probability wheel, redistribution of probabilities I have a contiguous ordered data structure (0 based index): 

x= [1/3, 1/3, 1/3]


Let's say I selected index 1 and increased the probability by 1/3. Rest of the probabilities each decrease by 1/6 and the total probability remains P = 1.

x= [1/6, 2/3, 1/6]


Let's say I selected index 2 and increased the probability by 1/3. Rest of the probabilities in total need to decrease by 1/3 to make the total probability remain P= 1.

x= [1/10, 2/5, 1/2]


Is there a name for this kind of data structure? I'd like to research that name and use a library instead of my custom rolled code if possible.
This can be easily achieved by an  array $A$ and an additional variable $m$. The entry $A[i]$ stores the probability of $i$ times $m$.

In your example you start with

A=[1,1,1], m=3


The you increase the probability of the second element by 1/3. This can be carried out by setting $A[2]=4$ and $m=6$, which gives

A=[1,4,1], m=6


In general you could set the probability of element $k$ to $p$ by solving the system
$$\sum_i A[i] = m \text{ and } A[k]=p\cdot m,$$
for the unknowns $A[k]$ and $m$.

So all you need to do is to set $m$ to 
$$ m = \frac{\sum_{i\neq k} A[i]}{1-p},$$
and $A[k]=p\cdot m$ for the new $m$.