The situation is :
There are n bulbs and m power sources. The j-th power source has a failure probability of $P_j$. Each bulb is connected to 3 power sources, and only $\frac{3n}{m}$ bulbs can be connected to one power source. When all the power sources connected to the bulb fail, the bulb fails. How to connect to minimize the expectation of the failure bulb.
Let $x_{ij}$ indicts whether bulbs i connects to power source j. This problem can be modeled as 0-1 integer programming easily:
the constraint is $\sum_{j}x_{ij}=3$ for any i and $\sum_{i}x_{ij}=\frac{3n}{m}$ for and m. Minimize the function $E=\sum_i(1-\prod_j(1-P_j)^{x_{xj}})$
But as the parameters can be pretty large, such as n=1000000 ,m=1000,it may take a lot of time to solve it.
Now suppose $P_i$ has only a few cases, such as $P_i\in\{0.2,0.5,0.7\}$. Considering all variables now having high substitutability, can we simply the model?