Timeline for How to characterize real square matrices A, such that v'Av >= 0, for all real vectors v with 1'v=0 (1 is the vector of all ones)?
Current License: CC BY-SA 2.5
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| Nov 4, 2010 at 3:59 | comment | added | Will Jagy | Gerry, the first thing is to take the symmetric part, when $ A = A_1 + A_2$ with $A_1$ symmetric but $A_2$ skew symmetric, his quadratic form is not changed by taking $A_1.$ A correct but useless answer is to demand an orthogonal change of basis to a basis with first vector parallel to $(1,1,\ldots,1).$ Then he wants the block referring to the next $n-1$ vectors positive semidefinite. | |
| Nov 4, 2010 at 3:52 | history | answered | Gerry Myerson | CC BY-SA 2.5 |