Neil Traft
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 Feb25 comment What exactly is the difference between a derivative and a total derivative? Do you know what the answer was? I keep getting $2r$ even when using Arkamis' formula. Jan20 accepted How to deal with x/|x| in an equation? Jan19 asked How to deal with x/|x| in an equation? Sep23 comment How to take the gradient of the quadratic form? To help future generations: the full specification of the chain rule used here is $$\frac{df(g,h)}{dx} = \frac{d(g(x)^T)}{dx} \frac{\partial f(g,h)}{\partial g} + \frac{d(h(x)^T)}{dx} \frac{\partial f(g,h)}{\partial h}$$ The order of multiplication is very important since we're dealing with vectors! Sep12 comment Texbook with proof that product of two Gaussian functions is also Gaussian Unfortunately John's blog post doesn't contain the full derivation. Would anyone like to contribute a line-by-line proof? Or cite a textbook that has one? Dec2 comment What exactly is the difference between a derivative and a total derivative? OP: Did they say that your answer was wrong, or only that you solved it using the wrong method? Jun20 awarded Autobiographer Mar27 awarded Student Mar27 awarded Scholar Mar27 awarded Editor Mar27 comment How is it that some forms of an equation can have a defined outcome while other forms of the same equation are undefined? Thinking back, I now realize that I've tripped over this problem again and again when evaluating algebraic expressions. Are there some basic rules to keep in mind to stop me from making illegal steps?? Or would I have to study this whole branch of mathematics to know the difference? :-P Mar27 accepted How is it that some forms of an equation can have a defined outcome while other forms of the same equation are undefined? Mar27 revised How is it that some forms of an equation can have a defined outcome while other forms of the same equation are undefined? added 107 characters in body Mar27 asked How is it that some forms of an equation can have a defined outcome while other forms of the same equation are undefined? Jan2 awarded Supporter