[ncl-talk] A NCL Mystery Solved

Thu Oct 19 09:55:17 MDT 2017

Hi:

The "problem" was the mystery, or confusion.

The original code I wrote was much longer (and has non zeros), but the
excerpt produces the error when the colon (:) is included.

I was wondering why including the : caused an error when I defined the left
hand side variable beforehand as an array, but did not when it was just set
it equal to 0, for example, without defining it as an array.

I have used the colon before when doing calculations in other programs, but
must not have done so when defining variables as an array beforehand.

Had I written hits_1 := hits_12km

without any array subscripting it would have worked.

But when I include array subscripting the colon causes a redefinition that
gave that error I didn't find in google.

Just to reiterate, I was asking why, and I believe that the both of you
answered why within this e-mail chain.

Thanks for clarifying.

Barry

On Thu, Oct 19, 2017 at 6:18 PM, Marston Johnston <shejo284 at gmail.com>
wrote:

> Good points Alan.
>
>
>
> I tried to make some of this clear to Barry offline. But you are more
> “eloquent”.
>
> We do need to see the problem - agreed.
>
>
>
> /M
>
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Marston S. Ward, PhD
>
> Department of Earth Sciences
>
> University of Gothenburg, Sweden
>
> Email: marston.johnston at gu.se
>
> SkypeID: marston.johnston
>
> Phone: +46-31-7864901 <+46%2031%20786%2049%2001>
>
> Only the fruitful thing is true!
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
>
>
> *From: *ncl-talk <ncl-talk-bounces at ucar.edu> on behalf of Alan Brammer <
> abrammer at albany.edu>
> *Date: *Thursday, 19 October 2017 at 17:16
> *To: *Barry Lynn <barry.h.lynn at gmail.com>
> *Cc: *ncl-talk <ncl-talk at ucar.edu>
> *Subject: *Re: [ncl-talk] A NCL Mystery Solved
>
>
>
> := effectively deletes the variable on the left hand side (if it exists)
> then points to the right hand side to the newly defined variable.
> Therefore you can't use indexing and := as the left hand side variable no
> longer exists.
>
>
>
> it would
>
> kind of 
>
> be the same as:
>
>
>
> if(isdefined("Hits_1"))
>      delete(Hits_1)
> end if
> Hits_1(i_day) = Hits_4km(i_day) + Hits_1(i_day)
>
> ;; not going to work as Hits_1 is now undefined.
>
>
>
> ;;  Right hand side will work, but left hand side will fail.
>
> You've deleted Hits_1 so there is no dimension or coordinates associated.
>
> As Marston said though, your code just add's a bunch of zeros together,
> hopefully that was just pseudocode and there is something else going on.
>
>
>
> If the right hand side is a different shape, type to the left hand side
> then you need the := operator, if you actually want to redefine the left
> hand side.   It's hard to answer why you got an error based on code we
> can't see.
>
>
>
> The := is great to easily handle redefining variables, but if you just
> throw it around everywhere then things will happen that you're not
> expecting.
>
>  Rather than blindly solving issues with the := operator, workout why you
> have the issue then decide if redefining the variable is the right answer.
>
>
>
>
>
>
>
>
>
>
>
> On Thu, Oct 19, 2017 at 11:09 AM, Barry Lynn <barry.h.lynn at gmail.com>
> wrote:
>
> and I am wondering why it is needed...
>
>
>
> On Thu, Oct 19, 2017 at 5:49 PM, Barry Lynn <barry.h.lynn at gmail.com>
> wrote:
>
> Hi:
>
>
>
> It only gives the error when the : is included after Hits_1(i_day), as in
> :=.
>
>
>
> The : was needed before I subscripted the variable with i_day.
>
>
>
> Barry
>
>
>
> On Thu, Oct 19, 2017 at 5:31 PM, Marston Johnston <shejo284 at gmail.com>
> wrote:
>
> Hi Barry,
>
>
>
> A couple things, not to be nit-picky but just my experience. I rewrote the
> script a bit. But I’m confused, your arrays are always empty so Hits_1 will
> always be 0.
>
> This version of the script doesn’t give the error:
>
>
>
> begin
>
>   n_days  = 3
>
>   dims = 9
>
>   Hits_1 = new(n_days,"float")
