Recent content by evgenx

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    Solving Problem to Get Unnormalized Eigenvectors in C/Fortran

    Hi All, Many thanks for your replies ! Concerning the solution with Mathematica it is of course very nice but unfortunatelly I cannot use it. I need a subroutine in C or fortran because I have to embed it in a code (written in C/fortran). Sorry, that I was imprecise in my post concerning the...
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    Solving Problem to Get Unnormalized Eigenvectors in C/Fortran

    Hallo, I am trying to solve the following problem. I need to get eigenvectors of a matrix. I know that there are many subroutines for that in linear algebra packages, for instance in Lapack there is DSPEV, but they all give normalized eigenvectors, while I need the "original" unnormalized ones...
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    Analytical form of an Interpolated function

    Are you sure? As far as I remember, in the manual, it is written that one can work with "interpolated" functions like with normal functions. So it should be a function. Ok, I might try to represent my "Interpolated" function with a polynomial, via 1s,2nd etc derivatives. Maybe it will work...
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    Analytical form of an Interpolated function

    Yes, as far as I know Mathematica does not output automatically the formula of the function obtained with "Interpolation". I am sure that this issue has been posted before at the forum but unfortunately I cannot find the thread :frown:
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    Analytical form of an Interpolated function

    Analytical form of an "Interpolated" function Hallo, I have a question on the use of "Interpolation" function in Mathematica. I am wondering whether it is possible to extract an analytical expression for a function built using the "Interpolation" option. Say, I have the following function...
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    Mathematica Minimum function path on a surface with Mathematica

    Hi Bill Simpson and Jackmell, Thanks a lot for your replies. The surface actually looks smooth if you just plot f[a,b]; I mean Plot3D[f[a,b],{a,160,210},{b,160,210}]. Well, to run trajectories on that surface one should solve a set of 4 equations, i.e. two conjugated pairs (coordinate and...
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    Mathematica Working with functions defined by Interpolation in Mathematica

    Working with functions defined by "Interpolation" in Mathematica Hello, Just perhaps a simple question for a Mathematica expert: I have a function of two variables f(a,b) defined using Interpolation option in Mathematica. I am wondering how to determine the value of one of the variable...
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    Mathematica Minimum function path on a surface with Mathematica

    Hi, thanks for your response. Here are some more details on the problem (sorry that I didn't give them in the first post): the surface is defined as follows: surf=Interpolation[{ {{150.0, 150.0}, 3.096864}, {{150.0, 160.0}, 3.046994}, {{150.0, 170.0}, 3.009620}, {{150.0, 180.0}...
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    Mathematica Minimum function path on a surface with Mathematica

    Hello, I am trying to solve the following problem using Mathematica: I have (defined) a surface of two variables, say f(a,b). Now I want to plot a path (a line) that corresponds to min[f(a,b)] starting from certain valus of a and b (say a0,b0). In other words the path always proceeds...
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    Plotting an intersection seam on a contour plot ?

    Hi, I have two 2D functions (surfaces), s1(x,y) and s2(x,y) defined via Interpolation. They intersect forming an intersection seam (which is a line). I can plot both functions using Plot3D and I can also plot the seam on the same 3D plot by means of the MeshFunctions option. The comand I...
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    Mathematica Partial derivative of an interpolated function (with Mathematica)

    Great, everything works! Thanks a lot! A-a, just the very last question ... When I tried to plot da and dada (with Plot3D) they looked like the function (surf) has discontinuities at a=180.0. I guess it has to do with the quality of interpolation. After I added Method->"Spline" (as an...
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    Mathematica Partial derivative of an interpolated function (with Mathematica)

    Hi, Many thanks for your reply. It works now fine. Well, there is an additional related question. Namely, I'd like to find a point on the surf[a,b] (i.e. values of a and b) where both dsurf/da=0 and d²surf/da²=0. Just simply solving: s1=Function[{a,b},surf[a,b]]...
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    Mathematica Partial derivative of an interpolated function (with Mathematica)

    Hi, I faced a problem (in Mathematica) when trying to plot a partial derivative of a functiona (of two variables) obatined by "Interpolation". More precisely, here is my input: surf=Interpolation[{ {{160.0, 160.0}, 2.852688}, {{160.0, 170.0}, 2.827547}, {{160.0, 180.0}, 2.818931}...
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