@@ -25,11 +25,11 @@ formulated an equilibrium model of price and quantity vectors in
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balanced growth, this lecture shows how fruitfully to employ the
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following important tools:
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- - a zero-sum two-player game
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+ - a zero-sum two-player game
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- - linear programming
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+ - linear programming
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- - the Perron-Frobenius theorem
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+ - the Perron-Frobenius theorem
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We'll begin with some imports:
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@@ -353,35 +353,35 @@ Model Ingredients and Assumptions
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A pair :math: `(A,B)` of :math: `m\times n` non-negative matrices defines
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an economy.
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- - :math: `m` is the number of *activities * (or sectors)
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+ - :math: `m` is the number of *activities * (or sectors)
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- - :math: `n` is the number of *goods * (produced and/or consumed).
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+ - :math: `n` is the number of *goods * (produced and/or consumed).
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- - :math: `A` is called the *input matrix *; :math: `a_{i,j}` denotes the
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- amount of good :math: `j` consumed by activity :math: `i`
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+ - :math: `A` is called the *input matrix *; :math: `a_{i,j}` denotes the
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+ amount of good :math: `j` consumed by activity :math: `i`
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- - :math: `B` is called the *output matrix *; :math: `b_{i,j}` represents
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- the amount of good :math: `j` produced by activity :math: `i`
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+ - :math: `B` is called the *output matrix *; :math: `b_{i,j}` represents
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+ the amount of good :math: `j` produced by activity :math: `i`
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Two key assumptions restrict economy :math: `(A,B)`:
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- **Assumption I: ** (every good that is consumed is also produced)
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- .. math :: b_{.,j} > \mathbf{0}\hspace{5mm}\forall j=1,2,\dots,n
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+ .. math :: b_{.,j} > \mathbf{0}\hspace{5mm}\forall j=1,2,\dots,n
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- **Assumption II: ** (no free lunch)
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- .. math :: a_{i,.} > \mathbf{0}\hspace{5mm}\forall i=1,2,\dots,m
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+ .. math :: a_{i,.} > \mathbf{0}\hspace{5mm}\forall i=1,2,\dots,m
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A semi-positive *intensity * :math: `m`-vector :math: `x` denotes levels at which
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activities are operated.
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Therefore,
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- - vector :math: `x^TA` gives the total amount of *goods used in
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- production *
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+ - vector :math: `x^TA` gives the total amount of *goods used in
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+ production *
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- - vector :math: `x^TB` gives *total outputs *
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+ - vector :math: `x^TB` gives *total outputs *
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An economy :math: `(A,B)` is said to be *productive *, if there exists a
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non-negative intensity vector :math: `x \geq 0 ` such
@@ -392,9 +392,9 @@ the :math:`n` goods.
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The :math: `p` vector implies *cost * and *revenue * vectors
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- - the vector :math: `Ap` tells *costs * of the vector of activities
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+ - the vector :math: `Ap` tells *costs * of the vector of activities
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- - the vector :math: `Bp` tells *revenues * from the vector of activities
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+ - the vector :math: `Bp` tells *revenues * from the vector of activities
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Satisfaction or a property of an input-output pair :math: `(A,B)` called *irreducibility *
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(or indecomposability) determines whether an economy can be decomposed
@@ -477,9 +477,9 @@ These timing conventions imply the following feasibility condition:
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.. math ::
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- \begin {aligned}
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- x^T_{t}B \geq x^T_{t+1 } A \hspace {1 cm}\forall t\geq 1
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- \end {aligned}
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+ \begin {aligned}
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+ x^T_{t}B \geq x^T_{t+1 } A \hspace {1 cm}\forall t\geq 1
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+ \end {aligned}
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which asserts that no more goods can be used today than were produced
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yesterday.
@@ -537,10 +537,11 @@ the economy:
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and a number :math: `\alpha\in \mathbb {R}` that satisfy
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.. math ::
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- \begin {aligned}
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- &\max _{\alpha } \hspace {2 mm} \alpha \\
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- &\text {s.t. }\hspace {2 mm}x^T B \geq \alpha x^T A
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- \end {aligned}
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+
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+ \begin {aligned}
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+ &\max _{\alpha } \hspace {2 mm} \alpha \\
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+ &\text {s.t. }\hspace {2 mm}x^T B \geq \alpha x^T A
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+ \end {aligned}
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Theorem 9.3 of David Gale’s book :cite: `gale1989theory ` asserts that if Assumptions I and II are
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both satisfied, then a maximum value of :math: `\alpha ` exists and that it is
@@ -555,10 +556,11 @@ by :math:`\alpha_0`. The associated intensity vector :math:`x_0` is the
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and a number :math: `\beta\in \mathbb {R}` that satisfy
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.. math ::
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- \begin {aligned}
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- &\min _{\beta } \hspace {2 mm} \beta \\
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- &\text {s.t. }\hspace {2 mm}Bp \leq \beta Ap
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- \end {aligned}
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+
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+ \begin {aligned}
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+ &\min _{\beta } \hspace {2 mm} \beta \\
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+ &\text {s.t. }\hspace {2 mm}Bp \leq \beta Ap
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+ \end {aligned}
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Assumptions I and II imply existence of a minimum value
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:math: `\beta _0 >0 ` called the *economic expansion rate *.