>
>   Hits_4km = new(n_days,"float")
>
>   Hits_1 = 0.0
>
>   Hits_4km = 0.0
>
>   do ii_day = 0,dims-1
>
>     if (ii_day .eq.0)then
>
>       i_day = 0
>
>     else
>
>       i_day = (mod(ii_day,3))
>
>     end if
>
>     ;printVarSummary(i_day)
>
>     ;print("i_day = "+ i_day)
>
>     Hits_1(i_day) = Hits_4km(i_day) + Hits_1(i_day)
>
>     print(Hits_1(i_day))
>
>   end do
>
> end
>
>
>
> /M
>
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Marston S. Ward, PhD
>
> Department of Earth Sciences
>
> University of Gothenburg, Sweden
>
> Email: marston.johnston at gu.se
>
> SkypeID: marston.johnston
>
> Phone: +46-31-7864901 <+46%2031%20786%2049%2001>
>
> Only the fruitful thing is true!
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>
>
>
> *From: *ncl-talk <ncl-talk-bounces at ucar.edu> on behalf of Barry Lynn <
> barry.h.lynn at gmail.com>
> *Date: *Thursday, 19 October 2017 at 16:18
> *To: *ncl-talk <ncl-talk at ucar.edu>
> *Subject: *[ncl-talk] A NCL Mystery Solved
>
>
>
> Hi:
>
>
>
> I have this error (it didn't obviously show up with a Google search).
>
>
>
> fatal:Assign: Hits_1 is undefined, can not subscript an undefined variable
>
> fatal:["Execute.c":8575]:Execute: Error occurred at or near line 17 in
> file ./test.ncl
>
> Before defining Hits_1 as an array of size n_days, I needed the : to do
> the sum.
>
> However, it is the : that causes the error when the variable is defined as
> an array.
>
> I am not sure why, but I thought I would make a note of it for those who
> encounter the same error message.
>
>
>
> begin
>
>   n_days  = 3
>
>   dims = 9
>
>   Hits_1 = new(n_days,float)
>
>   printVarSummary(Hits_1)
>
>   Hits_4km = new(n_days,float)
>
>   Hits_1 = 0
>
>   Hits_4km = 0
>
>   do ii_day = 0,dims,1
>
>    if (ii_day .eq.0)then
>
>    i_day = tointeger(0)
>
>    else
>
>    i_day = (mod(ii_day,3))
>
>    end if
>
>    printVarSummary(i_day)
>
>    print("i_day = " + i_day)
>
>     *Hits_1(i_day) := Hits_4km(i_day) + Hits_1(i_day) ; **remove colon if
> Hits_1 is defined as an array.*
>
>   end do
>
> end
>
>
>
>
>
> --
>
> Barry H. Lynn, Ph.D
>
> Senior Lecturer,
>
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
>
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
>
>
> C.E.O, Weather It Is, LTD
> Weather and Climate Focus
> http://weather-it-is.com
> Jerusalem, Israel
> Local: 02 930 9525
> Cell: 054 7 231 170
> Int-IS: x972 2 930 9525
> US 914 432 3108 <(914)%20432-3108>
>
> _______________________________________________ ncl-talk mailing list
> ncl-talk at ucar.edu List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>
>
>
>
>
> --
>
> Barry H. Lynn, Ph.D
>
> Senior Lecturer,
>
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
>
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
>
>
> C.E.O, Weather It Is, LTD
> Weather and Climate Focus
> http://weather-it-is.com
> Jerusalem, Israel
> Local: 02 930 9525
> Cell: 054 7 231 170
> Int-IS: x972 2 930 9525
> US 914 432 3108 <(914)%20432-3108>
>
>
>
>
>
> --
>
> Barry H. Lynn, Ph.D
>
> Senior Lecturer,
>
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
>
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
>
>
> C.E.O, Weather It Is, LTD
> Weather and Climate Focus
> http://weather-it-is.com
> Jerusalem, Israel
> Local: 02 930 9525
> Cell: 054 7 231 170
> Int-IS: x972 2 930 9525
> US 914 432 3108 <(914)%20432-3108>
>
>
> _______________________________________________
> ncl-talk mailing list
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>
>
>
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>

-- 
Barry H. Lynn, Ph.D
Senior Lecturer,
The Institute of the Earth Science,
The Hebrew University of Jerusalem,
Givat Ram, Jerusalem 91904, Israel
Tel: 972 547 231 170
Fax: (972)-25662581

C.E.O, Weather It Is, LTD
Weather and Climate Focus
http://weather-it-is.com
Jerusalem, Israel
Local: 02 930 9525
Cell: 054 7 231 170
Int-IS: x972 2 930 9525
US 914 432 3108
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