# [ncl-talk] Division problem

Md. Jalal Uddin dmjalal90 at gmail.com
Fri Jan 25 20:43:50 MST 2019

```Thanks a lot. It works now.

On Sat, Jan 26, 2019 at 2:50 AM Dennis Shea <shea at ucar.edu> wrote:

> Toni's answer is correct.
>
> You could also searh the NCAR archives for (say) "division by zero"
> ===
> See the "caveat" section of the following:
>
> *http://www.ncl.ucar.edu/Document/Functions/Built-in/where.shtml*
> <http://www.ncl.ucar.edu/Document/Functions/Built-in/where.shtml>
>
>  y = ispan (-5,5,1)*1.0
>  y at _FillValue = -999.0
>  print(y)
>  z = 1.0/*where*(y.ne.0, y, y at _FillValue)     ; or, equivalently:  *where*(y.eq.0.0,
> y at _FillValue, y)
>  print(y+"   "+z)
>
> ===
> (0)     -5   -0.2
> (1)     -4   -0.25
> (2)     -3   -0.333333
> (3)     -2   -0.5
> (4)     -1   -1
> *(5)     0   -999*
> (6)     1   1
> (7)     2   0.5
> (8)     3   0.333333
> (9)     4   0.25
> (10)    5   0.2
>
> On Fri, Jan 25, 2019 at 6:47 AM Toni Klemm <toni-klemm at tamu.edu> wrote:
>
>> Hi Jalal,
>>
>> Are you dividing the average January rainfall by the rainfall of a single
>> year to see how it compares? That’s how I understand your code.
>>
>> Then the problem might be that your individual year has zero rainfall in
>> January, thus division by zero. I had a similar problem. Try to check if
>> your data (jannontc) is zero, and replace zeros with missing values. That
>> way NCL won’t divide. You might get a warning message but it should be
>> okay.
>>
>> For example:
>> if (jannontc .eq. 0) then
>>   jannontc = prc at _FillValue
>> end if
>>
>> I hope that helps.
>>
>> Best,
>> Toni
>>
>>
>> *Toni Klemm**, Ph.D.*
>> Postdoctoral Research Associate
>> Department of Ecosystem Science and Management
>> College of Agriculture and Life Sciences
>> Texas A&M University, College Station, TX
>> Contributor to the Early Career Climate Forum <https://www.eccforum.org/>
>> www.toni-klemm.de | @toniklemm <https://twitter.com/ToniKlemm>
>>
>>
>> On Jan 25, 2019, at 7:13 AM, Md. Jalal Uddin <dmjalal90 at gmail.com> wrote:
>>
>> Hi all,
>>
>> I can minus and multiply but cannot divide. NCL says, "divide by 0 cannot
>> continue". Any suggestions?
>>
>> ;January
>>  f  = addfile("all_jan.nc
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__all-5Fjan.nc&d=DwMFaQ&c=ODFT-G5SujMiGrKuoJJjVg&r=WsLJ5ywbW3XnTzqo_ETV62H6s1a5bcGgnrpl7xPRfic&m=2oVRg1Gv-7_n71W5tmt0snEIqLy6wzfrkfrTQ0nH_Vk&s=S9iFutzrm_V25uuLNsGJYLacYQwyt9Ht_JJjd2FoH6I&e=>",
>> "r")
>>  prc =f->pre(:,{65:110},{0:30})
>>  prc_reorder = prc(time|:,latitude|:,longitude|:)
>>
>> ; January TCs average rainfall
>>  ntim = (/12,13,14,15,16,34,35,36,37/)
>>  tcjan = prc_reorder(ntim,:,:)
>>  tcavgjan = dim_avg_n_Wrap(tcjan,0)
>>
>> ; January contribution
>> totjan = dim_sum_n_Wrap(prc_reorder,0)
>> jantc = dim_sum_n_Wrap(tcjan,0)
>> jannontc = totjan - jantc
>> copy_VarMeta(totjan,jannontc)
>>
>> jancont = jantc / jannontc    ; problem from there
>> copy_VarMeta(jantc,jancont)
>>
>> --
>> *Md. Jalal Uddin*
>> MSc in Applied Meteorology (English Language)
>> Nanjing University of Information, Science and Technology, China
>> B.Sc. in Disaster Management (Hons.)
>> Patuakhali Science and Technology University, Bangladesh.
>> Cell: +8613260859092, +8801792052662
>> Web: www.dmjalal90.weebly.com
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.dmjalal90.weebly.com&d=DwMFaQ&c=ODFT-G5SujMiGrKuoJJjVg&r=WsLJ5ywbW3XnTzqo_ETV62H6s1a5bcGgnrpl7xPRfic&m=2oVRg1Gv-7_n71W5tmt0snEIqLy6wzfrkfrTQ0nH_Vk&s=ylrSG_BqgtyXgC0wxp3ioTsRRaPUCvFlmg6emXFy0Jc&e=>
>>
>>
>> Skype: dmjalal90
>>
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>

--
*Md. Jalal Uddin*
MSc in Applied Meteorology (English Language)
Nanjing University of Information, Science and Technology, China
B.Sc. in Disaster Management (Hons.)
Patuakhali Science and Technology University, Bangladesh.
Cell: +8613260859092, +8801792052662
Web: www.dmjalal90.weebly.com