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  3. Linear Algebra Foundations
  4. Linear Algebra Foundations #4- Matrix Multiplication
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Linear Algebra Foundations #4- Matrix Multiplication

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10 Discussions

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  • jachi334
     + 0 comments
    A = [[1,2,3],[2,3,4],[1,1,1]]
B = [[4,5,6],[7,8,9],[4,5,7]]

ROWS_A, COLS_A = len(A), len(A[0])
ROWS_B, COLS_B = len(B), len(B[0])
assert COLS_A == ROWS_B
COMMON_D = ROWS_B

# zeros for Rows-A x Cols-B
M_TIMES = []
for r in range(ROWS_A):
    M_TIMES.append( [0] * COLS_B )

# Loop over Rows-A, then Cols-B, then the common dimension
for rA in range(ROWS_A):
    for cB in range(COLS_B):
        for t in range(COMMON_D):
            M_TIMES[rA][cB] += A[rA][t]*B[t][cB]
        print(M_TIMES[rA][cB])

  • 22it157
     + 0 comments

    include

    include

    include

    using namespace std; int minCostMatrixMultiplication(vector& dimensions) { int n = dimensions.size() - 1; vector> dp(n, vector(n, 0)); for (int len = 1; len < n; len++) { for (int i = 0; i < n - len; i++) { int j = i + len; dp[i][j] = INT_MAX; for (int k = i; k < j; k++) { int cost = dp[i][k] + dp[k + 1][j] + dimensions[i] * dimensions[k + 1] * dimensions[j + 1]; dp[i][j] = min(dp[i][j], cost); } } } return dp[0][n - 1]; } int main() { int n; cin >> n; vector dimensions(n + 1); for (int i = 0; i <= n; i++) { cin >> dimensions[i]; } int result = minCostMatrixMultiplication(dimensions); cout< 

    return 0;

    }

  • cafelatte
     + 0 comments

    Boring as hell ...

    Python3 

    mmul = lambda m1, m2: [[sum(aij*bjk for aij, bjk in zip(ai, bk))
                        for bk in zip(*m2)] for ai in m1]

a = [[1,2,3],[2,3,4],[1,1,1]]
b = [[4,5,6],[7,8,9],[4,5,7]]

for row in mmul(a, b):
    for i in row: print(i)

  • hoangziet22
     + 0 comments
    a = [1, 2,3], [2, 3,4],[1,1,1]
b = [4, 5,6], [7, 8,9],[4,5,7]
res = 0 
for i in range(3):
    for j in range(3):
            for k in range(3):
                    res += a[i][k]*b[k][j]           
            print(res)
            res = 0

  • chisom213
     + 0 comments
    if __name__ == "__main__":
    M = [[1, 2, 3], [2, 3, 4], [1, 1, 1]]
    N = [[4, 5, 6], [7, 8, 9], [4, 5, 7]]  
    P = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
    
    for i in range(len(M)):
        for j in range(len(N[0])):
            for k in range(len(N)):
                P[i][j] += M[i][k] * N[k][j]
    for j in P:
        print(*j, sep='\n')

    or

    if __name__ == "__main__":
    M = [[1, 2, 3], [2, 3, 4], [1, 1, 1]]
    N = [[4, 5, 6], [7, 8, 9], [4, 5, 7]]
    
    lst = []
    for row in M:
        for i in range(len(row)-2):
            lst += [row[i]*N[0][0] + row[i+1]*N[1][0] + row[i+2]*N[2][0]]
            lst += [row[i]*N[0][1] + row[i+1]*N[1][1] + row[i+2]*N[2][1]]
            lst += [row[i]*N[0][2] + row[i+1]*N[1][2] + row[i+2]*N[2][2]]
    print(*lst, sep='\n')