Matrix Multiplication

It always frightens us when we hear the word “Matrix” and the complex computations involved in Multiplying two Prime Numbers.

Lets take a look at the serial code , Brute force approach

Brute force

Brute Force Serial

  • Input: matrices A and B
  • Let C be a new matrix of the appropriate size
  • Pick a tile size T = Θ(√M)
  • For I from 1 to n in steps of T:
    • For J from 1 to p in steps of T:
      • For K from 1 to m in steps of T:
        • Multiply AI:I+T, K:K+T and BK:K+T, J:J+T into CI:I+T, J:J+T, that is:
        • For i from I to min(I + T, n):
          • For j from J to min(J + T, p):
            • Let sum = 0
            • For k from K to min(K + T, m):
              • Set sum ← sum + Aik × Bkj
            • Set CijCij + sum
  • Return C

Is the Algorithm for Brute force is optimal for smaller sizes

Divide and Conquer 
Divide and Conquer Serial

  • Inputs: matrices A of size n × m, B of size m × p.
  • Base case: if max(n, m, p) is below some threshold, use an unrolled version of t
  • If max(n, m, p) = n, split A horizontally:

Now Serial Divide and Conquer- D & C (Serial)


Now Strassen Matrix Multiplication Strassen Serial


Source : WIKIPEDIA for algo


Author: Chandher Shekar

Studying Computer Science in PES University.

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