morgan

 69 Do complex numbers really exist? 34 Inverse of an invertible triangular matrix (either upper or lower) is triangular of the same kind 17 Is reducing a matrix to row echelon form useful at all? 15 Polynomial fitting where polynomial must be monotonically increasing 14 Interesting results easily achieved using complex numbers

### Reputation (2,018)

 +20 Inverse of an invertible triangular matrix (either upper or lower) is triangular of the same kind +10 Is there a polynomial-time algorithm returning a vertex of the feasible region? +10 If $A,B$ symmetric positive semidefinite, show tr$(AB) \geq 0$ +10 Optimization over union of convex sets

### Questions (4)

 7 Bounded, non-constant harmonic functions: how far are they from existing? 2 Liouville's theorem via contraction mappings 1 Can polynomial-exponential sums have an infinite number of zeros in an interval? 0 Measures of subsets of a measurable set

### Tags (49)

 85 linear-algebra × 12 15 polynomials 55 matrices × 9 15 regression 38 inverse × 2 10 algebra-precalculus 15 interpolation 9 popular-math 15 data-analysis 8 soft-question × 4

### Bookmarks (33)

 102 How can I understand and prove the “sum and difference formulas” in trigonometry? 101 Why is the volume of a sphere $\frac{4}{3}\pi r^3$? 86 Intuitive explanation of Cauchy's Integral Formula in Complex Analysis 80 Is there a function with a removable discontinuity at every point? 68 Convergence of $\sqrt{n}x_{n}$ where $x_{n+1} = \sin(x_{n})$