FIND_ROOT_POL.f90 File Reference

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Functions/Subroutines
real *8 function	find_root_pol (x1, x2, xacc, n)
	Find a root of a polynomial of degree n.

Function/Subroutine Documentation

find_root_pol()

real*8 function find_root_pol	(		x1,
			x2,
			xacc,
			n
	)

Find a root of a polynomial of degree n.

Author

Ilario Mazzieri

Date

September, 2013 - Creation

Version

1.0

Parameters

[in]	x1	left bound of the interval [x1,x2]
[in]	x2	right bound of the interval [x1,x2]
[in]	xacc	acceleration parameter
[in]	n	polynomial degree
[out]	FIND_ROOT_POL	zero of the polynomial function of order n

Definition at line 30 of file FIND_ROOT_POL.f90.

 
      use speed_exit_codes
      
      implicit real*8(a-h,o-z)
      
      parameter(jmax=1000)
      
      call get_legendre_value(p2,fmid,p1,p1der,n,x2)
      call get_legendre_value(p2,f,p1,p1der,n,x1)
 
      if (f*fmid .ge. 0.d0) then
        write(*,*) 'root non-bracketed !'
        call exit(exit_root)
      endif
      
      if (f .lt. 0.d0) then
        find_root_pol = x1
        dx = x2 - x1
      else
        find_root_pol = x2
        dx = x1 - x2
      endif
      
      do j = 1,jmax
        dx = 0.5d0*dx
        xmid = find_root_pol + dx
        call get_legendre_value(p2,fmid,p1,p1der,n,xmid)
        if (fmid .le. 0.d0) find_root_pol = xmid
        
        if (dabs(dx) .lt. xacc .and. dabs(fmid) .le. xacc) then
          find_root_pol = xmid
          return
        endif
        
      enddo
      

References speed_exit_codes::exit_root, find_root_pol(), and get_legendre_value().

Referenced by find_root_pol(), make_lgl_nodes(), and make_lgl_nw().

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