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Emanuele
Joined: 21 Oct 2009
Posts: 78
Location: Bologna (Italy)
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 Posted: Wed Nov 16, 2011 8:04 pm Post subject: Reading double precision numbers |
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When reading floating point numbers from a text file, I get slight numeric differences between Win32 and NET configuration.
Please, consider the following piece of code:
| Code: |
program Test
character(len=10):: a
double precision:: x, y, z
integer:: k
open(unit=10,file='Input.txt',status='old')
read(10,*)a,x,y,z,k
close(10)
open(unit=20,file='Output.txt',status='replace')
write(20,100) a,k,x,y,z
close(20)
100 format(a10,3x,i1,/,3(f24.14,5x))
end
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Let the file 'Input.txt' contain the following text:
| Quote: |
PT128R7 4321.12 654321.12 21.1 9
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When compiled in Win32 mode the 'Output.txt' looks like this:
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PT128R7 9
4321.11999999999990 654321.11999999999539 21.10000000000000
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As you can see a slight numeric difference appears.
Instead, when compiled in NET mode, the output is perfect:
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PT128R7 9
4321.12000000000000 654321.12000000000000 21.10000000000000
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I am using FTN95 6.00 and Plato under Windows 7 Pro 64 bit.
Can someone explain this effect? |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8254
Location: Salford, UK
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| Posted: Wed Nov 16, 2011 8:19 pm Post subject: |
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With double precision you only get about 15 significant figures.
When you round off, the results are the same. |
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Emanuele
Joined: 21 Oct 2009
Posts: 78
Location: Bologna (Italy)
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| Posted: Wed Nov 16, 2011 9:29 pm Post subject: |
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| Yes, you are right. I'd just like to understand the different behaviour of the two configurations... |
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PaulLaidler
Site Admin
Joined: 21 Feb 2005
Posts: 8254
Location: Salford, UK
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| Posted: Thu Nov 17, 2011 8:52 am Post subject: |
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| The answer will probably be deep down within the FTN95 input/output library. |
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