dcdfort_reader Module Reference

Module that contains dcdreader class. More...

Data Types
type	dcdfile
	dcdwriter class More...

Functions/Subroutines
subroutine	dcdfile_open (this, filename)
	Opens file to read from. More...
subroutine	dcdfile_read_header (this, nframes, istart, nevery, iend, timestep, natoms)
	Reads header of open DCD file. More...
subroutine	dcdfile_close (this)
	Closes DCD file. More...
subroutine	dcdfile_read_next (this, xyz, box)
	Reads next frame into memory. More...
subroutine	dcdfile_skip_next (this, n)
	Skips reading this frame into memory. More...

Detailed Description

Module that contains dcdreader class.

Function/Subroutine Documentation

dcdfile_close()

subroutine dcdfort_reader::dcdfile_close ( class(dcdfile), intent(inout)  this )

private

Closes DCD file.

Parameters

[in,out]

this

dcdreader object

        implicit none
        class(dcdfile), intent(inout) :: this

        close(this%u)

dcdfile_open()

subroutine dcdfort_reader::dcdfile_open	(	class(dcdfile), intent(inout)	this,
		character(len=*), intent(in)	filename
	)

Opens file to read from.

Also detects if the DCD file is compatible with this library and swaps endinness if necessary.

Parameters

[in,out]	this	dcdreader object
[in]	filename	name of of DCD file to read from

        implicit none
        character(len=*), parameter :: magic_string = "CORD"
        integer(int32), parameter :: magic_number = 84
        character(len=*), intent(in) :: filename
        class(dcdfile), intent(inout) :: this
        integer(kind=int32) :: line1, charmm_version, has_extra_block, four_dimensions
        character(len=4) :: line2
        logical :: ex

        ! Does file exist?
        inquire(file=trim(filename), exist=ex, size=this%filesize)
        if (ex .eqv. .false.) then
            call error_stop_program("The specified DCD file '"//trim(filename)//"' does not exist.")
        end if

        ! Open file in native endinness
        open(newunit=this%u, file=trim(filename), form="unformatted", access="stream", status="old")

        ! Read in magic number of magic string
        read(this%u,pos=1) line1
        read(this%u) line2

        ! Ensure the magic number and string are correct, if not we'll swap the endinness
        if (line1 .ne. magic_number .or. line2 .ne. magic_string) then

            ! Try converting to the reverse endianness
            close(this%u)
            open(newunit=this%u, file=trim(filename), form="unformatted", access="stream", status="old", convert="swap")

            read(this%u,pos=1) line2
            read(this%u) line2

            ! We tried both native and reverse endiness and didn't have magic number or string
            if (line1 .ne. magic_number .or. line2 .ne. magic_string) then
                call error_stop_program("This DCD file format is not supported, or the file header is corrupt.")
            end if

        end if

        ! Check if the file identifies as CHARMM (LAMMPS pretends to be CHARMM v. 24)
        read(this%u, pos=85) charmm_version
        if (charmm_version .eq. 0) then
            call error_stop_program("DCD file indicates it is not CHARMM. Only CHARMM-style DCD files are supported.")
        end if

        ! We only support files with the extra unitcell block
        read(this%u, pos=49) has_extra_block
        if (has_extra_block .ne. 1) then
            call error_stop_program("DCD file indicates it does not have unit cell information. Only DCD files with&
                & unit cell information are supported.")
        end if

        ! We don't support files with four dimensions
        read(this%u) four_dimensions
        if (four_dimensions .eq. 1) then
            call error_stop_program("DCD file indicates it has four dimensions. Only DCD files with three dimensions&
                & are supported.")
        end if

dcdfile_read_header()

subroutine dcdfort_reader::dcdfile_read_header ( class(dcdfile), intent(inout)  this, integer(kind=int32), intent(out)  nframes, integer(kind=int32), intent(out)  istart, integer(kind=int32), intent(out)  nevery, integer(kind=int32), intent(out)  iend, real(kind=real32), intent(out)  timestep, integer(kind=int32), intent(out)  natoms  )

private

Reads header of open DCD file.

Should be called after open()

Parameters

[in,out]	this	dcdreader object
[in]	nframes	rnumber of frames (snapshots) in file
[out]	istart	first timestep of trajectory file
[out]	nevery	how often (in timesteps) file was written to
[out]	iend	last timestep of trajectory file
[out]	timestep	timestep of simulation
[out]	natoms	number of atoms in each snapshot

        implicit none

        integer(kind=int32), intent(out) :: nframes, istart, nevery, iend, natoms
        integer(kind=int32) :: i, ntitle, n, dummy, pos
        integer(kind=int64) :: nframes2
        character(len=80) :: title_string
        real(kind=real32), intent(out) :: timestep
        class(dcdfile), intent(inout) :: this

        read(this%u, pos=9) nframes, istart, nevery, iend

        read(this%u, pos=45) timestep

        read(this%u, pos=97) ntitle
        if (ntitle > 0) then
            write(error_unit,'(a)') prompt//"The following titles were found:"
        end if
        do i = 1, ntitle
            read(this%u) title_string

            n = 1
            do while (n .le. 80 .and. title_string(n:n) .ne. c_null_char)
                n = n + 1
            end do

            write(error_unit,'(a)') prompt//"  "//trim(title_string(1:n-1))
        end do

        read(this%u) dummy, dummy
        if (dummy .ne. 4) then
            call error_stop_program("This DCD file format is not supported, or the file header is corrupt.")
        end if

