Gate 1994
Duration: 2 min
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The video features an educational lecture on graph theory, specifically analyzing counting problems from GATE examinations. The instructor solves two distinct questions: one involving the summation of graphs with up to three nodes, and another deriving the general formula for the number of undirected graphs on n vertices. The lesson emphasizes the relationship between the number of vertices, possible edges, and the total number of distinct simple graphs.
Chapters
0:00 – 2:00 00:00-02:00
The instructor tackles a GATE-1994 question asking for the number of distinct simple graphs with up to three nodes. He underlines 'up to three nodes' to highlight that the answer requires summing the counts for 1, 2, and 3 vertices. He writes |V|=1, |V|=2, and |V|=3 on the screen. He introduces the formula for the number of possible edges, n(n-1)/2, and the total number of graphs, 2^(n(n-1)/2). He calculates the specific counts: 1 graph for 1 node (2^0), 2 graphs for 2 nodes (2^1), and 8 graphs for 3 nodes (2^3). Although he briefly circles option (c) 8, he proceeds to sum these (1+2+8) to arrive at the total of 11, identifying the correct option.
2:00 – 2:18 02:00-02:18
The lecture shifts to a GATE-2001 question asking for the number of undirected graphs constructible from a set of n vertices. The instructor underlines 'undirected graphs' and 'not necessarily connected' to define the problem constraints. He circles option (D), 2^(n(n-1)/2). He explains that for n vertices, the number of possible edges is n(n-1)/2. Since each edge has two states (present or absent), the total number of graphs is 2 raised to the power of the number of edges. He writes |V|=n and derives the edge count formula to justify the final answer, confirming the exponential relationship.
The lesson progresses from a specific numerical example to a general theoretical formula. The instructor first demonstrates the calculation for small n to build intuition, showing that 'up to n' implies a summation of cases. Then, he generalizes this to finding the total number of graphs for a fixed n, reinforcing the exponential relationship based on the number of possible edges. This progression helps students understand both the calculation method and the underlying combinatorial logic required for such problems.