Multiplication matrix by the matrix transposed in C language

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I'm new to programming and I'm trying to make a C language program that multiplies a 3x3 array by its transpose and prints the result . I'm having trouble creating the algorithm of multiplication between the matrix by its transpose. Any help will be gladly given.

Follow the code:

libraries used ( stdio.h and stdlib.h ) 

int main(){

int mat[3][3], mat_transposta[3][3], mat_resultado[3][3];
int i, j;

// leitura matriz
for(i = 0; i < 3; i++){
    for(j = 0; j < 3; j++){
        scanf("%d",&mat[i][j]);
    }
    for(i = 0; i < 3; i++){
        for(j = 0; j < 3; j++){
            mat_transposta[i][j] = mat[j][i]; // transformação matriz principal p/ transposta (FUNCIONANDO)
        }
    }
        for(i = 0; i < 3; i++){
            for(j = 0; j < 3; j++){
                mat[i][j] *= mat_transposta[i][j];// multiplicação da matriz pela sua transposta correspondente

            }
        }

            for (i = 0; i < 3; i++){
                for (j = 0; j < 3; j++){
                    printf("%d\t", mat_resultado[i][j]); // impressão matriz resultado (A SAÍDA TEM QUE SER NESSE FORMATO)
                }
                printf("\n");
            }
return 0;
}

So the X of the question is to solve the following algorithm ( which is logically wrong, I know ). I was unable to create a pattern (i and j) for multiplication, which could be implemented as the minimum use of for commands to perform this multiplication. 

for(i = 0; i < 3; i++){
            for(j = 0; j < 3; j++){
                mat[i][j] *= mat_transposta[i][j];// multiplicação da matriz pela sua transposta correspondente

            }
        }

I know that in the 1st multiplication of line 1 by the transpose **i0j0*i0j0 + i0j1*i1j0 + i0j2*i2j0** and that in the 2nd multiplication of line 1 by the transpose **i0j0*i0j1 + i0j1*i1j1 + i0j2*i2j1** and that in the 3rd multiplication of line 1 by the transpose **i0j0*i0j2 + i0j1*i1j2 + i0j2*i2j2**

and then in the first multiplication of line 2 by the transpose **i1j0*i0j0 + i1j1*i1j0 + i1j2*i2j0** in the 2nd multiplication of line 2 by the transpose **i1j0*i0j1 + i1j1*i1j1 + i1j2*i2j1** in the 3rd multiplication of line 2 by the transpose **i1j0*i0j2 + i1j1*i1j2 + i1j2*i2j2**

and last in the first multiplication of line 3 by the transpose **i2j0*i0j0 + i2j1*i1j0 + i2j2*i2j0** in the 2nd multiplication of line 3 by the transpose **i2j0*i0j1 + i2j1*i1j1 + i2j2*i2j1** in the 3rd multiplication of line 3 by the transpose **i2j0*i0j2 + i2j1*i1j2 + i2j2*i2j2**

An example, if the array ( mat[i][j] ) entered by the user is 10, 0, 1, 3, 5, 2, -4, 2, 3. The result array ( mat_resultado ) will have the following output numbers: 101, 32, -37, 32, 38, 4, -37, 4, 29.

    
asked by anonymous 10.05.2017 / 14:42

1 answer

2

Firstly the product of two arrays is defined only when the number of columns of the first array is equal to the number of rows of the second array. 

#define L 3
#define M 4
...
    int mat[L][M], mat_transposta[M][L], mat_resultado[L][L];
    int i, j, k;
    ...
    /* Multiplicação*/
    for (i=0; i<L; i++) {
        for (j=0; j<L; j++) {
            mat_resultado[i][j] = 0;
            for (k=0; k<M; k++) {
                mat_resultado[i][j] += mat[i][k] * mat_transposta[k][j];
            }
        }
    }
    ...

In your particular case L and M must have the same value, that is 3.

===================

Consider a matrix product definition to understand the use of the variable k and its loop.

    
10.05.2017 / 15:41
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