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Write array to X,Y formatted file

 
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arctica



Joined: 10 Sep 2006
Posts: 71
Location: United Kingdom

PostPosted: Thu Jun 04, 2020 10:17 am    Post subject: Write array to X,Y formatted file Reply with quote

Hello,

I am trying to write X,Y values to a file from a 2D array, but the data does not output correctly in 2 columns for X and Y. At present in writes X as 2 columns and then Y appended on the end. How to write X to col 1 and Y to col 2. Sorry if this is a basic query - using ftn95.

Code:

program linear_test

! Purpose: create X and Y 2D arrays
! write file with 2 columns X,Y of 120x120 (14400) values
! z-data has same geometry
implicit none

real :: dxy, xmin, xmax, xrange, ymin, ymax, yrange
integer :: npoints, i, sv, nx, ny, xydim
real,allocatable :: xx(:), yy(:)
real, allocatable :: X(:,:), Y(:,:)

open (25, file='xy-data.dat', status='new') ! open new file for write
npoints=120

allocate(xx(npoints))
xmin = -5.0
xmax = -3.0
allocate(yy(npoints))
ymin = -5.0
ymax = -3.0

xrange = xmax - xmin
!yrange = ymax - ymin
! Linspace
dxy = xrange / real(npoints-1) ! calculate increment

    do i = 1,npoints
       xx(i) = xmin + (i-1)*dxy
       yy(i) = ymin + (i-1)*dxy !same increment in y
    end do
   
sv=0
nx = size(xx, dim=1)
ny = size(yy, dim=1)
xydim = nx*ny
allocate(X(ny,nx),Y(ny,nx),stat=sv)
allocate(X1(xydim),Y1(xydim),stat=sv)

! Meshgrid
X(1,:) = xx
X(2:ny,:) = spread(xx, dim=1, ncopies=ny-1)
Y(:,1) = yy
Y(:,2:nx) = spread(yy, dim=2, ncopies=nx-1)

! write 2 columns (X,Y)
write (25,'(f15.10,f15.10)') X, Y

deallocate(xx,yy,X,Y)
close(25)
end program linear_test


The code is fine if I just want X or Y and generates the 14400 values expected.

Thanks for any pointers

Lester
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mecej4



Joined: 31 Oct 2006
Posts: 1334

PostPosted: Thu Jun 04, 2020 10:33 am    Post subject: Reply with quote

The IOlist in the WRITE statement that you wrote is not suitable for your desired output. Instead, use

Code:
write (25,'(f15.10,f15.10)') (X(i), Y(i), i=1, npoints)
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arctica



Joined: 10 Sep 2006
Posts: 71
Location: United Kingdom

PostPosted: Thu Jun 04, 2020 11:02 am    Post subject: Re: Reply with quote

Many thanks for the pointers. The X and Y are 2D arrays so just had to tweak the line:

Code:
write (25,'(f15.10,f15.10)') (X(i,:), Y(:,i), i=1, npoints)


Currently re-learning Fortran 95; been a while!

mecej4 wrote:
The IOlist in the WRITE statement that you wrote is not suitable for your desired output. Instead, use

Code:
write (25,'(f15.10,f15.10)') (X(i), Y(i), i=1, npoints)
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mecej4



Joined: 31 Oct 2006
Posts: 1334

PostPosted: Thu Jun 04, 2020 11:20 am    Post subject: Reply with quote

Right, I overlooked the fact that you had X as well as XX as variables (also Y and YY).

Your modified WRITE statement will still print:
    nx elements of X(1,:), two per line,
    ny values of Y(:,1), two per line,

and repeats this pattern for i = 2:npoints. This may not be what you wanted.
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2184
Location: Sydney

PostPosted: Wed Jun 10, 2020 8:59 am    Post subject: Reply with quote

"write (25,'(f15.10,f15.10)') X, Y"

This is equivalent to:
write (25,'(f15.10,f15.10)') (X(i,j),i=1,ny,j=1,nx), (Y(i,j),i=1,ny,j=1,nx)

If you don't like it then re-order the implied do in the write. I presume you wanted:
write (25,'(f15.10,f15.10)') ( X(i,j),Y(i,j), i=1,ny, j=1,nx)

I find an explicit do is more flexible.
Not a very readable list though. Perhaps the following would be more useful.
write (25,'(2i5,2f15.10)') ( i,j,X(i,j),Y(i,j), i=1,ny, j=1,nx)

For Meshgrid, you could write:
Code:
do i = 1,nx
  X(:,i) = xx(i)
  Y(:,i) = yy(:)
end do
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John-Silver



Joined: 30 Jul 2013
Posts: 1380
Location: Aerospace Valley

PostPosted: Sat Jun 13, 2020 7:07 pm    Post subject: Reply with quote

John C, these are useful tips to show the variety of write format orgnisations that are possible.

