Recent content by evgenx

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...

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...

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...

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:

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...

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...

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...

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}...

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...

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...

Ok, I see. Thanks again for your help!

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...

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]]...

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}...