def matrix(rows,columns,val):
    """
    Bulds a matrix of size rows x columns, with val values in cells

    NOTE: Does not checks negative values
    Parameters
    ----------
    rows(int) : The number of rows of the matrix
    columns(int) : The number of columns of the matrix
    val(int) : The value in every cell of the matrix

    Returns
    -------
    list : The matrix
    """
    matrix = []
    for i in range(rows):
        row = []
        for j in range(columns):
            column = val
            row += [column]
        matrix += [row]
    return matrix