Macro economics: Core Commerce Notes for B.Com (Hons)

Macroeconomics – Advanced University‑Level Study Notes

(B.Com (Hons) – Core Commerce – Semester 3/4)

Goal: Build a rigorous, first‑principles understanding of macroeconomic theory.
Audience: B.Com (Hons) students who already know basic accounting and micro‑economics.
Structure:

Foundations – National Income Accounting & the Production‑Possibility Frontier

The Circular‑Flow Model & the Determinants of Aggregate Output

Prices, Inflation & Unemployment – Theory & Empirical Evidence

Macroeconomic Policy – Fiscal, Monetary & Exchange‑Rate Regimes

Advanced Models – IS‑LM, AD‑AS, DSGE & Rational‑Expectations

Edge Cases & Policy Dilemmas

Challenging Problem

Notation:
Y = real GDP, C = consumption, I = investment, G = government spending, NX = net exports, P = price level, π = inflation rate, u = unemployment rate, r = real interest rate, i = nominal interest rate.

1. Foundations

1.1 National Income Accounting

Concept	Formula	Interpretation
Gross Domestic Product (GDP)	( \displaystyle Y = C + I + G + NX )	Total value of final goods/services produced in a country.
Real GDP	( \displaystyle Y_{\text{real}} = \frac{Y_{\text{nominal}}}{P_{\text{deflator}}} )	Adjusted for price changes.
GDP Deflator	( \displaystyle P_{\text{deflator}} = \frac{Y_{\text{nominal}}}{Y_{\text{real}}} )	Broad measure of price level.
National Income (NI)	( \displaystyle NI = Y - T + \text{Transfer} )	Aggregate income after taxes and transfers.
Disposable Income (DI)	( \displaystyle DI = Y - T + \text{Transfer} )	Income available for consumption & savings.
Savings (S)	( \displaystyle S = Y - T - C + \text{Transfer} )	Funds diverted from consumption.
Investment (I)	( \displaystyle I = Y - C - G - NX )	Used in Keynesian identity.

First‑principles justification:
GDP is derived from the expenditure approach (C+I+G+NX) and the income approach (sum of wages, profits, rents). The identity holds because every final expenditure is matched by an income receipt.

1.2 Production‑Possibility Frontier (PPF)

Definition: Set of all feasible combinations of two goods that an economy can produce given its resources and technology.
Mathematical form (two‑good case):
[ f(K, L) = Y_A,\quad g(K, L) = Y_B ]
where (K) = capital, (L) = labor.
Key properties:
1. Downward sloping – trade‑off between goods.
2. Convex to origin – diminishing opportunity cost.
3. Efficiency & Inefficiency – points inside = under‑utilized resources; on the frontier = fully utilized.

Rigorous derivation:
Assume Cobb–Douglas production functions (Y_i = A_i K^{\alpha_i} L^{1-\alpha_i}). Solve for the frontier by holding total capital (K_{\text{tot}}) and labor (L_{\text{tot}}) constant and partitioning them between sectors. The Pareto‑efficient frontier is found by maximizing weighted sum of outputs subject to resource constraints. This yields the isocost line and Lagrangian multiplier interpretation.

2. Circular‑Flow Model & Aggregate Output

2.1 Two‑Sector Circular Flow (Households & Firms)

Households supply labor, demand goods/services.
Firms produce goods, pay wages, distribute profits.

Flow equations:

Flow	Households → Firms	Firms → Households
Money	Consumption C	Wages wL, Profits π
Goods	Labor L, Capital K	Output Y

Equilibrium condition:
[ Y = C + I + G + NX ] and
[ C = c_0 + c_1 (DI) ] where (c_1) is the marginal propensity to consume.

2.2 Determinants of Aggregate Output

Factor	Effect on Y	Intuition
Technology	↑	Increases productivity (A) in production functions.
Capital stock	↑	More capital per worker raises output.
Labor supply	↑	More workers → higher output.
Government spending	↑	Direct injection of demand.
Taxes	↓	Reduce disposable income → lower consumption.
Expectations	↑/↓	Forward‑looking behavior alters investment & consumption.

Rigorous reasoning:
Use the Solow growth model to separate effects of capital accumulation vs. technological progress. The steady‑state condition (sY = (n+δ)K) yields the long‑run output per worker. Technological progress enters via