sqrt function fortran 90 error - fortran90

Question

I am trying to handle sqrt but somehow I cannot understand why when compiling this program, there goes a segmentation fault error. I have detected that it is because of the sqrt. But how can I manage to use sqrt in these type of formulations without mistaking?
SUBROUTINE constructImages(image,w,w_b,x_w)
USE cellConst
USE simParam, ONLY: xDim, yDim, obstX, obstY, obstR,L_max
USE D2Q9Const, ONLY: v
implicit none
integer, INTENT(INOUT):: image(yDim,xDim),w_b(yDim,xDim),w(yDim,xDim)
double precision, dimension(L_max,0:1), INTENT(INOUT):: x_w
integer:: x,y,i,cont_L
double precision::x2,y2
!Disk Shape
do x = 1, xDim
do y = 1, yDim
if (((x-obstX)**2.0d0 + (y-obstY)**2.0d0) <= (obstR**2.0d0) ) then
image(y,x) = wall
w(y,x) = wall
end if
end do
end do
do x = 1, xDim
do y = 3, yDim-2
do i= 1,8
if ((w(y,x) == fluid) .and. (w(y+v(i,1),x+v(i,0)) == wall)) then
w_b(y,x) = 2
end if
end do
end do
end do
do x = 1,xDim
do y = 3, yDim-2
if (w_b(y,x) == 2) then
w_b(y,x) = wall
w(y,x) = wall
image(y,x) = wall
end if
end do
end do
x_w = 0.0d0 !Lagrangian vector for boundary exact position
cont_L = 0
do x = 1, xDim
do y = 1, yDim
do i = 1, 8
if ((w(y+v(i,1),x+v(i,0)) == fluid) .and. (w_b(y,x) == wall)) then
cont_L = cont_L +1
. x_w(cont_L,0) = x2 - ((x-obstX)^2.0d0 + (y-obstY)^2.0d0)^0.5d0 - obstR
. x_w(cont_L,1) = y2 - ((x-obstX)^2.0d0 + (y-obstY)^2.0d0)^0.5d0 - obstR
! write(*,*) x2,y2
! write(*,*) x_w(cont_L,0),x_w(cont_L,1)
end if
end do
end do
end do
END SUBROUTINE constructImages
Please, let me know if more information is required,
sincerely,
Albert P
PD, the 3 integer eulerian meshes are 0 / 1 2D meshes where 1 is assigned to a wall, which is delimited by a rounded disk, w_b(y,x) are the boundary points, w(y,x) are the whole disk points and x_w I want to set a langrangian vector of the discretized exact position for the obstacle. Don't really need to understand this.

Answer 1

The problem was actually an array index which was under 1 in w, and there were multiple problems that somehow derived to that error when setting sqrt.
do x = 1, xDim
do y = 1, yDim
do i = 1, 8
if ((w(y,x) == fluid) .and. (w(y+v(i,1),x+v(i,0)) == wall))
.....
here I state that w goes >1, and then it gets out of the bounds.
I have solved the problem not letting the integers go below 1 and over yDim, and this with all the routines, and I have detected that problem with a check-bounce while executing the code.
Thank you all of you anyway. That was a tough one!!
Albert P