I need help in Fortran please -- Bairstow's method & Newton-Raphson

  • Fortran
  • Thread starter moebot
  • Start date
  • #1
5
2
this is bairstow's method , i need to put newton-raphson in a subroutine and i don't know whats wrong i keep getting the wrong answer when i execute please help

Code:
parameter (np=100)
parameter (eps=1e-3)
real a(np) ,b(np),c(np)
real r ,s ,ri,si   
integer n,i

write(*,*)'n,r,s'
read(*,*)n,r,s

    do i=n+1,1,-1
write(*,*)'a(i)'
read(*,*) a(i)
end do

10 ri=r
   si=s
   b(n+1)=a(n+1)
   b(n)=a(n)+r*b(n+1)
   do i=n-1,1,-1
   b(i)=a(i)+r*b(i+1)+s*b(i+2)
   end do

   c(n+1)=b(n+1)
   c(n)=b(n)+r*c(n+1)
   do i=n-1,1,-1
   c(i)=b(i)+r*c(i+1)+s*c(i+2)
   end do

   do i=n+1,1,-1
   write(*,*) i,a(i),b(i),c(i)
   end do
 
   write(*,*)
 
 
 
  d=c(3)*c(3)-c(2)*c(4)
  r=r-(1./d)*(c(3)*b(2)-c(4)*b(1))
  s=s-(1./d)*(-c(2)*b(2)+c(3)*b(1))


   if(sqrt(ri**2-r**2).ge.eps.or.sqrt(si**2-s**2).ge.eps)    goto 10
   write(*,*) r,s

 
   end

thanks in advance :)
 
Last edited by a moderator:

Answers and Replies

  • #2
FactChecker
Science Advisor
Gold Member
5,978
2,297
Have you run an example problem with known intermediate values and checked them? If so, where do they start to disagree?
 
  • #3
166
45
You have extra spaces in the following code:

real a(np) ,b(np),c(np)
real r ,s ,ri,si

I haven't used Fortran in many years, but I would make sure the unnecessary spaces are deleted and that you have spaces after the commas.
 
  • #4
34,530
6,226
You have extra spaces in the following code:
I don't believe this makes any difference whatsoever.
 
  • Like
Likes DrClaude
  • #5
aphirst
Gold Member
25
5
@moebot Are you able to provide some comments to your code, such as
  • What the equation is, whose root(s) you're trying to find
  • What you are intending each section of code to do
  • Why you're writing in F77 (fixed) style with GOTOs instead of loops
?
 
  • #6
jtbell
Mentor
15,720
3,851
I hope that after more than three months, moebot has gotten his code to work...
 
  • #7
5
2
I hope that after more than three months, moebot has gotten his code to work...
hahaha, i am doing my second degree now, and i just remembered this, thanks alot for the help.

p.s i got the code to work ! haha
 
  • Like
  • Haha
Likes jtbell and Tom.G

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