@@ -591,11 +593,11 @@ following arbitrage true
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.. math ::
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- \begin {aligned}
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- x_0 ^T B &\geq \gamma ^{* } x_0 ^T A \\
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- Bp_0 &\leq \gamma ^{* } Ap_0 \\
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- x_0 ^T\left (B-\gamma ^{* } A\right )p_0 &= 0
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- \end {aligned}
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+ \begin {aligned}
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+ x_0 ^T B &\geq \gamma ^{* } x_0 ^T A \\
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+ Bp_0 &\leq \gamma ^{* } Ap_0 \\
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+ x_0 ^T\left (B-\gamma ^{* } A\right )p_0 &= 0
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+ \end {aligned}
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..
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@@ -659,18 +661,19 @@ with the entries representing payoffs from the **minimizing** column
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player to the **maximizing ** row player and assume that the players can
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use mixed strategies. Thus,
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- * the row player chooses the :math: `m`-vector :math: `x > \mathbf {0 }` subject to :math: `\iota _m^T x = 1 `
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-
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- * the column player chooses the :math: `n`-vector :math: `p > \mathbf {0 }` subject to :math: `\iota _n^T p = 1 `.
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+ * the row player chooses the :math: `m`-vector :math: `x > \mathbf {0 }` subject to :math: `\iota _m^T x = 1 `
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+
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+ * the column player chooses the :math: `n`-vector :math: `p > \mathbf {0 }` subject to :math: `\iota _n^T p = 1 `.
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**Definition: ** The :math: `m\times n` matrix game :math: `C` has the
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*solution * :math: `(x^*, p^*, V(C))` in mixed strategies if
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.. math ::
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- \begin {aligned}
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- (x^* )^T C e^j \geq V(C)\quad \forall j\in \{ 1 , \dots , n\}\quad \quad
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- \text {and}\quad\quad (e^i)^T C p^* \leq V(C)\quad \forall i\in \{ 1 , \dots , m\}
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- \end {aligned}
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+
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+ \begin {aligned}
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+ (x^* )^T C e^j \geq V(C)\quad \forall j\in \{ 1 , \dots , n\}\quad \quad
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+ \text {and}\quad\quad (e^i)^T C p^* \leq V(C)\quad \forall i\in \{ 1 , \dots , m\}
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+ \end {aligned}
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The number :math: `V(C)` is called the *value * of the game.
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@@ -693,7 +696,8 @@ zero-sum game.
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Moreover, von Neumann’s Minmax Theorem :cite: `neumann1928theorie ` implies that
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.. math ::
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- V(C) = \max _x \min _p \hspace {2 mm} x^T C p = \min _p \max _x \hspace {2 mm} x^T C p = (x^*)^T C p^*
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+
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+ V(C) = \max _x \min _p \hspace {2 mm} x^T C p = \min _p \max _x \hspace {2 mm} x^T C p = (x^*)^T C p^*
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@@ -703,33 +707,35 @@ Connection with Linear Programming (LP)
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Nash equilibria of a finite two-player zero-sum game solve a linear programming problem.
