[daip] AIPS question: IMFIT vs JMFIT

[lisakov]

Dear Sir,

I have faced a need to perform an image plane fitting of a structure of
an AGN with several Gaussian components. Particularly it is a
multi-epoch stacked image of the 3C273 at 7 mm.

I decided to use AIPS and found 2 tasks which satisfy my needs: IMFIT
and JMFIT.
I found then that these tasks perform differently. With the same
starting model (which is quite a good starting point, I believe) JMFIT
works well but IMFIT complains on strange value of some parameters (I
think, not the initial one, but the one which occurs during the evaluation)
IMFIT1: STRANGE VALUE FOR COMP= 1 PARAM= 4 VALUE= 5.111E+02
IMFIT1: RIDICULOUS VALUE FOR SOME PARAMETER AT NITER= 40
IMFIT1: CHECK INPUT MODEL. MODEL VALUE IS CRAZY

and then "Purports to die of UNNATURAL causes".


Regarding this different behaviour I wonder, are there any caveats of
using JMFIT instead of the IMFIT?

And yet another question. I am not totally satisfied with JMFIT because
I did not manage to make JMFIT use only pure circular Gaussians. I've
tried to let only major axes to vary, but this performs as it should -
it results in elliptical Gaussians. So my question: is there a
possibility to tell JMFIT to use pure circular Gaussian components?


AIPS version is 31DEC14.
Attached to the e-mail are
* image to fit
* commands to set initial parameters and run both IMFIT and JMFIT

Looking forward to see your response.

Best regards,
Mikhail Lisakov.


-------------- next part --------------
* use IMFIT
tge imfit
default
getn 1

ngauss =4
blc 507 500
trc 523 520


dowidth -1
dopos -1 
domax -1

for i = 2 to NGAUSS; dowidth(1,i) = 1; dowidth(2,i) = 1; dowidth(3,i)=-1; end
for i = 2 to 2; dopos(2,i) = 1; dopos(1,i)=1; end
for i = 2 to NGAUSS; domax(i) = 1; end


gpos  512,513,514,511,517,507,520,503
gmax  2.1,3.1,1.5,1
gwidth 1,1,0,1,1,0,3,3,0,3,3,0

go




tge ccntr
getn 1
go

-------------- next part --------------
* use JMFIT
tge jmfit
default
getn 1
ngauss =4
blc 507 500
trc 523 520


dowidth -1
dopos -1 
domax -1

for i = 2 to NGAUSS; dowidth(1,i) = 1; dowidth(2,i) = 1; dowidth(3,i)=-1; end
for i = 2 to 2; dopos(2,i) = 1; dopos(1,i)=1; end
for i = 2 to NGAUSS; domax(i) = 1; end


gpos  512,513,514,511,517,507,520,503
gmax  2.1,3.1,1.5,1
gwidth 1,1,0,1,1,0,3,3,0,3,3,0


go

tge ccntr
getn 1
go

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