        ! Number of atoms in each snapshot
        read(this%u) natoms, dummy
        if (dummy .ne. 4) then
            call error_stop_program("This DCD file format is not supported, or the file header is corrupt.")
        end if

        inquire(unit=this%u, pos=pos)
        pos = pos - 1

        ! Each frame has natoms*3 (4 bytes each) = natoms*12
        ! plus 6 box dimensions (8 bytes each) = 48
        ! Additionally there are 32 bytes of file information in each frame
        this%framesize = natoms*12 + 80
        ! Header is typically 276 bytes, but inquire gives us exact size
        nframes2 = (this%filesize-pos)/this%framesize
        if ( nframes2 .ne. nframes) then
            write(error_unit,'(a,i0,a,i0,a)') prompt//"WARNING: Header indicates ", nframes, &
                &" frames, but file size indicates ", nframes2, "." 
            nframes = int(nframes2)
        end if

dcdfile_read_next()

subroutine dcdfort_reader::dcdfile_read_next ( class(dcdfile), intent(inout)  this, real(kind=real32), dimension(:,:), intent(inout), allocatable  xyz, real(kind=real64), dimension(6), intent(inout)  box  )

private

Reads next frame into memory.

Parameters

[in,out]	this	dcdreader object
[in,out]	xyz	coordinates of all atoms in snapshot. First dimension is atom number, second dimension is x, y, or z !coordinate.
[in,out]	box	dimensions of snapshot. Array containing 6 elements, ordered as A, B, C, alpha, beta, gamma. A = length of unit cell vector along x-axis; B = length of unit cell vector in xy-plane; C = length of unit cell vector in yz-plane; alpha = cosine of angle between B and C; beta = cosine of angle between A and C; gamma = cosine of angle between A and B;

        implicit none
        real(kind=real32), allocatable, intent(inout) :: xyz(:,:)
        real(kind=real64), intent(inout) :: box(6)
        integer(kind=int32) :: dummy(6), nbytes, ndims, i
        class(dcdfile), intent(inout) :: this

        nbytes = size(xyz,1)*4
        ndims = size(xyz,2)

        if (ndims /= 3) then
            call error_stop_program("Number of dimensions of xyz array is incorrect.")
        end if
    
        read(this%u) dummy(1)
        if (dummy(1) /= 48) then
            call error_stop_program("Problem reading in DCD snapshot.")
        end if

        !            A       gamma   B       beta    alpha   C
        read(this%u) box(1), box(6), box(2), box(5), box(4), box(3)
        if (box(1) < 0 .or. box(2) < 0 .or. box(3) < 0) then
            call error_stop_program("Problem reading in DCD snapshot box dimensions.")
        end if

        ! 48, then no. of bytes for x coordinates, x coordinates (repeat for y and z coordinates)
        read(this%u) dummy(1:2), xyz(:,1), dummy(3:4), xyz(:,2), dummy(5:6), xyz(:,3)

        if (dummy(1) /= 48) then
            call error_stop_program("Problem reading in DCD snapshot coordinates.")
        end if

        do i = 2, 6
            if (dummy(i) /= nbytes) then
                call error_stop_program("Number of bytes in DCD snapshot is incorrect for size of xyz array passed.")
            end if
        end do

        read(this%u) dummy(1)
        if (dummy(1) .ne. nbytes) then
            call error_stop_program("Problem reading in DCD snapshot.")
        end if

dcdfile_skip_next()

subroutine dcdfort_reader::dcdfile_skip_next ( class(dcdfile), intent(inout)  this, integer(kind=int32), intent(in), optional  n  )

private

Skips reading this frame into memory.

Parameters

[in,out]	this	dcdreader object
[in]	n	number of frames to skip

        implicit none
        integer(kind=int32) :: dummy
        integer(kind=int64) :: pos, newpos
        integer(kind=int32), intent(in), optional :: n
        class(dcdfile), intent(inout) :: this
   
        ! Where are we?
        inquire(unit=this%u, pos=pos)

        ! We subtract 4 bytes so that the next read of the 4-byte integer will line things up properly for the next read
        if (.not. present(n)) then
            newpos = pos + this%framesize - 4
        else
            newpos = pos + this%framesize*n - 4
        end if
        
        read(this%u, pos=newpos) dummy