Finding a variable in a equation

Please, I'm new to MATLAB and I want to know how to solve a problem.

I have two variables with 2000 values (I choose 10 to put here):

x = [ 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 ];

y = [-3.6621 7.32421 -1.831054 -1.831054 -7.32421 3.6621 -1.83105 0.00023 0.00847]

These variables are in the equation: y = K((e^(x/25)) − 1)

I have to use Ordinary least squares (linear regression) or Semilogarithmic plot to find the "K" with the informations above of x and y.

If I choose linear regression I can use these functions: fit, fittype,fitoptions.

Thanks!

Answer 1

[Michael Bouser]

First, apply a little algebra. Rewrite your equation in the form "K=". You are going to need to isolate your variable.

Next, because you are using vector inputs, make sure you use ".*" or "./" to force Matlab to do the math "element by element" if you expect an answer in the form of a vector. I think you need to use exp() to do the "e^" part.

It looks like you are doing ok with using parentheses to "maintain order".

[Befs .07]

Actually, I have 2000 values of x and y (I choose 5 to put there) and I have to use Ordinary least squares Method. I can use these functions: fit, fittype,fitoptions.

Thanks for all!

Answer 2

[Roger Stafford]

The following obtains a least squares value for K:

   K = y/(exp(x/25)-1);

I am assuming x and y are still row vectors here and of the same length.

[Star Strider]

‘Befs .07’ is constrained to using fit, fittype, and fitoptions.

[Roger Stafford]

Well, if ordinary least squares are called for, do this:

   t = exp(x/25)-1;
   K = sum(y.*t)/sum(t.^2);