I have a homework with the problem set like the following:
When a B-spline is evaluated at one of its knots it can be simplified according to the formula
$B(t_i | t_j,...,t_{j+1+p}) = B(t_i | t_j,...,t_{i-1},t_{i+1},t_{j+1+p})$
What does the vertical bar means here? I can see that the right hand side skips $t_i$.
My guess ...
The vertical bar just serves to separate the function argument from other numbers that are used in the function's definition.
So, $B(t | t_r, \ldots , t_s)$ denotes the value at $t$ of the b-spline that is constructed from the knots $t_r, \ldots , t_s$.