P13BEF-E1 ADVANCED CALCULUS FOR BUSINESS, ECONOMICS AND FINANCE 2018-2019
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
P13BEF-E1
A LEVEL 3 MODULE, AUTUMN SEMESTER 2018-2019
ADVANCED CALCULUS FOR BUSINESS, ECONOMICS AND FINANCE
1. (a) Circle the words in the brackets that correctly complete the following sentence:
Suppose a 3 by 5 matrix A has rank r =3. Then the equation Ax = b (always / sometimes but not
always) has (a unique solution / many solutions / no solution).
(b) Find determinant of matrix A without carrying out any computation and give a reason.
A = [ ]
(c) Compute the inverse of the following matrix.
[ ]
2. In an economic model the endogenous variables x1, x2, … , xn are related to the exogenous variables b1 , b2, … , bn by the linear system
a21 x1 + a22x2 + ⋯ + a2nxn = b2
⋮ ⋮
an1x1 + an2x2 + ⋯ + ann xn = bn
, or in matrix form Ax = b.
Assume that the n × n matrix A has an inverse. For each choice of b the vector x is uniquely determined by x = A −1 b. Suppose bj changes to bj + 6j , but all the other bi’s are unchanged.
The corresponding values of the endogenous variables will then (in general) all changed. Let the change in xi be denoted by Δxi .
Show that Δxi = , where Cji is the (i,j)th element of the adjoint matrix of A.
(Hint: apply Cramer’s rule)
3. (a) Suppose Y = Y(t) is national product, C(t) is consumption at time t , and I is fixed investment. Suppose Ẏ = a(C + I − Y) and C = FY + C0 , with a > 0 and F > 0 . Derive a differential equation for Ẏ as a function of Y and the constants. (5 Marks)
(b) Find its solution when Y(0) = Y0 . When is the equation stable (that is to have Y(t) being finite
when t → ∞)? What is Y(t) as t → ∞ in the stable case?
4. (a) In a market the supply function is S(p) = −1 + 16p, and the demand at time t is D(p, t) = 20e−2t + 59 − 4p. Suppose the instantaneous rate of change of the price, ṗ(t) is 10% of the excess demand D(p, t) − S(p). At time t = 0, p(0) = 6.
(i) Formulate a differential equation for the price development.
(ii) Solve the equation in (i). What is the limit of the price as t → ∞?
(b) Solve the differential equation 2 + 4Ẋ − 30X = 3t2 − 2
5. Solve the control problem
maX ∫ (X − u2 )dt,
Ẋ = u, X (0) = 1, X (1) fTee, u ∈ (−∞, ∞)
2022-08-02