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# 61 Actions

 Aug18 revised Integro-differential equation An educated guess what the formula should original look like (it is a diffusion equation) Aug18 suggested approved edit on Integro-differential equation Aug14 awarded Enlightened Aug12 comment Change variables in differential expressions I do not think the chain rule is applied correctly. If I use expr[r_]:=D[b[r],r] and then evaluate expr[1/x] I get b'[x] and not -b'[x] x^2... Aug12 awarded Critic Jul11 comment How can I get Mathematica to simplify $\Vert\{1,\sin(t),\cos(t)\}\Vert_2$ to $\sqrt{2}$? @term-rewritica: no, you are right $\cos^2 x + \sin^2 x$ is always 1. However $|\cos x|^2+ | \sin x|^2$ is not always equal to 1. Jun12 accepted Incorrect results for elementary integrals when using Integrate Jun12 awarded Nice Answer Jun6 comment How can I eliminate a function in a system of PDEs, Maple-style? An even easier question would be: how can one eliminate a function in a set of ordinary differential equations using Mathematica. Jun5 awarded Commentator Jun5 revised Different determinants on 2 different computers added 1 characters in body Jun5 comment Different determinants on 2 different computers @Öskå: Eigenvalues[{A,B}] solves the problem $\det(A - \lambda B)=0$ for $\lambda$; however in a numerically stable version unlike writing down the polynomial equation for $\lambda$ and then solving it... Jun4 answered Different determinants on 2 different computers May4 comment Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a Thank you: this is exactly the problem I was suffering. In fact, I did know that Flat affects the pattern matching but I did not know that for a pattern only the attributes at the time when it is set are important and that the attributes are then stored. May3 accepted Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a May3 comment Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a Thanks for your question. I figured out that my example was a bit to minimal. I changed the question such that now it is clear where the infinite recursion appears. May3 revised Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a deleted 59 characters in body; edited title May3 comment Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a Sorry for the confusion. I tried to find a minimal example and it was too minimal (and I did not see that some old Attributes were still set). I edit the question... May3 revised Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a added 205 characters in body May3 comment Constructing a function with Flat and OneIdentity attribute with the property that otimes[a]:>a @Rojo: otimes[anything]