rcollyer
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 Jun8 awarded Caucus Apr18 awarded Promoter Apr16 asked Generating the partners in a multi-dimensional irreducible representation. Jan30 comment Pythagorean Theorem Proof Without Words (request for words) Brilliant. Nice answer. Nov23 comment Compute $\mathbf v \mathbf A^{-1}\mathbf v^\top$ in a numerically stable way I found cholesky in the parallel directory: decompositions. Nov23 answered Compute $\mathbf v \mathbf A^{-1}\mathbf v^\top$ in a numerically stable way Nov21 revised Finding the derivative of two integrals and establish their equality. reworded title Nov21 suggested approved edit on Finding the derivative of two integrals and establish their equality. Nov17 comment Possible bug in Mathematica? Also, Integrate doesn't do anything with an integer assumption (see the comments), so you have to watch out for them yourself. Nov17 comment Possible bug in Mathematica? Sorry, mixing messages there. $\int^\pi_{-\pi} \cos(qx) = 2$ when $q = 0$, but $0$ otherwise. But, you get the wrong answer if you integrate first and then set $q=0$. So, I was wondering if we're running into something similar with regards to $r$ in your integrals, but I didn't write it out as fully as I should have. Nov17 comment Possible bug in Mathematica? I have no idea why it ends being the exact negative. A guess is that like $\int^\pi_{-\pi} \cos(qx)$ with $q\in\mathbb{Z}$, there are multiple solutions depending on $r$, and by not fixing its value, Mathematica blithely chooses the incorrect one. Nov17 answered Taking advantage of linearity of integration in Mathematica Nov17 comment Possible bug in Mathematica? Some quick notes. Symbolically integrating both pieces, I get (-i r^2 + r^(3/2) (i FresnelC[Sqrt[r]] + FresnelS[Sqrt[2]]))/Pi for $\int f$ and its negative for the second integral. However, integrating them both with a definite value of $r$, I get different results. For $r=5$, the sum is $1.19-5.00i$, and for $r=6$, the sum is $3.30-9.00i$, rounded, of course. I wonder if this is similar to the problem of integrating $\cos(q x)$ with $q \in \mathbb{Z}$. Nov16 comment How to solve integral in Mathematica? Can you do me a favor and give some details as to the mathematics problem you're trying to solve? If we can understand what it is you're trying to accomplish, we may be able to provide better answers. Nov16 comment How to make Runge-Kutta for solving nonlinear ODE system in Mathematica @George, I just downloaded your notebook, and in it you're using the form \[DifferentialD]f/\[DifferentialD]t which is incorrect as DifferentialD has no meaning by itself. Instead, you're looking for \[PartialD]. Nov15 comment How to make Runge-Kutta for solving nonlinear ODE system in Mathematica @Georde, also the NDSolve plug-ins tutorial gives explicit detail of setting up an RK4 integration. Admittedly, not all of it is germane to your question, but it does lay out the algorithm for you. Nov15 comment Group under matrix multiplication As an added point, since your inverse did not have the same form as the other elements of the group, you should have been immediately suspicious of it, especially since you have already proven closure. Nov15 revised Group under matrix multiplication added align to bring eqns inside bounding box. Nov15 suggested approved edit on Group under matrix multiplication Nov12 awarded Fanatic