Matrix Multiplication: Calculating (AB)C and A(BC) Using the Formula

We get ((AB)C)_{ij}=\sum_k\sum_pA_{ip}B_{pk}C_{kj}. Similarly, for (A(BC)), we get (A(BC))_{ij}=\sum_pA_{ip}(BC)_{pj}=\sum_k\sum_pA_{ip}B_{pk}C_{kj}. In summary, to calculate ((AB)C) and (A(BC)), we use the formula (AB)ij = Pk AikBkj twice, first on (AB) and then on (A(BC)).
  • #1
P-Jay1
32
0
A is an M × N matrix, B is N × K and C is a K × L matrix. Consider matrix
multiplication (AB)ij = Pk AikBkj .

Using the formula, (AB)ij = Pk AikBkj, how would I calculate ((AB)C) and (A(BC))?
 
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  • #2
P-Jay1 said:
A is an M × N matrix, B is N × K and C is a K × L matrix. Consider matrix
multiplication (AB)ij = Pk AikBkj .

Using the formula, (AB)ij = Pk AikBkj, how would I calculate ((AB)C) and (A(BC))?
Just use the formula twice (on each of those products). Start with [tex]((AB)C)_{ij}=\sum_k(AB)_{ik}C_{kj}.[/tex] Now use the formula again to evaluate [itex](AB)_{ik}[/itex].
 

What is matrix multiplication?

Matrix multiplication is a mathematical operation where two matrices are multiplied together to produce a new matrix. It is different from regular multiplication as it follows a specific set of rules and involves multiplying every element of one matrix with every element of the other matrix.

How is matrix multiplication performed?

Matrix multiplication involves multiplying the rows of the first matrix with the columns of the second matrix and adding the products. The result is a new matrix with the number of rows from the first matrix and the number of columns from the second matrix. This operation can only be performed if the number of columns in the first matrix is equal to the number of rows in the second matrix.

What are the rules for matrix multiplication?

The rules for matrix multiplication are:

  1. The number of columns in the first matrix must be equal to the number of rows in the second matrix.
  2. The resulting matrix will have the same number of rows as the first matrix and the same number of columns as the second matrix.
  3. The order of multiplication matters, AB is not equal to BA.
  4. The elements in the resulting matrix are found by multiplying the corresponding elements in each row of the first matrix with each column of the second matrix and adding the products.

Why is matrix multiplication important?

Matrix multiplication is an important operation in linear algebra as it allows for the representation and manipulation of linear equations and systems. It is also used in many fields such as computer graphics, physics, and economics, to name a few.

What is the difference between matrix multiplication and scalar multiplication?

Matrix multiplication involves multiplying two matrices together, while scalar multiplication involves multiplying a single matrix by a constant number. Matrix multiplication follows a specific set of rules, while scalar multiplication is simply multiplying every element of the matrix by the scalar value. Additionally, the result of matrix multiplication is a new matrix, while the result of scalar multiplication is still the same size matrix as the original matrix.

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