calculation iterations

[jakies123]

Hi I calculated Θ,f(Θ),f'(Θ) but I do not know if is possible calculation method Θn if yes how should it ?

[MrShorty]

I'm not sure I understand your question. If I understand the pictured document, it seems like a basic Newton-Raphson type algorithm for finding theta.

The "standard" approach to NR type algorithms in Excel is to use Goal Seek or Solver, since this kind of root finding algorithm is already programmed into those utilities.
Goal Seek: https://support.office.com/en-us/art...3-4f369d6e66c7
Solver: https://support.office.com/en-us/art...B-F63E45925040
I generally prefer to use Solver over Goal Seek, as I find that Solver's algorithms seem more robust. The main advantage here is that you don't need to program f' or other details of the root finding algorithm. You need only enter your best first guess at theta, then enter f(theta), and invoke Solver/Goal Seek to set f(theta) to a value of 0 by changing theta. Solver/Goal Seek will take care of f'.

If you are not allowed to use these built in utilities or for whatever reason you feel that you want to program your own NR algorithm, I will refer you to this tutorial I put together https://www.excelforum.com/tips-and-...ind-roots.html . The spreadsheet only versions use circular references to perform the NR iteration. If you prefer, there is also an example (last post) of a VBA UDF that uses the NR algorithm.

Does that help?

[jakies123]

of course you help me I'll think you good unerstood my question I need find theta and yes this is method Newthona .I add the file

[MrShorty]

You did not say which approach you wanted to use, so I tried using Goal seek:

1) Enter 1.487 (or similar) into Q13.
2) Call Gaol Seek and tell it to:
2a) Set cell: Q15
2b) To value: 0
2c) By changing cell: Q17

And it spit out a result (theta is a little larger than 1.487). Will that work?

[jakies123]

hm Could you send me done the file

[MrShorty]

I can't, but I made no significant change to your file. The only change I made was to overwrite the formula in Q15 with a value close to its current value (Enter 1.487 into Q15 or copy -> paste special -> as values). I assume you should have no trouble entering a value into Q15, so what difficulty are you having in calling and executing the Goal Seek command?

[jakies123]

eh
I did not know what the word means "Goal Seek command" and where it find , that's why I had a problem
I've translated and done thanks

[MrShorty]

Language barriers can be a problem on an international forum like this. Glad you got it figure out.