Budget Constraintu
Describe budget constraint–
Algebra :

B(p1, … , pn, m) ={ (x1, … , xn) | x1
³ 0, … , xn
³ 0 and p1x1
+ … + pnxn
£ m }

–
Graph： u
Describe changes in budget constraintu
Government programs and budget constraintsu
Non-linear budget lines上图是基本的，税收和补贴、Quantity Discount，Quantity Penalty，One Price Negative The Food Stamp Program，Uniform Ad
Valorem Sales Taxes，都可以看做商品价格或收入发生变动，从而预算线斜率，截距发生变动。



3. Preferences

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Describe preferences：strict preference;
indifference;
weak preference
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三大公理：完备性，反身性，传递性l
Indifference curves (
无差异曲线)无差异曲线形状很多：良好性状的、完全互补、完全替代等。
l
Well-behaved preferences：
Monotonicity（单调性）: More of any commodity is always preferred (i.e. no satiation and every commodity is a good).
Convexity (凸性): Mixtures of bundles are (at least weakly) preferred to the bundles themselves.

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Marginal rate of substitution (
边际替代率)MRS= dx2/dx1，大概讲就是为放弃一单位x1，需要多少单位x2补偿以保持相同效用。
4. Utilityu
Utility function (效用函数）–
Definition–
Monotonic transformation （单调转换）效用函数能够进行单调转化本身表明我们使用的是序数效用论。单调转换的特性在解题中能起到简化的作用。
常见的效用函数有：V(x1,x2) = x1 + x2.，W(x1,x2) = min{x1,x2}.，U(x1,x2) = f(x1) + x2 ，U(x1,x2) = x1a x2b

拟线性偏好在科斯定理那里有重要运用。
u
Marginal rate of substitution 边际替代率 这个式子推导：U(x1,x2) º k，全微分：

既然单调变换后表示的是同一组无差异曲线，当然MRS不变