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the tranpose of transpose doed not equals the original matrix

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Hantao Nie
Hantao Nie 2023 年 10 月 30 日
編集済み: James Tursa 2024 年 1 月 23 日
I find that on my data(see the attachment) ,the tranpose of transpose doed not equals the original matrix. This is my code. I donot understand why (a')' does not equals a. My matlab version is R2022a.
load("a.mat")
norm((a')' - a, 'fro')
ans = 140.4280

採用された回答

Walter Roberson
Walter Roberson 2023 年 10 月 30 日
移動済み: Walter Roberson 2023 年 10 月 30 日
You have a broken sparse matrix, probably build by a third-party product, but possibly built by a broken mex file.
load("a.mat")
whos a
Name Size Bytes Class Attributes a 30084x1 157808 double sparse
at = a';
att = at';
whos a at att
Name Size Bytes Class Attributes a 30084x1 157808 double sparse at 1x30084 398472 double sparse att 30084x1 157808 double sparse
mask = att ~= a;
locs = find(mask, 1)
locs = 499
a(locs)
ans =
All zero sparse: 1×1
at(locs)
ans =
(1,1) -0.1000
att(locs)
ans =
(1,1) -0.1000
d = att - a;
max(d(:))
ans =
(1,1) 1
min(d(:))
ans =
(1,1) -1
nnz(imag(d))
ans = 0
  2 件のコメント
James Tursa
James Tursa 2023 年 10 月 30 日
編集済み: James Tursa 2023 年 10 月 30 日
I see that Tim Davis's SPOK has been removed from the FEX. I will write a replacement and upload it when I get some free time, maybe this weekend. Should I call it SPOK for consistency in searches or give it a new name?
Walter Roberson
Walter Roberson 2023 年 10 月 30 日
In view of tomorrow's date, perhaps it should be SPOOK ;-)

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その他の回答 (1 件)

James Tursa
James Tursa 2024 年 1 月 23 日
編集済み: James Tursa 2024 年 1 月 23 日
I finally finished my sparse matrix integrity checker. You can find it in the FEX under the name SAREK (I think you will be able to figure out the inside joke):
Here is what it reports for the posted matrix:
>> sarek(a)
SAREK -- Sparse Analyzer Real Et Komplex , by James Tursa
Compiled in version R2023a (with -R2018a option)
Running in version R2023a
Matrix is double ...
Matrix is real ...
M = 30084 >= 0 OK ...
N = 1 >= 0 OK ...
Nzmax = 9862 >= 1 OK ...
Jc[0] == 0 OK ...
Jc[N] = 9862 <= Nzmax = 9862 OK ...
Jc array OK ...
ERROR: There are 9861 Ir entries out of order or out of range
TO FIX: [M,N] = size(A); [I,J,V] = find(A); B = sparse(I,J,V,max(max(I),M),N);
All stored elements nonzero OK ...
There were ERRORS found in matrix!
ans =
9861
And if you plot the row indexes, you can see that the matrix was built in reverse order since they are all decreasing!
>> [I,J,V] = find(a);
>> plot(I)
After applying the recommended fix and re-plotting you can see that the row indexing order has been corrected:
>> [M,N] = size(a); [I,J,V] = find(a); B = sparse(I,J,V,max(max(I),M),N);
>> sarek(B)
SAREK -- Sparse Analyzer Real Et Komplex , by James Tursa
Compiled in version R2020a (with -R2018a option)
Running in version R2020a
Matrix is double ...
Matrix is real ...
M = 30084 >= 0 OK ...
N = 1 >= 0 OK ...
Nzmax = 9862 >= 1 OK ...
Jc[0] == 0 OK ...
Jc[N] = 9862 <= Nzmax = 9862 OK ...
Jc array OK ...
Ir array OK ...
All stored elements nonzero OK ...
All sparse integrity checks OK
ans =
0
>> [I,J,K] = find(B);
>> plot(I)

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