I have recently started FORTRAN to learn Can any body explain, what these lines of code written in FORTRAN are doing...

 

 

!USE MSFLIB

use IFPORT

implicit none

integer nmax,i,m,v,c,j,d

parameter(nmax=50)

real*8 h,x(2),y(2),f(2),r1(2),r2(2),t

real*8 r3(2),r4(2),pi,tmax,ti,lam,k

character*20 data1

real*4 r,rr,z(nmax),p(nmax)

c Initial Values

!k=20

pi=4d0*atan(1d0)

do 200 j=1,nmax

z(j)=28*RAND()

!write(*,*) z(j) !50

p(j)=10*RAND() !10

200 continue

do 100 m=1,nmax

c=0

d=0

x(1)=z(m)

x(2)=p(m)

write(*,*) m, x(1),x(2)

tmax=1000*pi

h=pi/10000

k=0.5d0 !1.00026

v=4.0d0 !15.03

lam=0.90d0

c Oppening the Data File and Writting the Data in:

write(data1, '("a16.dat",i2.2)' )

open(11,file=data1,status='unknown')

close(11)

c**********************************************************************

do 10 ti=0,tmax,h

do 20 i=1,2

y(i)=x(i)

20 continue

t=ti

f(1)=x(2)

f(2)=-1d0+k*v*exp(-k*(x(1)-lam*sin(t)))

do 30 i=1,2

r1(i)=f(i)*h

x(i)=y(i)+r1(i)/2

30 continue

t=ti+h/2

All those lines?

 

Do you first understand that in Fortran you must 'declare the variables' and it is usual to collect all these together at the start for convenience?

 

So lines up to the starred lines are just declarations.

 

or

 

Are you asking about the subsequent do loops ?

 

If so what do you not understand about them?

Actually i wana know what are do loops doing..... their dry run is my need???

I am not getting are they nested loops or simple do loops??

please explain what function they are performing??

Here's a hint:

Start by asking yourself, if you understand the syntax required for an ordinary, non-nested loop?

 

Simple Non-nested loop example:

do 10 i = 1, 5
     i = i + 1
10 continue

If you understand the syntax for a non-nested loop, then you can move on to understanding nested loop syntax. 

Simple nested loop example (loop 20 is nested within loop 10):

do 10 i = 1, 5
     do 20 j = 1, 2
          j = j + 1
    20 continue
    i + i + 1
10 continue

If you understand these syntax, then you should be able to answer your question on your own

z(j)=28*RAND()

!write(*,*) z(j) !50

please explain these two lines

pi=4d0*atan(1d0)

do 200 j=1,nmax

z(j)=28*RAND()

!write(*,*) z(j) !50

explain please these lines

pi=4d0*atan(1d0)

what is ment by "do"????

Edited September 19, 201411 yr by saleha noor

what is ment by "do"????

seleha, if you don't know what a do loop is, you don't just need FORTRAN help, but introduction to programming. A do loop is a relatively basic building block that is in most general languages to allow you to repeat execution of lines of code.

 

Answering this question is beyond the scope of what a forum is intended to do.

 

You need to start with an introduction to programming class. Some examples of many: http://www.stat.tamu.edu/~jnewton/604/chap7.pdf http://www.lrsm.upenn.edu/~vitek/courses/f77intro/f77intro.pdf

 

There are many other books and online resources available. Search "introduction to programming" and "introduction to fortran"

Edited September 20, 201411 yr by Bignose

 

z(j)=28*RAND()

!write(*,*) z(j) !50

please explain these two lines

pi=4d0*atan(1d0)

do 200 j=1,nmax

z(j)=28*RAND()

!write(*,*) z(j) !50

explain please these lines

pi=4d0*atan(1d0)

what is ment by "do"????

 

Are you asking about do (as in do loop) or about d0 (which I believe is related to number type)?

Are you asking about do (as in do loop) or about d0 (which I believe is related to number type)?

Yeah. In fortran d makes the number a double instead of a single precision number. If you use e in exponential notation, the number is a single.

Edited September 21, 201411 yr by Bignose

pi=4d0*atan(1d0)

i am asking about this "1d0"???

i am not asking about do loop ..

pi=4d0*atan(1d0)

i am asking about this "1d0"???

i am not asking about do loop ..

 

From: http://math.hawaii.edu/wordpress/fortran-3/#double

 

Double precision numbers are written in scientific notation but with D usurping the role of E.

 

And: http://stackoverflow.com/questions/8434820/what-does-mean-10-d00-in-fortran