My code compiles, but it is not running properly. I'm not sure whether its inability to run is due to a mathematical error and/or if there is an issue in my coding syntax. The code is shown below. If anyone could me figure out what is wrong, please let me know.
Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
Backtrace for this error:
#0 0x7F1E52D74E08
#1 0x7F1E52D73F90
#2 0x7F1E526BB4AF
#3 0x400BBC in legendrepoly.3381 at project.f90:?
#4 0x40138C in MAIN__ at project.f90:?
Segmentation fault (core dumped)
program Project
use iso_fortran_env
implicit none
integer(int32) :: Nmax ! maximum order of Legendre polynomial
integer(int32) :: step ! step size in angle from 0 to 180 degrees
real(real64), parameter :: pi=3.1415926
real(real64) :: mu
real(real64) :: theta=0
real(real64), dimension(:,:), allocatable :: P, dP ! Legendre polynomial
integer(int32) :: k, h, i, n, l
! User Input
print *, "Please enter maximum order of Legendre polynomials:"
read (*,*) Nmax
print *, "Please enter integer step size (in degrees between 0 and 180):"
read (*,*) step
! Output
mu = cos(theta*(pi/180.0_real64))
k = 180.0/step
h = 2*cos(real(step)*(pi/180.0_real64))
allocate ( P(Nmax+1,180) )
allocate ( dP(Nmax+1,180) )
call legendrepoly(l,mu,Nmax,step)
print *, dP
contains
subroutine legendrepoly(l,mu,Nmax,step)
real(real64), dimension(:,:), allocatable :: P, dP
real(real64) :: a
real(real64), intent(in) :: mu
integer(int32) :: i, Nmax, step
integer(int32), intent(in) :: l
a = real(l)
do i = 1, 181, step
P(1,i-1) = 1.0
P(2,i-1) = mu
end do
do i = 1, 181, step
do n = 2, Nmax
P(l+1,i-1) = ((2.0*a+1.0) * mu * P(l,i-1) - a*P(l-1,i-1)) / (a+1.0)
dP(l+1,i-1) = (P(l+1,i)-P(l+1,i-2))/2
end do
end do
end subroutine legendrepoly
end program Project
