How do you convert this summation to dot notation?

[Atrox]

$$\sum_{\ell=1}^{u-1} b_{u+1}$$

 

[Harry_the_cat]

For this to make sense, there should be an $\ell$ in the expression after the sigma sign.

 

[Atrox]

For this to make sense, there should be an $\ell$ in the expression after the sigma sign.

so you are saying that it is totally incorrect notation?

 

[Dr.Peterson]

so you are saying that it is totally incorrect notation?

It isn't totally incorrect, but it surely doesn't mean what you intend! The value of the sum is just $(u-1)b_{u+1}$, because you are adding up $u-1$ copies of the constant $b_{u+1}$.

There's also the question of what "dot notation" means! Perhaps you mean expanding the summation into an explicit sum, which as written would be $\underset{u-1}{\underbrace{b_{u+1}+b_{u+1}+\dots+b_{u+1}}}$.