Recent content by ballzac

Hey, thanks for all the effort you've gone to. For the purposes of having a heuristic model, I think both of them are 'pretty good' fits. In fact, the uncertainty in those figures is roughly plus or minus the last decimal place (except for the x values which are 1,2,3 etc. divided by 1280...

I'm just curious what results you're actually hoping to compare? If you use nonlinear regression, your results should be exactly the same as mine given the same data. You haven't actually stated what method your using.Here's my data. The first column is the x-axis and the other two columns are...

I'm confused :confused: The plots I posted in #12 included curves fitted using nonlinear regression as well as the associated constants A, p, and C (b, c, and a, respectively, using your convension).

Thanks for the info and links. Some of my data I have very good reason to believe follows a power law, and I'm planning on deriving the relationship analytically at some stage, but some of it I am just guessing. At this stage, I wouldn't even know where to begin working out what the relationship...

Thanks for the recommendation, and thanks for all the help :)

I might have to do some reading as I don't know much about this subject, but yes, for my current purposes I think what I've done will suffice. It actually amazes me how little emphasis there was on data analysis in my undergrad physics studies.

The two data sets are shown as red squares in the upper two plots, with the fitted curves shown in blue. The residuals are shown for each data point under each respective plot. Note the 10^-3 on the y-axis for the residuals. For actually finding a model that explains the data, this might not...

Thanks for posting. I've managed to fit a really nice curve to my data. Plotting the residuals, I see that there is structure that's unaccounted for in my model, but the residuals are very small, so it does provide an accurate 'rule of thumb'. The curve fits better than what I obtained...

Yep, I'm just checking out the nlinfit function in matlab. It seems to be the way to go. The 'guesses' shouldn't be a problem because I can use my 'bad' data from the attempted linear regression as a starting point. Thanks heaps for you help. :)

Thanks for the advice everyone. You are right AlephZero, I forgot to include A, though units aren't an issue because x and y are both dimensionless. So I really have 3 unknowns that I need to work out.

Curve-fitting y=Ax^p+C Howdy, So I have some data that I suspect to follow a y=x^p+C relationship, where p and C are unknown, real numbers. The y values contain some uncertainties, so I want to use a least squares (or similar) method to fit a curve and quantify the goodness of fit. I...

+1 Not all differential geometry courses use tensor notation, so I'd suggest doing one that does. I'm surprised no one has said linear algebra. I'm certainly no expert on GR, but I have studied it and from memory a basic understanding of linear algebra help with some of the manipulation of...

If you're using it as a symbolic variable, you need to define it using syms td; I don't know if there are alternate syntaxes for integrating, but AFAIK it's normally int(expr,var) so your code would be syms td...

I'm having trouble understanding this. Is this all of your code? You don't have a definition for td.

Another thing is, if you start persist with studying physics and find you really don't enjoy it, the problem-solving skills you learn in physics will help you in just about anything you apply it to if you decide to switch. Philosophy, language, history, music theory, computer programming... So...