[ncl-talk] A NCL Mystery Solved

Thu Oct 19 09:18:26 MDT 2017

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 

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 

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

_______________________________________________ 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

-- 

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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