How do I identify the linearly independent rows of a matrix? For instance,
[[0 1 0 0]
[0 0 1 0]
[0 1 1 0]
[1 0 0 1]]
The 4th row is independent.
First, your 3rd row is linearly dependent with 1t and 2nd row. However, your 1st and 4th column are linearly dependent.
Two methods you could use:
Eigenvalue
If one eigenvalue of the matrix is zero, its corresponding eigenvector is linearly dependent. The documentation eig states the returned eigenvalues are repeated according to their multiplicity and not necessarily ordered. However, assuming the eigenvalues correspond to your row vectors, one method would be:
import numpy as np
matrix = np.array(
[
[0, 1 ,0 ,0],
[0, 0, 1, 0],
[0, 1, 1, 0],
[1, 0, 0, 1]
])
lambdas, V = np.linalg.eig(matrix.T)
# The linearly dependent row vectors
print matrix[lambdas == 0,:]
Cauchy-Schwarz inequality
To test linear dependence of vectors and figure out which ones, you could use the Cauchy-Schwarz inequality. Basically, if the inner product of the vectors is equal to the product of the norm of the vectors, the vectors are linearly dependent. Here is an example for the columns:
import numpy as np
matrix = np.array(
[
[0, 1 ,0 ,0],
[0, 0, 1, 0],
[0, 1, 1, 0],
[1, 0, 0, 1]
])
print np.linalg.det(matrix)
for i in range(matrix.shape[0]):
for j in range(matrix.shape[0]):
if i != j:
inner_product = np.inner(
matrix[:,i],
matrix[:,j]
)
norm_i = np.linalg.norm(matrix[:,i])
norm_j = np.linalg.norm(matrix[:,j])
print 'I: ', matrix[:,i]
print 'J: ', matrix[:,j]
print 'Prod: ', inner_product
print 'Norm i: ', norm_i
print 'Norm j: ', norm_j
if np.abs(inner_product - norm_j * norm_i) < 1E-5:
print 'Dependent'
else:
print 'Independent'
To test the rows is a similar approach.
Then you could extend this to test all combinations of vectors, but I imagine this solution scale badly with size.