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Category: Mathematics

Mathematics

Horn’s inequality for singular values via exterior algebra

Posted on December 29, 2015 by wj32 / 0 Comment

\( \DeclareMathOperator{\tr}{tr} \DeclareMathOperator{\sgn}{sgn} \DeclareMathOperator{\Id}{Id} \)Horn’s inequality states that for any two compact operato...

Mathematics

Line integrals: 3. Applications to complex analysis

Posted on June 10, 2013 by wj32 / 2 Comments

\( \newcommand{\bbc}{\mathbb{C}} \newcommand{\Int}{\operatorname{Int}} \)Navigation: 1. Exact, conservative and closed forms | 2. Locally exact forms and singul...

Mathematics

Line integrals: 2. Locally exact forms and singular homology

Posted on June 3, 2013 by wj32 / 6 Comments

Navigation: 1. Exact, conservative and closed forms | 2. Locally exact forms and singular homology | 3. Applications to complex analysis As in part 1, \(E,F\) a...

Mathematics

Line integrals: 1. Exact, conservative and closed forms

Posted on June 1, 2013 by wj32 / 11 Comments

Navigation: 1. Exact, conservative and closed forms | 2. Locally exact forms and singular homology | 3. Applications to complex analysis The line integral is a ...

Mathematics

First-order ODEs, matrix exponentials, and det(exp)

Posted on March 11, 2013 by wj32 / 0 Comment

Last time we derived a formula for the derivative of the matrix exponential. Here we will be focusing instead on the expression $$D\exp(x)u=\exp(x)u=u\exp(x),$$...

Mathematics

Fréchet derivative of the (matrix) exponential function

Posted on February 28, 2013 by wj32 / 2 Comments

$$ D\exp(x)u = \int_0^1 e^{sx}ue^{(1-s)x}\,ds. $$ This intriguing formula expresses the derivative of the exponential map on a Banach algebra as an integral. In...

Mathematics

Convex functions, second derivatives and Hessian matrices

Posted on February 26, 2013 by wj32 / 1 Comment

In single variable calculus, a twice differentiable function \(f:(a,b)\to\mathbb{R}\) is convex if and only if \(f^{\prime\prime}(x)\ge 0\) for all \(x\in(a,b)\...

Mathematics

Differentiation done correctly: 5. Maxima and minima

Posted on February 25, 2013 by wj32 / 1 Comment

Navigation: 1. The derivative | 2. Higher derivatives | 3. Partial derivatives | 4. Inverse and implicit functions | 5. Maxima and minima In this final post, we...

Mathematics

Differentiation done correctly: 4. Inverse and implicit functions

Posted on February 24, 2013 by wj32 / 0 Comment

Navigation: 1. The derivative | 2. Higher derivatives | 3. Partial derivatives | 4. Inverse and implicit functions | 5. Maxima and minima Now we’re going ...

Mathematics

Differentiation done correctly: 3. Partial derivatives

Posted on February 23, 2013 by wj32 / 0 Comment

Navigation: 1. The derivative | 2. Higher derivatives | 3. Partial derivatives | 4. Inverse and implicit functions | 5. Maxima and minima While we saw that diff...

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