I'm surprisd that:

write (25,'(f15.10,f15.10)') ( X(i,j),Y(i,j), i=1,ny, j=1,nx)

as my (ill-)logical brain would expect that the standards committee would have decided on :

Quote:
write (25,'(f15.10,f15.10)') ( ( X(i,j),Y(i,j) ) , i=1,ny, j=1,nx)


but I'm sure they have their reasoning for their sometimes counter-intuitivedecisions.

It might be difficult to prove that statement these days as F95 is now 5-30years old and many involved in the decisions made then might no longer be with us.

I saw the other day that Fortran 2018 is now the 'flavour of the day' (for want of a better expression) although it's apparently a minor update of Fortran 2008.

Maybe they're struggling to justify their existence in terms of their relevance, bearing in minf that Fortran (90/)95 does everything any engineer/scientific bod might conceivably need.

Even Fortran 77 satisfies the vast majority of Fortraneers, especially those of Anglo-Romanic descent Wink
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2184
Location: Sydney

PostPosted: Mon Jun 15, 2020 2:52 pm    Post subject: Re: Reply with quote

John-Silver wrote:
Even Fortran 77 satisfies the vast majority of Fortraneers, especially those of Anglo-Romanic descent ;-)

Don't think many would agree with that. No Allocate! or System_Clock and lots of others.

Yes, I was wrong with my brackets !!
It should be: write (25,'(f15.10,f15.10)') ( ( X(i,j),Y(i,j), i=1,ny ), j=1,nx )

"write (25,'(f15.10,f15.10)') ( ( X(i,j),Y(i,j) ) , i=1,ny, j=1,nx)" is no go either.
It could become write (25,'(f15.10,f15.10)') ( ( X(i,j) ) , i=1,ny, j=1,nx)
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mecej4



Joined: 31 Oct 2006
Posts: 1334

PostPosted: Thu Jun 25, 2020 4:00 pm    Post subject: Reply with quote

John S., you wrote
Quote:
write (25,'(f15.10,f15.10)') ( ( X(i,j),Y(i,j) ) , i=1,ny, j=1,nx)


The extra pair of parentheses is a no-no because within those parentheses are present two expressions with a comma in between. The expression (E1,E2), where E1 and E2 are constants of numeric type, is a complex constant. When E1 or E2 is not a literal constant, CMPLX(E1,E2) would give you a complex valued expression. Without CMPLX, what does (E1, E2) mean? In Fortran the integrity of parentheses in expressions has to be guarded, so the parentheses must have a purpose, but what the dickens is it? What would the following mean:
Code:
write (25,'(f15.10,f15.10)') ( ( X(i,j),Y(i,j), Z(i,j) ) , i=1,ny, j=1,nx)


Apart from the issue of extra parentheses, what about the implied DO loops? Is the i-loop inside the j-loop, or the other way?

You also wrote:

Quote:
but I'm sure they have their reasoning for their sometimes counter-intuitive decisions


Relying on intuition or Anglo-Romanic descent to resolve this question in this narrow context is almost certain to create huge problems in other parts of the language. Most of us are not far-sighted enough to see through the ramifications of changing the language just to mollify an itch of the moment.
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John-Silver



Joined: 30 Jul 2013
Posts: 1380
Location: Aerospace Valley

PostPosted: Fri Jun 26, 2020 5:23 pm    Post subject: Reply with quote

John C and mecej4, anglo-romanic was a feinted reference to our one and only LitusSaxonicum !!!!!!! ... .who for good lmeasure has coincidentally provided some of the proof of the pudding of my statement in an earlier post today http://forums.silverfrost.com/viewtopic.php?p=29398#29398

As for the brackets, mecej4, JohnC had already corrected mine as well as his drop-offs, we both had left little polly Nomial at the mercy of the dastardly Curly Pi ( https://wwwth.mpp.mpg.de/members/hahn/humour/PollyNomial.html )
_________________
''Computers (HAL and MARVIN excepted) are incredibly rigid. They question nothing. Especially input data.Human beings are incredibly trusting of computers and don't check input data. Together cocking up even the simplest calculation ... Smile "
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