Bairstow's method with Newton-Raphson in Fortran

[moebot]

this is bairstow's method , i need to put Newton-raphson in a subroutine and i don't know what's wrong i keep getting the wrong answer when i execute please help

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 :)

 

[FactChecker]

Have you run an example problem with known intermediate values and checked them? If so, where do they start to disagree?

 

[magoo]

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.

 

[Mark44]

You have extra spaces in the following code:

I don't believe this makes any difference whatsoever.

 

[aphirst]

@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

?

 

[jtbell]

I hope that after more than three months, moebot has gotten his code to work...

 

[moebot]

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 a lot for the help.

p.s i got the code to work ! haha