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To see this, we introduce
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- the following notation
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-
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- * For a fixed :math: `x`, let :math: `v` be the value of the minimization problem: :math: `v \equiv \min _p x^T C p = \min _j x^T C e^j`
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-
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- * For a fixed :math: `p`, let :math: `u` be the value of the maximization problem: :math: `u \equiv \max _x x^T C p = \max _i (e^i)^T C p`
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+ the following notation
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+
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+ * For a fixed :math: `x`, let :math: `v` be the value of the minimization problem: :math: `v \equiv \min _p x^T C p = \min _j x^T C e^j`
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+
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+ * For a fixed :math: `p`, let :math: `u` be the value of the maximization problem: :math: `u \equiv \max _x x^T C p = \max _i (e^i)^T C p`
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Then the *max-min problem * (the game from the maximizing player’s point
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of view) can be written as the *primal * LP
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.. math ::
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- \begin {aligned}
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- V(C) = & \max \hspace {2 mm} v \\
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- \text {s.t. } \hspace {2 mm} v \iota _n^T &\leq x^T C \\
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- x &\geq \mathbf {0 } \\
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- \iota _n^T x & = 1
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- \end {aligned}
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+
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+ \begin {aligned}
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+ V(C) = & \max \hspace {2 mm} v \\
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+ \text {s.t. } \hspace {2 mm} v \iota _n^T &\leq x^T C \\
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+ x &\geq \mathbf {0 } \\
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+ \iota _n^T x & = 1
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+ \end {aligned}
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while the *min-max problem * (the game from the minimizing player’s point
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of view) is the *dual * LP
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.. math ::
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- \begin {aligned}
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- V(C) = &\min \hspace {2 mm} u \\
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- \text {s.t. } \hspace {2 mm}u \iota _m &\geq Cp \\
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- p &\geq \mathbf {0 } \\
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- \iota _m^T p & = 1
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- \end {aligned}
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+
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+ \begin {aligned}
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+ V(C) = &\min \hspace {2 mm} u \\
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+ \text {s.t. } \hspace {2 mm}u \iota _m &\geq Cp \\
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+ p &\geq \mathbf {0 } \\
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+ \iota _m^T p & = 1
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+ \end {aligned}
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Hamburger, Thompson and Weil :cite: `hamburger1967computation ` view the input-output pair of the
@@ -761,21 +767,22 @@ zero-sum game, we define a matrix for :math:`\gamma\in\mathbb{R}`
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For fixed :math: `\gamma `, treating :math: `M(\gamma )` as a matrix game,
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calculating the solution of the game implies
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- - If :math: `\gamma > \alpha _0 `, then for all :math: `x>0 `, there
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- :math: `\exists j\in \{ 1 , \dots , n\}`, s.t.
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- :math: `[x^T M(\gamma )]_j < 0 ` implying
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- that :math: `V(M(\gamma )) < 0 `.
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- - If :math: `\gamma < \beta _0 `, then for all :math: `p>0 `, there
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- :math: `\exists i\in \{ 1 , \dots , m\}`, s.t.
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- :math: `[M(\gamma )p]_i > 0 ` implying that :math: `V(M(\gamma )) > 0 `.
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- - If :math: `\gamma \in \{\beta _0 , \alpha _0 \}`, then (by Theorem I) the
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- optimal intensity and price vectors :math: `x_0 ` and :math: `p_0 `
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- satisfy
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+ - If :math: `\gamma > \alpha _0 `, then for all :math: `x>0 `, there
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+ :math: `\exists j\in \{ 1 , \dots , n\}`, s.t.
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+ :math: `[x^T M(\gamma )]_j < 0 ` implying
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+ that :math: `V(M(\gamma )) < 0 `.
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+ - If :math: `\gamma < \beta _0 `, then for all :math: `p>0 `, there
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+ :math: `\exists i\in \{ 1 , \dots , m\}`, s.t.
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+ :math: `[M(\gamma )p]_i > 0 ` implying that :math: `V(M(\gamma )) > 0 `.
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+ - If :math: `\gamma \in \{\beta _0 , \alpha _0 \}`, then (by Theorem I) the
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+ optimal intensity and price vectors :math: `x_0 ` and :math: `p_0 `
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+ satisfy
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.. math ::
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- \begin {aligned}
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- x_0 ^T M(\gamma ) \geq \mathbf {0 }^T \quad \quad \text {and}\quad\quad M(\gamma ) p_0 \leq \mathbf {0 }
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- \end {aligned}
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+
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+ \begin {aligned}
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+ x_0 ^T M(\gamma ) \geq \mathbf {0 }^T \quad \quad \text {and}\quad\quad M(\gamma ) p_0 \leq \mathbf {0 }
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+ \end {aligned}
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That is, :math: `(x_0 , p_0 , 0 )` is a solution of the game
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:math: `M(\gamma )` so
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Compute :math: `\alpha _0 ` and :math: `\beta _0 `
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- - Finding :math: `\alpha _0 `
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-
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- 1. Fix :math: `\gamma = \frac {UB + LB}{2 }` and compute the solution
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- of the two-player zero-sum game associated
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- with :math: `M(\gamma )`. We can use either the primal or the dual
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- LP problem.
