Solving numerically one equation and data fit

Forum|Forum|6 years ago
April 7, 2020
1 reply
4205 views

Hello Everyone,

I have some experimental points, and I need to fit this with a equation. But the dependence of variables is related wtih a second equation. The problem is explained in the attached file.

Can somebody help me?

Thanks

1_doubt.pdf

L

LucMeekes

23-Emerald IV

Let's establish that the following is known:

Furthermore these equations are given:

Using the first, we can write A as a function of r:

but we can also write r as a function of A:

And that is much more useful, because we cannot write r as a function of CT, but CT as a function of r solves as:

Using this we can substitute r with its function of A, and substitute the third function as well:

So now we have a function CT(A, A0, A1, CBP, K, N).

If the supposed solution is entered, and compared to the known points, we get:

The 'solution' is nowhere near the known points (except for CT=0).

Let's see if we can get a better approximation:

That's more like it.

With these results as guess values, one more try:

I hope this brings you further.

Success!
Luc

W

Werner_E

25-Diamond I

As far as I understand it, is CBP not a value to solve for but should be of constant value 48500.

And the supposed value for A1 is not -20, but should be around +20.

You may consider using a solve block function (or using the root command) to create a function r(CT,K,N) and use this function with equation (1) in a solve block with minerr(K,N,A1).
But I am not sure that the problem is well conditioned.