Chris Jillings wrote:
>
> Hello,
> This point is a fine detail, but it may be important to me.
> >From reading Fred James'reference manual for version 94.1 of Minuit, I
> find on page 9 a list of iflag values used in the call to FCN. It has I
> flag = 1,2, and 3 (see page 9). It seems that FCN is called with iflag=1
> for startup. So I test on iflag, as in the example, and so some
> initialization there.
>
> But when I run TMinuit, I get the following output (having sent print
> level to 3.)
> **********
> ** 4 **MIGRAD 500 1
> **********
> FIRST CALL TO USER FUNCTION AT NEW START POINT, WITH IFLAG=4.
> START MIGRAD MINIMIZATION. STRATEGY 1. CONVERGENCE WHEN EDM .LT.
> 1.00e-03
> FCN=-0.519027 FROM MIGRAD STATUS=INITIATE 21 CALLS 22
> TOTAL
>
> What does IFLAG=4 mean? "First call to use function" suggests to me that I
> should test on iflag==4 to do my initializations.
>
> Thank you for any help.
The convention used by MINUIT is the following:
- IFLAG=1 when FCN is called for the first time.
- IFLAG=2 if you have specified the option to calculate GRAD,
the first derivatives (optional)
- IFLAG=3 call to FCN when the fit is finished.
- IFLAG=4 normal calls to FCN during the minimization process
The Minuit documentation at page 9 shows an example of FCN
with tests on IFLAG=1,2 or 3. IFLAG=4 is not explicitly quoted,
but from the simple example, on can deduce that this is the normal
call.
Rene Brun
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