[ncl-talk] Floating point issue

[Graziela Luzia]

Hello ncl-users.

I'm converting a csv file in netcdf and apparently my script, although not
very efficient (I'm a begginer) was working fine. But for some points it
dindn't write correctly. I've checked everything and I supose the problem
is converting string to float, but I can't figure out how can I solve this
problem.

I don't understand why it shows me a value like 42.6 but it is like it was
42.600002. It causes me trouble when I compare it with another variable
equal to 42.6, it returns a false result. Also, it only happen to some
values, like 42.6 (but not with 50.2) as you can see below.

I've tried to use decimalPlaces, but it results the same.
I'd apreciate any information. Thanks in advance.

uname-a: Linux Tower2 4.15.0-45-generic #48~16.04.1-Ubuntu SMP Tue Jan 29
18:03:48 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Graziela.

---
lines = asciiread("resultado.csv",-1,"string")
data = lines(1:) ; exclude line 0 header

;xlon = decimalPlaces(tofloat(str_get_field(data,1,",")),1,True)
xlon=tofloat(str_get_field(data,1,","))

xlon1 = new(600,"float",-999)
   do i=0,599
      xlon1(i)=xlon(i*8)+0.1
   end do

print(xlon1(0:29))

a=xlon1(23)-xlon1(24)
print(a)

b=ind(xlon1(0:29).eq.-50.2)
c=ind(xlon1(0:29).eq.-42.6)
print(b)
print(c)

----
labren at Tower2:~/Documentos/Produto3$ ncl teste.ncl
 Copyright (C) 1995-2015 - All Rights Reserved
 University Corporation for Atmospheric Research
 NCAR Command Language Version 6.3.0
 The use of this software is governed by a License Agreement.
 See http://www.ncl.ucar.edu/ for more details.

Variable: xlon1 (subsection)
Type: float
Total Size: 120 bytes
            30 values
Number of Dimensions: 1
Dimensions and sizes: [30]
Coordinates:
Number Of Attributes: 1
  _FillValue : -999
(0) -50.2
(1) -50.2
(2) -50.2
(3) -50.2
(4) -50.2
(5) -50.2
(6) -50.2
(7) -50.2
(8) -50.2
(9) -50.2
(10) -50.2
(11) -50.2
(12) -50.2
(13) -50.2
(14) -50.2
(15) -50.2
(16) -50.2
(17) -50.2
(18) -50.2
(19) -50.2
(20) -50.2
(21) -50.2
(22) -50.2
(23) -50.2
(24) -42.6
(25) -42.6
(26) -42.6
(27) -42.6
(28) -42.6
(29) -42.6

Variable: a
Type: float
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
Number Of Attributes: 1
  _FillValue : -999
(0) -7.599998


Variable: b
Type: integer
Total Size: 96 bytes
            24 values
Number of Dimensions: 1
Dimensions and sizes: [24]
Coordinates:
(0) 0
(1) 1
(2) 2
(3) 3
(4) 4
(5) 5
(6) 6
(7) 7
(8) 8
(9) 9
(10) 10
(11) 11
(12) 12
(13) 13
(14) 14
(15) 15
(16) 16
(17) 17
(18) 18
(19) 19
(20) 20
(21) 21
(22) 22
(23) 23

Variable: c
Type: integer
Total Size: 4 bytes
            1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
Number Of Attributes: 1
  _FillValue : -2147483647
(0) -2147483647

My csv file contain values like this:

xlon,ylat,ano,mes,direcao,v1,v2,v3,v4
-50.3,-30.4,2016,1,45,0,0.0020206556,0.0017961383
-50.3,-30.4,2016,1,90,0.0002245173,0.0004490346,0.0049393803,0.0246969017
-50.3,-30.4,2016,1,135,0.0011225864,0.0029187247,0.0114503817,0.0177368657
-50.3,-30.4,2016,1,180,0,0.0017961383,0.0038167939,0.0141445891 (...)
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