Timeline for Questions on symmetric Hadamard matrices
Current License: CC BY-SA 4.0
9 events
| when toggle format | what | by | license | comment | |
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| Aug 5 at 1:39 | vote | accept | user369335 | ||
| Aug 14 at 7:09 | |||||
| Jun 13 at 12:32 | answer | added | user369335 | timeline score: 4 | |
| Jun 8 at 23:14 | history | edited | user369335 | CC BY-SA 4.0 |
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| Jun 8 at 12:26 | comment | added | Fedor Petrov | Orthogonality means $A A^T=nI$ (where $I$ is identity matrix), if $A^T=A$, we get $A^2=nI$, thus eigenvalues of $A$ are only $\pm \sqrt{n}$. Therefore, if $n$ is not a perfect square, the sum of eigenvalues (i.e., trace) can be integer only if it is 0. | |
| Jun 8 at 12:23 | history | edited | user369335 | CC BY-SA 4.0 |
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| Jun 8 at 12:22 | comment | added | user369335 | The skew-symmetric definition here is slightly different than $A^T=-A$. @FedorPetrov | |
| Jun 8 at 12:17 | history | edited | user369335 | CC BY-SA 4.0 |
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| Jun 8 at 12:09 | comment | added | Fedor Petrov | How can it be skew-symmetric, should not skew-symmetric matrix have zeros on diagonal? | |
| Jun 8 at 11:39 | history | asked | user369335 | CC BY-SA 4.0 |