Re: help finding define_counts()

Does ISIS adjust the stored error/uncertainty at any time besides when
define_counts is called?

For example, if I say:

variable oMSE = Minimum_Stat_Err;
Minimum_Stat_Err = 1.e-100;
define_counts(....);
Minimum_Stat_Err = oMSE;
% Go about business...

Will this have unexpected consequences of changing my error bars down 
the road?

Thanks,
Rob


Quoting John Houck <houck_at_email.domain.hidden
> On Fri, Mar 21, 2008 at 04:14 +0100, Manfred Hanke wrote:
>>
>> continuing the suggestions of Mike, one could also add some
>> documentation on the variable Minimum_Stat_Err. When it's not an
>> counts-Spectrum one wants to fit, one has often to set it to a value
>> much lower than 1, perhaps even DOUBLE_MIN.
>>
>
> When a dataset is being treated as "counts", isis attempts to
> validate the input uncertainty values, requiring them all to be
> greater than or equal to Minimum_Stat_Err, where
> Minimum_Stat_Err has a default value of 1.
>
> For example, defining a single-bin "counts" dataset with has
> bin value 1.e-5 and uncertainty 1.e-8:
>
> isis> define_counts (1.0, 2.0, 1.e-5, 1.e-8);
> 1
> isis> print(get_data_counts(1).err);
> 1
>
> Note that isis "corrected" the 1.e-8 uncertainty value because
> it was inconsistent with default expectations for this kind of
> data.
>
> To force isis to retain positive counts-uncertainty values that
> "look wrong", define a minimum (positive) allowable uncertainty
> value using Minimum_Stat_Err:
>
> isis> Minimum_Stat_Err=1.e-20;
> isis> define_counts (1.0, 2.0, 1.e-5, 1.e-8);
> 2
> isis> print(get_data_counts(2).err);
> 1e-08
>
> Here, isis kept the 1.e-8 uncertainty value.
>
> When data is declared to have "flux" values, this kind of
> filtering does not take place:
>
> isis> define_flux (1, 2, 1.e-5, 1.e-8);
> 1
> isis> print(get_data_flux(1).err);
> 1e-08
>
> Uncertainties for flux values are required to be positive, but
> that's the only constraint.
>
> I'll include this explanation in the manual.
>
> Thanks,
> -John
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