I have two vectors $\bf a$ and $\bf b$. Each time I use a fixed value for $\bf a$ (i.e. not a vector) and a vector $\bf b$ or a vector $\bf a$ and fix value for $\bf b$ (i.e. not a vector).
The equation has the following form:
\begin{equation} W(a,b)= W_0(ke^{- {\bf a}r_1-{\bf b}r_2}+ (1-k)e^{- {\bf a}r_3-{\bf b}r_4}) \end{equation}
where $k ,r_1, r_2, r_3, r_4$ are constants.
My question is the following. Is the above notation correct or should I have to write the above equation like this? \begin{equation} W({\bf a},{\bf b})= W_0(ke^{- {\bf a}r_1-{\bf b}r_2}+ (1-k)e^{- {\bf a}r_3-{\bf b}r_4}) \end{equation}