Strange behaviour computing l1 norm of rows of a matrix
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Christoph Neumann
il 22 Lug 2020
Commentato: James Tursa
il 28 Gen 2024
I have a (1102,8232)-matrix B (from Data that I don't have control over).
The query
B(1102,:)
yields
ans = All zero sparse: 1×8232
However, when I compute
beta = sum(abs(B),2);
or equivalently
beta = vecnorm(B,1,2)
I get
beta(1102)
ans = (1,1) 55
On the other hand, the command
norm(B(1102,:),1)
ans = 0
works as expected.
I'm really confused what's happening here. Any help is appreciated.
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Bruno Luong
il 13 Ago 2020
Modificato: Bruno Luong
il 13 Ago 2020
Who build this sparse matrix B?
If it's build from external source it can be not-valid. I believe there is a tool on FileExchange to validate the sparse matrix, the name escapes me now.
EDIT: this command crahes my MATLAB
B = B+0
indicating this matrix has serious building flaw.
6 Commenti
Bruno Luong
il 13 Ago 2020
Yeah but be aware the fixed matrix might not be correct. You better try to fix at gurobi_read or python, whichever step that is responsible for the error.
James Tursa
il 28 Gen 2024
Note that spok has been removed from the FEX. You can use my replacement function sarek instead:
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