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def multM(a, b): '''essa foi a função que eu tentei fazer'''
if len(a) == len(b[0]):
r = []
for i in range(len(a)):
r.append([])
for j in range(len(b[0])):
for k in range(len(a)):
val = a[i][j] * b[k][i]
r[-1].append(val)
return r
2
You can do two functions:
getLinha(matriz, n) returns a list of line values n.
getColuna(matriz, n) returns a list of column values n.
Implementing, we have:
def getLinha(matriz, n):
return [i for i in matriz[n]] # ou simplesmente return matriz[n]
def getColuna(matriz, n):
return [i[n] for i in matriz]
mat1 = [[2, 3], [4, 6]] # uma matriz 2x2
mat1lin = len(mat1) # retorna 2
mat1col = len(mat1[0]) # retorna 2
mat2 = [[1, 3, 0], [2, 1, 1]] # uma matriz 2x3
mat2lin = len(mat2) # retorna 2
mat2col = len(mat1[0]) # retorna 3
matRes = [] # deverá ser uma matriz 2x3
for i in range(mat1lin):
matRes.append([])
for j in range(mat2col):
# multiplica cada linha de mat1 por cada coluna de mat2;
listMult = [x*y for x, y in zip(getLinha(mat1, i), getColuna(mat2, j))]
# e em seguida adiciona a matRes a soma das multiplicações
matRes[i].append(sum(listMult))
print(matRes)
Run the generated code as output [[8, 9, 3], [16, 18, 6]].
Using classes would be more practical:
class Matriz:
def __init__(self, mat):
self.mat = mat
self.lin = len(mat)
self.col = len(mat[0])
def getLinha(self, n):
return [i for i in self.mat[n]]
def getColuna(self, n):
return [i[n] for i in self.mat]
# opcional: dar overload no operador de multiplicação
def __mul__(self, mat2):
matRes = []
for i in range(self.lin):
matRes.append([])
for j in range(mat2.col):
listMult = [x*y for x, y in zip(self.getLinha(i), mat2.getColuna(j))]
matRes[i].append(sum(listMult))
return matRes
Run this code using
mat1 = Matriz([[2, 3], [4, 6]])
mat2 = Matriz([[1, 3, 0], [2, 1, 1]])
print(mat1*mat2)
takes off [[8, 9, 3], [16, 18, 6]].
0
You can use the function zip and the list comprehension.
The zip function takes lists and builds a list of tuples with the list members. And list comprehension is a quicker way to write loops is simple.
This is basically the code:
numerosX = [3, 5, 7, 11]
numerosY = [4, 6, 8, 12]
numerosZ = [x*y for x, y in zip(numerosX, numerosY)]
print(numerosZ) # Imprime [12, 30, 56, 132]
Just remembering that matrix multiplication is not enough to multiply element by element. Matrix multiplication will always consider multiplication between a row and a column, causing a 1:4 matrix multiplied by a 4:1 to result in a 1:1, not a 1:4.
Browser other questions tagged python python-3.x matrix
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Have you considered using the
np.matmul(a,b)?– FourZeroFive
Already, but this is for an activity and I have to create a function for it anyway, thank you!
– Pedro Fernandes
Good. I hope you want to do this only to train. Because it doesn’t make much sense. The most appropriate is to use a library like numpy.
– Gabriel Machado