Q. regarding optim()
On Fri, 21 Jul 2006, N. Goodacre wrote:
Dear R mailing group,
The second parameter for the function optim()is a function whose
parameters are to be optimized. The description of this function given in
the help file is the following:
fn: A function to be minimized (or maximized), with first
argument the vector of parameters over which minimization is
to take place. It should return a scalar result.
Let's say the second argument is x, a vector of x values
But it says `parameters'. Please look at the examples on that help page. optim is concerned with optimizing functions of more than one parameter. In a statistical setting 'x' may be the data, but e.g. for fitting a gamma distribution c(scale, shape) are the parameters.
I would have thought that fn should return a vector full of y values for the x values entered as the second argument. If the function just takes one value at a time and outputs a scalar, how can I specify for fn which x value, of the vector x, to take? Sincerely, Norman Goodacre
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