- #1

- 194

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y=20-a*10*log(x)

My problem is just getting a curve fit to this equation. What function in MATLAB should I be looking for? How do I get the value of 'a'?

Is it easier to achieve this in Excel? How?

- MATLAB
- Thread starter ACLerok
- Start date

- #1

- 194

- 0

y=20-a*10*log(x)

My problem is just getting a curve fit to this equation. What function in MATLAB should I be looking for? How do I get the value of 'a'?

Is it easier to achieve this in Excel? How?

- #2

chroot

Staff Emeritus

Science Advisor

Gold Member

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All of the functions available in that menu are also available on the command line, but I find curve fitting to be much more intuitive when done in a plot window.

- Warren

- #3

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will i be able to enter in my own custom equation? thanks

- #4

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In Matlab I am sure you can enter your custom equations.

- #5

f95toli

Science Advisor

Gold Member

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Yes, you can fit to whatever function you want.will i be able to enter in my own custom equation? thanks

Note that if you use functions from the Optimization toolbox (if you have that installed) you can quite easily fit to a nonlinear Matlab function, i.e. you can "fit" to a piece of code which generates an output that depends on an number of inputs, even if the function includes e.g. interpolation (which is often used conventient when fitting to a large set of experimental data), if-then statements etc. This is often very useful.

Also, if you are able to rewrite your equations as a matrix equation (e.g. a sum of exponentials with unknown prefactors) you can of course also solve it directly, i.e. using something like "X\b" which gives you the best result in the least-square sense.

- #6

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- 0

You can also try Ezyfit, a free curve fitting toolbox for Matlab:

www.fast.u-psud.fr/ezyfit

In your case just type

showfit('y=20-a*10*log(x)')

if your data are plotted in a figure, or

f = ezfit(x,y,'y=20-a*10*log(x)')

if your data are stored into the vectors x,y.

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