naive implementation and optimized solution in c program of the above that does computation no less than 2n^3.

We consider a special case of matmul where A, B, and C are n x n matrices. This can be performed using 2n floating point operations (n' adds n multiplies), as in the following pseudocode: for i = 1 to n for j = 1 to n for k-1 ton end end end