G95 on Linux

Introduction | The G95 compiler | PGPLOT | Sample Fortran code

Introduction

Here I describe how I got the G95 Fortran compiler up and running on Linux (Debian testing, but should work with most vaguely sensible distributions) with the PGPLOT library (useful for drawing graphs and such).

^^ back to top

The G95 compiler

Getting it

The compiler itself can be found at the G95 project pages at Sourceforge. I opted for the Linux x86 Binary release, although sources are also available. If compiling from sources, you are advised to read the related documentation.

Unpacking and installing

Unpack the .tgz file in the usual way:

phunf@cricket:~$ tar -xzf g95-x86-linux.tgz
phunf@cricket:~$ cd g95-install/
phunf@cricket:~/g95-install$ ls
bin  INSTALL  lib
phunf@cricket:~/g95-install$

I decided to install the compiler into /usr/local (you'll need to be root to do this), although it could just as easily go in your home directory providing that ~/bin is in $PATH.

phunf@cricket:~/g95-install$ su
Password: <root password>
cricket:/home/phunf/g95-install# cp bin/* /usr/local/bin/
cricket:/home/phunf/g95-install# cp lib/* /usr/local/lib/ -R
cricket:/home/phunf/g95-install# exit
phunf@cricket:~/g95-install$

As supplied in the binary package, the compiler is called i686-pc-linux-gnu-g95. To save typing, I symlinked it to /usr/local/bin/g95:

phunf@cricket:~$ su
Password: <root password>
cricket:/home/phunf# cd /usr/local/bin
cricket:/usr/local/bin# ln -s i686-pc-linux-gnu-g95 g95
cricket:/usr/local/bin# exit
phunf@cricket:~$ g95
g95: no input files
phunf@cricket:~$

Testing

Here is hello.f90:

PROGRAM hello
  PRINT*,'Hello world'
END PROGRAM hello

Compile & run:

phunf@cricket:~$ g95 -o hello hello.f90
phunf@cricket:~$ ./hello
 Hello world
phunf@cricket:~$

As with most compilers, g95 takes a list of source files as parameters (in this case test.f90), along with any additional options (in this case, -o to specify an alternative output file).

^^ back to top

PGPLOT

Getting and unpacking

PGPLOT is a graphical library sometimes used with Fortran. It produces output in a number of formats including Postscript, JPEG and PNG, as well as directly to an X window.

Download the source code from Caltech and unpack as before:

phunf@cricket:~$ tar -xzf pgplot5.2.tar.gz
phunf@cricket:~$ cd pgplot/
phunf@cricket:~/pgplot$ ls
aaaread.me        makedoc    sys_alliant   sys_irix      sys_vms
applications      makehelp   sys_arc       sys_linux     sys_win
(... loads of other files ...)
phunf@cricket:~/pgplot$

Decide where to install PGPLOT. I chose /usr/local/pgplot but (as before) you'll need to be root to install it here. Create the installation directory:

phunf@cricket:~/pgplot$ su
Password: <root password>
cricket:/home/phunf/pgplot# mkdir /usr/local/pgplot
cricket:/home/phunf/pgplot# chown phunf.users /usr/local/pgplot
cricket:/home/phunf/pgplot# exit
phunf@cricket:~/pgplot$

I also changed the ownership of the installation directory, to perform the rest of the installation as a non-root user.

Configuring and compiling

Before compilation, we need to decide which output formats/drivers we want to use with PGPLOT. Copy drivers.list from the PGPLOT source directory into the installation directory and open in your favourite text editor:

phunf@cricket:~/pgplot$ cp drivers.list /usr/local/pgplot/
phunf@cricket:~/pgplot$

The default output is NULL (no output). I added XWINDOW, XSERVE (both of which allow output to an X window) and PS (Postscript) by removing the exclamation mark from the beginning of the appropriate lines.

Next, we hit problems. PGPLOT doesn't have support for our compiler as standard, so we need to create a new configuration file for our setup. Thankfully this isn't too hard - we can just copy an existing one and change it a bit; I based mine on the NAGWare f95 file.

phunf@cricket:~/pgplot$ cd sys_linux
phunf@cricket:~/pgplot/sys_linux$ cp f95_gcc.conf \
  /usr/local/pgplot/local.conf
phunf@cricket:~/pgplot/sys_linux$

The changes I made were:

Changing FCOMPL to use g95
Changing FFLAGC to "-Wall,-fPIC -O"
Changing FFLAGD to "-Wall"
Commented out (with a #) the SYSDIR line

Create a Makefile using the makemake utility supplied with PGPLOT.

phunf@cricket:~/pgplot$ cd /usr/local/pgplot/
phunf@cricket:/usr/local/pgplot$ ~/pgplot/makemake ~/pgplot linux
For additional information, read file /home/phunf/pgplot/
  sys_linux/aaaread.me
Reading configuration file: ./local.conf
Selecting uncommented drivers from ./drivers.list
Found drivers NUDRIV PSDRIV XWDRIV
Copying color database.
Creating make file: makefile
Determining object file dependencies.
phunf@cricket:/usr/local/pgplot$

The moment of truth: type make at a shell prompt to set it going...

