Nugroho's blog.

Wednesday, November 19, 2008

First on Fortran

My first program written in fortran is below

!================================================
PROGRAM Grafik

IMPLICIT NONE
!declare variable
REAL :: gaya,ygaya,k,ky,a,ay,m,v,vy,t,x,y,z
REAL :: sbx,sby,sbz,g,fx,fy,fz
REAL :: r,dt,dx,dy,dz,dv,dvy,theta,phi
INTEGER :: i,j,n
!initial value
r =100
g =10
n =10000
k =10000
ky =1000
t=0
dt=0.001
!dx=0.01
m=10
v=0
x=10
y=10
vy=0
!create new file named data.dat (you may change the extension. I used that as I think .dat is cool extension )
OPEN (80, FILE = 'data.dat', STATUS = 'NEW', FORM = 'FORMATTED')
WRITE(80,*) ' i t x y'
CLOSE(80)

OPEN(80, ACCESS = 'APPEND', FILE = 'data.dat', FORM = 'FORMATTED')
!the algorithm
DO i=1,n
gaya=-k*x
a=gaya/m
dv=a*dt
v=v+dv
dx=v*dt
x=x+dx

ygaya=-ky*y
ay=ygaya/m
dvy=ay*dt
vy=vy+dvy
dy=vy*dt
y=y+dy
t=t+dt

!write the result of calclation to data.dat
WRITE(80,81) i, t, x, y
81 FORMAT(i7,' 'e14.7,' ',e14.7,' ',e14.7)
END DO

CLOSE(80)

END PROGRAM Grafik
!===========================================

save to grafik.f90 then compile using this syntax
$gfortran grafik.f90

that'll produce file named a.out

run using
$./a.out

and data.dat will appear
to plot the graphic using value in data.dat I use kst

$kst -x 2 -y 3 data dat

mean kst will use 2nd column as x-axis n 3rd as y-axis

Yeah, I know that the steps look boring, so I used sh script below to generate it automatically.
using kwrite, create text file like below:
rm *.dat
gfortran grafik.f90
./a.out
kst -x 2 -y 3 data.dat

save as run.sh, make it executable then run:
$./run.sh

!I also used script below to generate x, y, z in text file and plot it using kst
!
!DO i=1 ,100
! dt=i
! dt=dt/100
! sbx=r*sin(dt)
! sby=r*cos(dt)
! sbz=dt
! WRITE(80,81) sbx, sby, sbz
! 81 FORMAT(F10.2,' ',e14.7,' ',e14.7)
!END DO

!DO i=1, n
!DO j=1, n
! theta=i
! phi=j
! sbx=r*sin(theta)*cos(phi)
! sby=r*sin(theta)*sin(phi)
! sbz=r*cos(theta)
! !sbz=2
! WRITE(80,81) i, j, sbx, sby, sbz
! 81 FORMAT(i7,' ',i7,' 'e14.7,' ',e14.7,' ',e14.7)
! PRINT*, 'theta: ',i,' -------------'
! PRINT*, 'phi: ',j,' -------------'
! PRINT*, 'sb-x :', sbx
! PRINT*, 'sb-y :', sby
! PRINT*, 'sb-z :', sbz
!END DO
!END DO

There is something strange in two script above. The result is x, y, z (THREE variable) but why the plot is just in TWO axis? Err..., that the weakness of kst.

At prior time :), I used gnuplot to generate "3D" picture--of course, it just projection of z-axis (or x-axis if you using left-handed coordinate)--but I have'nt yet found to automating it using .sh script.

If you like to using gnuplot:
$gnuplot
>plot "data.dat" using 2:3 (oops, that still 2D. Plotting data.dat using 2nd and 3rd column)

>splot "data.dat" using 2:3:4 (that is.)

I've skimmed "man gnuplot" but did'nt found how to do it automatically

anybody can help me automating it using gnuplot?

oh yeah, almost forget, I use Linux.

night

I lay in the bed
hearing a crow of bats

it's night and no one here but me

I won't die tonight, maybe
but I did'nt felt live

Even my head is full of inspiration
my spirit is empty

someone
help me
blow my attitude

that's what I need at now