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 Feb 27 answered Vector multiplication with scalars Jan 21 comment A Projection Problem in Functional Analysis - Uniqueness of a Solution @JonasT: Thank you for your thoughts! By the dual I mean it in the sense as in the Dirac notation, en.wikipedia.org/wiki/Bra-ket_notation . What you meantion in your second comment is exactly the problem. If $\alpha$ and $\beta$ are just constants (as I might not have pointed out very direct), taking the Fourier transform and dividing, they will be functions... This is one thing I am puzzled with :) Greets Jan 20 asked A Projection Problem in Functional Analysis - Uniqueness of a Solution Jan 20 comment Fourier Transform of an unsteady function Thank you for the further clarification. Jan 19 comment Fourier Transform of an unsteady function @loenbloy: Thank you for your fast response. I think the three given ones make a pretty decent picture of the situation, all from a slightly different perspective :) Greets Jan 19 accepted Fourier Transform of an unsteady function Jan 19 comment Fourier Transform of an unsteady function Thank you for this answer and the additional information. I think there was a brain overflow in understanding where the $\delta$ comes from :) Greets Jan 19 comment Fourier Transform of an unsteady function Thank you again for the clarification! I now know that there is a difference in these two approaches :) Greets Jan 19 comment Fourier Transform of an unsteady function Thank you for your answer. I must admit that I never had any course on measure theory so I have to speculate that I really want to calculate the first version. Greets Jan 19 asked Fourier Transform of an unsteady function Jan 19 answered Simple Harmonic Oscillator Solution Jan 19 comment Mathematical difference between white and black notes in a piano Please, Rudi, it should be Helmhol t z. :) Jan 18 comment Effect of curvature of spacetime on intrinsic geometric properties (under general relativity) @Steven: Thank you for your further thoughts. First of all I have to state that the choice of a timeslice would be the gauge I was referring to - hence angles will depend on this choice. Second of all the author is referring to lines of sight - I would interprete these as light geodesics. So, to maybe find a compromise here: One could define such angles more generally but they would depend on the gauge. Is this along your lines of thought? Greets Jan 18 awarded Revival Jan 18 comment Effect of curvature of spacetime on intrinsic geometric properties (under general relativity) @Steven: Thank you for your thoughts - I am not sure if I get them correctly, though. Assuming you are in a dynamic spacetime you can go from A to B to C on some geodesic. How do you go to A from C? It wont be possible with respect to causality. So you will have to define an equivalence class of points A - but in a dynamical spacetime this construction will be due to a certain gauge - your angle will depend on this as well. I wanted to leave out these things for simplicity. Greets Jan 18 comment Writing an Integral in Different Form? @Willie Wong: Thanks you, I wrote small $n$'s if I remember correctly. Greets Jan 18 comment Effect of curvature of spacetime on intrinsic geometric properties (under general relativity) @Ronaldo: Now looking at the comments I think I have just done what you had in mind :) Greets Jan 18 answered Writing an Integral in Different Form? Jan 18 answered Effect of curvature of spacetime on intrinsic geometric properties (under general relativity) Jan 14 comment Eigenfunctions of the Helmholtz equation in Toroidal geometry @Hans Lundmark: Thank you for the hint. I just found the book in our library and will have a look. Is this a classic like the Courant-Hilbert?