'Latex Printing method.'

def _latex(self, printer=None):

    from sympy.physics.vector.printing import VectorLatexPrinter
    ar = self.args
    if (len(ar) == 0):
        return str(0)
    ol = []
    for (i, v) in enumerate(ar):
        for j in (0, 1, 2):
            if (ar[i][0][j] == 1):
                ol.append(('    +    ' + ar[i][1].latex_vecs[j]))
            elif (ar[i][0][j] == (-1)):
                ol.append(('    -    ' + ar[i][1].latex_vecs[j]))
            elif (ar[i][0][j] != 0):
                arg_str = VectorLatexPrinter().doprint(ar[i][0][j])
                if isinstance(ar[i][0][j], Add):
                    arg_str = ('(%s)' % arg_str)
                if (arg_str[0] == '-'):
                    arg_str = arg_str[1:]
                    str_start = '    -    '
                else:
                    str_start = '    +    '
                ol.append(((str_start + arg_str) + ar[i][1].latex_vecs[j]))
    outstr = ''.join(ol)
    if outstr.startswith('    +    '):
        outstr = outstr[3:]
    elif outstr.startswith('    '):
        outstr = outstr[1:]
    return outstr