Testing PGPLOT

With a bit of luck, after a few minutes you'll get a message looking like this:

*** Finished compilation of PGPLOT ***

Note that if you plan to install PGPLOT in a different
directory than the current one, the following files will be
needed.

       libpgplot.a
       libpgplot.so
       grfont.dat
       rgb.txt
       pgxwin_server

Also note that subsequent usage of PGPLOT programs requires that
the full path of the chosen installation directory be named in
an environment variable named PGPLOT_DIR.

phunf@cricket:/usr/local/pgplot$

Before reaching for the demos supplied with PGPLOT, you'll need to tell the dynamic linker where libpgplot.so is - this contains the compiled PGPLOT code. There are at least two ways of doing this:

add /usr/local/pgplot to /etc/ld.so.conf and run ldconfig as root
set the environment variable $LD_LIBRARY_PATH before running any programs which make use of PGPLOT

Additionally (as the message helpfully points out) the PGPLOT_DIR variable should be set, so PGPLOT can find its fonts and helper programs. With all this in mind, you can try one of the demos by typing (in /usr/local/pgplot):

LD_LIBRARY_PATH=/usr/local/pgplot PGPLOT_DIR=/usr/local/pgplot \
  ./pgdemo1

PGPLOT should respond with:

Graphics device/type (? to see list, default /NULL):

Typing ? gives the list:

 PGPLOT v5.2.2 Copyright 1997 California Institute of Technology
 Interactive devices:
    /XWINDOW   (X window window@node:display.screen/xw)
    /XSERVE    (A /XWINDOW window that persists for re-use)
 Non-interactive file formats:
    /NULL      (Null device, no output)
    /PS        (PostScript file, landscape orientation)
 Graphics device/type (? to see list, default /NULL):

Pick /XWINDOW and you should be presented with a tasteful plot of y=x². By repeatedly hitting ENTER in the terminal window, the demo cycles through a range of graphs, functions and shapes.

The other demo programs appear to test various aspects of PGPLOT as follows:

pgdemo2 - fonts, line widths, clipping, something involving ducks
pgdemo3 - contouring
pgdemo4 - some colour mapping thing with broken keyboard controls
pgdemo5 - draw polygons with the mouse (providing you don't select something stupid like Postscript as an output device)
pgdemo6 - draw little markers on a set of axes and find out their position; press + a few times for some crosshairs
pgdemo7 - draws a 3D function
pgdemo8 - draws a red and blue thing
pgdemo9 - draws a rather cool purple contour map
pgdemo10 - colours
pgdemo11 - two different methods of "animation"
pgdemo12 - resizing the display
pgdemo13 - multiple devices, driven by a graphical menu
pgdemo14 - editable fields
pgdemo15 - drawing vector fields
pgdemo16 - bar charts
pgdemo17 - 3D rotation

Tidying up

You can remove the .o files in the installation directory - they're only used during compilation.

phunf@cricket:/usr/local/pgplot$ rm *.o
phunf@cricket:/usr/local/pgplot$

^^ back to top

Sample Fortran code

graph.f90:

PROGRAM graph
  IMPLICIT NONE
  INTEGER :: i, ier, pgbeg
  REAL, DIMENSION(6) :: Xpoints, Ypoints
  
  ier=pgbeg(0, '?', 1, 1)
  IF (ier/=1) STOP
  CALL pgenv(0.0, 1.0, 0.0, 1.0, 0, 1)
  CALL pglab('X', 'Y', 'Graph of nothing in particular')

  DO i=0, 5, 1
    IF (i/=0) THEN
      Xpoints(i+1)=i/5.0
      Ypoints(i+1)=(i*i)/25.0
    ELSE
      Xpoints(i+1)=0.0
      Ypoints(i+1)=0.0
    END IF
    PRINT*,i,Xpoints(i+1),Ypoints(i+1)
  END DO
  
  CALL pgline(SIZE(Xpoints, 1), Xpoints, Ypoints)
  CALL pgend
END PROGRAM graph

To compile:

g95 -o graph graph.f90 -L/usr/X11R6/lib -L/usr/local/pgplot -lX11 \
    -lpgplot

Note how we link with the PGPLOT and X11 libraries. Then to run:

LD_LIBRARY_PATH=/usr/local/pgplot PGPLOT_DIR=/usr/local/pgplot \
  ./graph

Tada. Let me know if you encounter any problems during compiling/installing, and I'll try to update this page with any common issues and their solutions.

^^ back to top