GATE 2011 CS (CS1) – Question 48
Matrices M₁,M₂,M₃,M₄ have dimensions p×q,q×r,r×s,s×t. With p=10,q=100,r=20,s=5,t=80, find minimum scalar multiplications.
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Correct answer: (C) 19000
Explanation
Pair costs are 20000,10000,8000. Triple minima are m₁₃=min(10000+5000,20000+1000)=15000 and m₂₄=min(8000+160000,10000+40000)=50000. Final splits cost 130000,44000,19000. The optimum ((M₁(M₂M₃))M₄) costs 10000+5000+4000=19000, C.