Array indexing, matrix indexing

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Asked by Irfanullah Khan on 11 Sep 2019

Latest activity Closed by Stephen Cobeldick on 11 Sep 2019

Accepted Answer by Bob Nbob

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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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3 Answers

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Answer by Bob Nbob on 11 Sep 2019

Accepted Answer

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');

2 Comments

Irfanullah Khan on 11 Sep 2019

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 Nbob on 11 Sep 2019

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

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Answer by Andrey Kiselnikov on 11 Sep 2019

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

1 Comment

Irfanullah Khan on 11 Sep 2019

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

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Answer by Amit on 11 Sep 2019

Edited by Amit on 11 Sep 2019

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

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Array indexing, matrix indexing

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