calculating b splines with non-distinct knots How can one calculate B splines with non distinct knots. I know about carl de boor algorithm, but that is to my knowledge only applied to non distinct knots. We can assume the knots are in increasing order. In particular im looking to find $B_0^4(x)$ with knots being $x_0 = 0 \ x_1 = 0 \ x_2 = 1 \ x_3 = 2 \ x_4 = 2$ But how do you do it generally?

Just use deBoor's algorithm. It doesn't require distinct knots.

However ...
I assume that $B_0^4(x)$ means the b-spline basis function of order four (degree three) that is non-zero over the interval between knots $t_0$ and $t_4$. If my assumption is correct, you're in trouble. A basis function of order $4$ depends on six knots, and you have only five knots.