[R] Please Please Help me!!!

[Gabor Grothendieck]

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On 7/15/07, TIMMMAY <ed_deroiste at yahoo.co.uk> wrote:
>
> I posted the message below a few days ago but I have not had any responses. I
> keep thinking that there must be some easy way to answer the problem I am
> just not familiar enough with regression to answer the problem myself. If
> anyone can help me I would be very grateful. I need to fit a gamma curve to
> a set of data. ie a scatterplot of the data indicates that the curve looks
> like a truncated gamma density function and I would like to estimate the
> paramaters so that I can fit a curve to the data points. Its not MLE
> paramater estimation just a curve fitting exercise. The problem again is
>
> I have a set transition intensities and when plotted the curve looks like a
> gamma density. I want to fit a gamma density curve to these intensities. It
> is just a curve fitting problem but whats causing the trouble is that I need
> to use least squares minimization to calculate the parameters for the gamma
> curve. How do I do this???
>
> The curve will be a truncated gamma function so it will have 3 paramaters a,
> b, c. I tried to do the following
>
> nls(lograte ~ log(c) + a*log(b) + (a-1)*log(age)+b*(age)-lgamma(a),
> start=list(a=1,b=1,c=1)), where lograte, and age are my data. a,b the gamma
> parameters and c the parameter we need because we are fitting a truncated
> distribution.
>
> I also tried defining
> fn = function(p) sum((log(y)-log(dgamma(x,p[1],p[2])*p[3]))^2)
> a residual sum of squares and using nlm to minimise this and find paramaters
> but this doesnt work either. Can anyone help me ?? Please :)
>
> Original message follows :(
> Fitting a Gamma Curve
> by TIMMMAY Jul 12, 2007; 03:38pm :: Rate this Message:    (use ratings to
> moderate[?])
>
> Reply | Reply to Author | Show Only this Message
>
> Hi there, I hope someone can help me before I tear all my hair out. I have a
> set transition intensities and when plotted the curve looks like a gamma
> density. I want to fit a gamma density curve to these intensities. It is
> just a curve fitting problem but whats causing the trouble is that I need to
> use least squares minimization to calculate the parameters for the gamma
> curve. How do I do this???
>
> The curve will be a truncated gamma function so it will have 3 paramaters a,
> b, c. I tried to do the following
>
> nls(lograte ~ log(c) + a*log(b) + (a-1)*log(age)+b*(age)-lgamma(a),
> start=list(a=1,b=1,c=1)), where lograte, and age are my data. a,b the gamma
> parameters and c the parameter we need because we are fitting a truncated
> distribution.
>
> I also tried defining
> fn = function(p) sum((log(y)-log(dgamma(x,p[1],p[2])*p[3]))^2)
> a residual sum of squares and using nlm to minimise this and find paramaters
> but this doesnt work either. Can anyone help me ?? Please :)
>
>
>
>
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