Even if it may appear from the equation that Bvector updates are independent of each other, in reality, they are repeating the same calculations again and again.
The values in the matrix Matrixx are never updated inside the t loop. You can reuse the multiplications done on Matrixx for all B(i,j,k) calculations, using dynamic programming.
Basically, B(i,j,k) is made up of same Matrixx values as that of B(i,j,k - 1), with few addititons. This can be written as,
I might be slightly off on the equation, but the idea remains the same. Try to reuse as much computed values as possible.
The t loop can't be parallelized, as it depends on previous iteration of the loop. There might be other optimization opportunities, such as reducing cache misses, removing any branching that may exists, etc.