h in whole code. i have 2 different path which has been showing by h(:,:,1) and h(:,:,2). i need to print the the dimension of h insteady of the value of h with the value of i and j. Kindly modify my above code which show me the results like

1 1 1

1 2 1

1 3 1

-----

6 6 1

1 1 2

1 2 2

1 3 2

----

2 1 2

2 2 2

----

6 6 2

Thank you so much. i am very thankfull for your this act of kindness. thanking you

Bob Thompson 2019-9-11

Just to clarify, are you asking on a MATLAB forum for a non-MATLAB code question? I don't know that you're going to get very good answers that way.

I am not familiar with the GLPK language or syntax, but if you want a loop version to create the matrices I indicated before then you can use something like the following:

for i = 1:2
    for j = 1:n
        for k = 1:n
            fprintf('%d %d %d\n', j , k , i);
        end
    end
end

Answer 2

Andrey Kiselnikov 2019-9-11

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Hi, it looks like you are still writing code on something like c or pascal using MATLAB syntax. First of all, you should change your mind, MATLAB was designed for matrix manipulations and you don't need to use nested cycles!

Good reference for this theme: https://www.mathworks.com/help/matlab/math/basic-matrix-operations.html

Good set of beginners exercises: https://www.mathworks.com/matlabcentral/cody/problems?sort=&term=group%3A%22Matrix+Manipulation+I%22

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Irfanullah Khan 2019-9-11

yes, you are right. i am using GLPK to write the code for optimization problem. Kindly modify the above code as expecting result. thanking you

Answer 3

Amit 2019-9-11

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编辑：Amit 2019-9-11

Hi, not sure why you are using the if condition as the statements are same in if and else block..

And use one more loop to get the dim of h if you want to do it in same manner : hope this will help you

n=6;

h(:,:,1) = [0 1 2 1 2 3;

1 0 1 1 2 2;

2 1 0 2 1 1;

1 1 2 0 1 2;

2 2 1 1 0 1;

3 2 1 2 1 0];

h(:,:,2) = [0 2 3 2 3 4;

2 0 3 2 3 3;

3 3 0 3 2 2;

2 2 3 0 3 3;

3 3 2 3 0 2;

4 3 2 3 2 0];

for dim = 1:size(h,3)

for i = 1:n

for j = 1:n

fprintf('%d %d %d \n', i, j, dim);

end