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bajnes@gmail.com
science forum beginner

Joined: 18 Nov 2005
Posts: 1

Posted: Fri Nov 18, 2005 7:11 am    Post subject: Math. function maker urgently required!

Dear Dudes,

Urgently wanted:
Is any software , able to model neumerus X per (Y1, Y2, Y3,...Yn) date
values by a math. function.
e.g. : X= 7.75000E-02 5.77500E-01 1.07750E+00 1.77750E+00 2.07750E+00

Y1=1.4799E-04 1.9206E-05 1.1978E-06 9.7149E-10 3.4080E-13

Y2=3.9492E-04 6.0642E-05 5.1197E-06 1.6097E-08 1.1566E-10

Y3= ...
and so on.

Looking for a function (not polynomial, serie,... but a final algebraic
function like: Yn=a.Ln(-b.X+c) or some final formula which can model
such behviors. No matter how many coefficient this function may have.
of course each Yn differs with other by some constants.

Already known that aimed eq. is not linear, and not sure if matlab
could do what we want, or?

Best regards,
Bernard Luis
Robert B. Israel
science forum Guru

Joined: 24 Mar 2005
Posts: 2151

Posted: Fri Nov 18, 2005 8:09 am    Post subject: Re: Math. function maker urgently required!

<bajnes@gmail.com> wrote:

 Quote: Urgently wanted: Is any software , able to model neumerus X per (Y1, Y2, Y3,...Yn) date values by a math. function. e.g. : X= 7.75000E-02 5.77500E-01 1.07750E+00 1.77750E+00 2.07750E+00 Y1=1.4799E-04 1.9206E-05 1.1978E-06 9.7149E-10 3.4080E-13 Y2=3.9492E-04 6.0642E-05 5.1197E-06 1.6097E-08 1.1566E-10 Y3= ... and so on. Looking for a function (not polynomial, serie,... but a final algebraic function like: Yn=a.Ln(-b.X+c) or some final formula which can model such behviors. No matter how many coefficient this function may have. of course each Yn differs with other by some constants.

Ln is not an algebraic function, a polynomial is. But anyway, you might
guess a form for your function with a couple of parameters and use linear or nonlinear
least-squares, as appropriate, to fit it. Since the function values vary widely in
magnitude while apparently being positive, you might try to fit ln(Yn) rather than
Yn directly. Perhaps something like ln(Yn) = a X^2 + b X + c (which you can do by
linear least-squares), resulting in Yn = exp(a X^2 + b X + c).

 Quote: Already known that aimed eq. is not linear, and not sure if matlab could do what we want, or?

Matlab should be perfectly capable of this.

Robert Israel israel@math.ubc.ca
Department of Mathematics http://www.math.ubc.ca/~israel
University of British Columbia Vancouver, BC, Canada
Huynh
science forum beginner

Joined: 18 Nov 2005
Posts: 1

 Posted: Fri Nov 18, 2005 8:57 am    Post subject: Re: Math. function maker urgently required! you should use function: lsqcurvefit(...) of matlab. It is very useful.

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