Math Problem Statement

Find a solution to the following divide-and-conquer recurrence relations. You may use any method.

For all problems, assume that T(1) = 1.

(1) (Home Work) T(n) = 3T(n/2) + n lg n.

T(1) = 1, T(n) = 3T(n/2) + n log n

let n = 2^k, k = 0,1,2,3,...,infinity

T(2^k) = 3T((2^K)/2) + 2^K (log{2^k})

= 3T(2^{k-1}) + 2k^2 (k) (log{2})

= 3T(2^{k-1}) + k2^k

3T(2^k) - T(2^{k-1}) = k2^k

(x-1)(x-2) = 0

r_1 = 1, r_2 =2

general solution: T(2^k) = c_1 + A(2^k)

finding constants from boundary conditions

k = 0 => T(2^0) = T(1) = 1

k = 1 => T(2^1) = 3T(1) + 2 (log(2)) = 5

k = 0 => c_1 + A(2^0) = 1

k = 1 => c_1 + A(2^1) = 5

solving for the constants c_1 = -3, A = 4

T(2^k) = -3 + 4(2^k)

since n=2^k => k = log_2{n}

T(n) = -3+4(2^{log_2 n})

is it correct? if not then correct it

Solution

The initial approach has a few issues, so let's work through the problem carefully to verify and correct it.

Given: T(n)=3T(n2)+nlognT(n) = 3T\left(\frac{n}{2}\right) + n \log n with T(1)=1T(1) = 1.

We will use the recurrence relation and the Master Theorem to solve this.

Step 1: Verify Applicability of the Master Theorem

For the recurrence relation T(n)=aT(nb)+f(n)T(n) = a \, T\left(\frac{n}{b}\right) + f(n), we have:

  • a=3a = 3,
  • b=2b = 2, and
  • f(n)=nlognf(n) = n \log n.
  1. Calculate nlogban^{\log_b a}: logba=log23.\log_b a = \log_2 3. Thus, nlogba=nlog23n1.585n^{\log_b a} = n^{\log_2 3} \approx n^{1.585}.

  2. Compare f(n)=nlognf(n) = n \log n with nlogban^{\log_b a}:

    • nlognn \log n grows more slowly than nlog23n^{\log_2 3} because log23>1\log_2 3 > 1.
    • Therefore, f(n)=O(nlog23ϵ)f(n) = O(n^{\log_2 3 - \epsilon}) for some ϵ>0\epsilon > 0.

Since f(n)f(n) grows more slowly than nlogban^{\log_b a}, by the Master Theorem, the solution to this recurrence relation is: T(n)=Θ(nlog23).T(n) = \Theta(n^{\log_2 3}).

Final Answer

T(n)=Θ(nlog23),T(n) = \Theta(n^{\log_2 3}), where nlog23n1.585n^{\log_2 3} \approx n^{1.585}.

This is the asymptotic solution to the recurrence relation.


Would you like a detailed breakdown of each calculation or have further questions?

Related Problems

  1. Solve the recurrence T(n)=2T(n/2)+nT(n) = 2T(n/2) + n.
  2. Find the solution for T(n)=4T(n/2)+n2T(n) = 4T(n/2) + n^2.
  3. Solve T(n)=T(n/2)+nlognT(n) = T(n/2) + n \log n using the Master Theorem.
  4. Determine the solution to T(n)=3T(n/3)+nT(n) = 3T(n/3) + n.
  5. Use the recursion tree method to solve T(n)=3T(n/4)+nT(n) = 3T(n/4) + n.

Tip

For divide-and-conquer recurrences, start by identifying aa, bb, and f(n)f(n) terms to quickly assess whether the Master Theorem applies.

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Math Problem Analysis

Mathematical Concepts

Recurrence Relations
Divide and Conquer
Asymptotic Analysis

Formulas

Master Theorem
T(n) = aT(n/b) + f(n)

Theorems

Master Theorem

Suitable Grade Level

Grades 11-12