Topic: Fitting normal distribution

I am trying to fit a user defined trend line to my pointset, I have defined it as "(1/$dev*sqrt(2*pi))*e^(-0.5((x-$mean)/$dev)^2)" i.e. the formula for a normal distribution, but it does not seem to want to fit (no solution found). I realise it is probably due to $dev being in the formula twice (since if using two different variables it can fit a graph, but this is not a normal distribution then...) Is there any way to make this work?

Re: Fitting normal distribution

First I think you made a minor mistake in placing one of the brackets. You probably meant this:


It looks like there is a bug in Graph preventing it from handling models correctly when the same constant is used several times in the same model. I wonder why I never noticed that problem myself.

I have now fixed the problem in the beta version of Graph 4.4 at

Alternatively you can use the dnorm function, which should work with Graph 4.3. So you can use this model to create a normal distribution:

dnorm(x, $mean, $dev)

Re: Fitting normal distribution

Thanks a lot. I managed to work around it for my draft assignment due tomorrow by using different variables ($dev and $dev2) (since they came out rather identical anyway), but I shall probably download the beta for when the final one is due. Once again, this program is superb. Now all i need is a simpler way to plot a histogram than defining 12 different straight line functions each on their own small domain and shading each of them down to the x-axis. wink

Re: Fitting normal distribution

You will probably have more luck with a spreadsheet for plotting histograms. I don't think Graph is the proper tool for that.