[R] fitting cosine curve

Don Cohen don-r-help at isis.cs3-inc.com
Wed Jun 21 03:37:57 CEST 2017

If you know the period and want to fit phase and amplitude, this is
equivalent to fitting a * sin + b * cos

 > >>> > I don't know how to set the approximate starting values.

I'm not sure what you meant by that, but I suspect it's related to
phase and amplitude.

 > >>> > Besides, does the method work for sine curve as well? 

sin is the same as cos with a different phase
Any combination of a and b above = c * sin (theta + d) for
some value of c and d and = e * cos (theta + f) for some value
of e and f.
Also for any c,d and for any e,f there is an a,b.
the c and e are what I'm calling amplitude, the d and f are what
I'm calling phase.

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