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Thread: inverting rows and lines of a matrix

  1. #1
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    Default inverting rows and lines of a matrix

    Hi everyone, I'd like to create a program in which all rows and columns of a given matrix are inverted. The matrix elements are objects Bin<Double,Integer>, where Double is the value, Integer is the priority (that can be 0 or 1). When i reorder the matrix, I have to replace the entire Objects
    For example :

    Schermata 2019-10-31 alle 06.35.18.png

    I've thought something like this, but i don't think it's quite correct:

    for(int i=0;i<matrix.length;i++){
    for(int k=0;k<matrix.length;k--) {
    for(int j=0;j<matrix.length;j++){
    for (int s = 0; s < matrix.length; s--) {

    Bin<Double,Integer> element = new Bin<>();

    element= mat_simmetrica[i][j];
    mat_simmetrica[i][j]=mat_simmetrica[k][s];
    mat_simmetrica[k][s]=element;

    }
    j++;
    }

    }
    i++;
    }

  2. #2
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    Default Re: inverting rows and lines of a matrix

    i don't think it's quite correct:
    Please explain. Post the program's current output and add comments saying what is wrong with it.

    Please edit your post and wrap your code with code tags:

    [code]
    **YOUR CODE GOES HERE**
    [/code]

    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: inverting rows and lines of a matrix

    Actually it doesn't work, It gives me: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1

    The idea is to switch each element with his opposite, so I've thought to do 4 cycles E(i,j) <-> E(k,s)

    K=2

    E(0,0) <-> E(k,k)
    E(0,1)<->E(k,k-1)
    E(0,2)<->E(k,k-2)

    E(1,0)->E(k-1,k)
    E(1,1)->E(k-1,k-1)
    E(1,2)->E(k-1,k-2)

    E(2,0)->E(k-2,k)
    E(2,1)->E(k-2,k-1)
    E(2,2)->E(k-2,k-2)

            for(int i=0;i<mat_simmetrica.length;i++){
                    for(int k=mat_simmetrica.length;k>0;k--) {
                        for(int j=0;j<mat_simmetrica.length;j++){
                        for (int s = mat_simmetrica.length; s > 0; s--) {
     
                            Bin<Double,Integer> element = new Bin<>();
     
                            element= mat_simmetrica[i][j];
                            mat_simmetrica[i][j]=mat_simmetrica[k][s];
                            mat_simmetrica[k][s]=element;
     
                        }
                        j++;
                    }
     
                }
               i++;
            }
    Last edited by mikoile; October 31st, 2019 at 09:45 AM.

  4. #4
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    Default Re: inverting rows and lines of a matrix

    Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
    What variable has the -1?

    Where does the code use a negative index? Zero minus 1 = -1
    The code should not subtract from a 0 index
    If you don't understand my answer, don't ignore it, ask a question.

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