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- 2. If :math: `V(M(\gamma )) \geq 0 `, then set :math: `LB = \gamma `,
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- otherwise let :math: `UB = \gamma `.
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- 3. Iterate on 1. and 2. until :math: `|UB - LB| < \epsilon `.
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+ - Finding :math: `\alpha _0 `
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- - Finding :math: `\beta _0 `
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+ 1. Fix :math: `\gamma = \frac {UB + LB}{2 }` and compute the solution
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+ of the two-player zero-sum game associated
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+ with :math: `M(\gamma )`. We can use either the primal or the dual
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+ LP problem.
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+ 2. If :math: `V(M(\gamma )) \geq 0 `, then set :math: `LB = \gamma `,
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+ otherwise let :math: `UB = \gamma `.
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+ 3. Iterate on 1. and 2. until :math: `|UB - LB| < \epsilon `.
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- 1. Fix :math: `\gamma = \frac {UB + LB}{2 }` and compute the solution
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- of the two-player zero-sum game associated.
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- with :math: `M(\gamma )`. We can use either the primal or the dual
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- LP problem.
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- 2. If :math: `V(M(\gamma )) > 0 `, then set :math: `LB = \gamma `,
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- otherwise let :math: `UB = \gamma `.
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- 3. Iterate on 1. and 2. until :math: `|UB - LB| < \epsilon `.
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+ - Finding :math: `\beta _0 `
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+ 1. Fix :math: `\gamma = \frac {UB + LB}{2 }` and compute the solution
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+ of the two-player zero-sum game associated.
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+ with :math: `M(\gamma )`. We can use either the primal or the dual
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+ LP problem.
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+ 2. If :math: `V(M(\gamma )) > 0 `, then set :math: `LB = \gamma `,
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+ otherwise let :math: `UB = \gamma `.
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+ 3. Iterate on 1. and 2. until :math: `|UB - LB| < \epsilon `.
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- *Existence *: Since :math: `V(M(LB))>0 ` and :math: `V(M(UB))<0 ` and
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- :math: `V(M(\cdot ))` is a continuous, nonincreasing function, there is
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- at least one :math: `\gamma\in [LB, UB]`, s.t. :math: `V(M(\gamma ))=0 `.
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+ *Existence *: Since :math: `V(M(LB))>0 ` and :math: `V(M(UB))<0 ` and
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+ :math: `V(M(\cdot ))` is a continuous, nonincreasing function, there is
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+ at least one :math: `\gamma\in [LB, UB]`, s.t. :math: `V(M(\gamma ))=0 `.
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The *zerosum * method calculates the value and optimal strategies
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associated with a given :math: `\gamma `.
@@ -997,11 +1003,11 @@ for non-negative matrices.
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**Definition: ** We call an economy *simple * if it satisfies
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- * :math: `n=m`
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-
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- * Each activity produces exactly one good
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+ * :math: `n=m`
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+
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+ * Each activity produces exactly one good
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- * Each good is produced by one and only one activity.
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+ * Each good is produced by one and only one activity.
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These assumptions imply that :math: `B=I_n`, i.e., that :math: `B` can be
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written as an identity matrix (possibly after reshuffling its rows and
@@ -1011,8 +1017,9 @@ The simple model has the following special property (Theorem 9.11. in Gale :cite
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with :math: `(A,I_n)`, then
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.. math ::
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- x_0 ^T = \alpha _0 x_0 ^T A\hspace {1 cm}\Leftrightarrow \hspace {1 cm}x_0 ^T
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- A=\left (\frac {1 }{\alpha _0 }\right )x_0 ^T
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+
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+ x_0 ^T = \alpha _0 x_0 ^T A\hspace {1 cm}\Leftrightarrow \hspace {1 cm}x_0 ^T
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+ A=\left (\frac {1 }{\alpha _0 }\right )x_0 ^T
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The latter shows that :math: `1 /\alpha _0 ` is a positive eigenvalue of
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:math: `A` and :math: `x_0 ` is the corresponding non-negative left
@@ -1032,4 +1039,5 @@ Suppose that :math:`A` is reducible with :math:`k` irreducible subsets
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associated expansion and interest factors, respectively. Then we have
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.. math ::
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- \alpha _0 = \max _i \{\alpha _i\}\hspace {1 cm}\text {and}\hspace {1 cm}\beta _0 = \min _i \{\beta _i\}
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+
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+ \alpha _0 = \max _i \{\alpha _i\}\hspace {1 cm}\text {and}\hspace {1 cm}\beta _0 = \min _i \{\beta _i\}
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