$\displaystyle u_t = 2u_{xx} \quad $

$\displaystyle T'(t) = -2 \lambda T(t) \quad $

and

$\displaystyle X''(x) = - \lambda X(x). \quad $

Does it make any difference if choose constant to be $\displaystyle \lambda$ and not $\displaystyle -\lambda$ as above

Thanks