虽然说效用只与q有关 但是u（q）的具体形式不知道啊

例如 如果u（q）=1/q,那么就是效用反而和q反比了 反而消费越小效用越大

因此最大效用的消费量不一定是 M/p

The agent maximizes his/her utility under the budget constraint, by choosing the allocation of goods.

q最好写作x，以便作为一个配置。

max u(q) 

subject to p*q=M

where p,M are exogenous.

this linear math problem can be solved , the solution q* is the best allocation.

you'd better use the Lagrange Multiplier to understand the economic implication.

Lagrangian=u(q)+lamda*(M-p*q)

Derive it with repect to q, and you can obtain the first order condition, it means if the agents do the max problem correctly , the optimal allocation must satisfy the FOC.