Multiplication of matrix in C

I have a problem with this program, I need in an array [4] [4] to find the maximum of each line and multiply by each line number, in my program it has a syntax error, because I keep the largest number and it only multiplies by the last number of each line for example:

mat[i][j]={0, 1, 2, 3,
           4, 5, 6, 7,
           8, 9, 10, 11,
           12, 13, 14, 15}

would be:

 mat[i][j]={0, 1, 2, 9,
            4, 5, 6, 49,
            8, 9, 10, 121,
            12, 13, 14, 225}

My code:

#include <stdio.h>
#include <stdlib.h>
#include <locale.h>

//achar maior menor de cada linha da matriz
int main(int argc, char *argv[]) 
{
    int mat[4][4];
    int i, j, aux;

    //le matriz
    for(i=0; i<=3; i++)
    {
        for(j=0; j<=3; j++)
        {
            setlocale(LC_ALL, "Portuguese");
            printf("digite um numero para a posição %d e coluna %d de mat:\n", i, j);
            scanf("%d", &mat[i][j]);
        }
    }

    //1ºfase de processamento
    for(i=0; i<=3; i++)
{
    for(j=0; j<=3; j++)
    {
        if(mat[i][j]>=mat[i][j])//se o elemento na posição mat={i,j} 
                                //for maior que o ultimo elemento da linha
        {
            aux=mat[i][j];//guardar em aux
            mat[i][j]=mat[i][j]*aux;
        }
    }
}

If someone knows what I did wrong, I would like some explanation I'm having a lot of syntax problem.