doc(ai4dev): fix type in README

doc/ai4dev/README.md

@@ -16,7 +16,9 @@ Vibe Coding
 2. Edit `diffusion-app.F90` to remove the lines beginning and ending with 
    `module procedure laplacian` and `end procedure laplacian`, respectively.
 3. Enter the file `doc/ai4dev/vibe-coding/README.md` as your prompt and
-   attach the edited `diffusion-app.F90` file.
+   attach the edited `diffusion-app.F90` file. You might need to rename
+   the file to something like `diffusion-app.txt` for the file type to be
+   acccepted.
 4. Insert the resulting function into the `subdomain_s` submodule and
    try compiling and executing again to check the result.
 
@@ -29,6 +31,8 @@ Idiomtic Vibe Coding
 2. Edit `test-suite.F90` to remove the lines beginning and ending with 
    `module procedure laplacian` and `end procedure laplacian`, respectively.
 3. Enter the file `doc/ai4dev/idiomaic-vibe-coding/README.md` as your prompt 
-   and attach the edited `tgest-sutie.F90` file.
+   and attach the edited `test-suite.F90` file.  You might need to rename
+   the file to something like `test-suite.txt` for the file type to be
+   acccepted.
 4. Insert the resulting function into the `subdomain_s` submodule and
    try compiling and executing again to check the result.

doc/ai4dev/idiomatic-vibe-coding/idiomatic-vibe-response.f90

@@ -0,0 +1,90 @@
+pure module function laplacian(rhs) result(laplacian_rhs)
+  implicit none
+  class(subdomain_t), intent(in) :: rhs
+  type(subdomain_t) :: laplacian_rhs
+
+  ! Local variables for array bounds and grid spacing
+  integer :: my_nx, ny, nz, me, num_subdomains
+  real :: dx_val, dy_val, dz_val, dx2_inv, dy2_inv, dz2_inv
+
+  ! Get array dimensions and parallel image information
+  my_nx = size(rhs%s_, 1)
+  ny = size(rhs%s_, 2) 
+  nz = size(rhs%s_, 3)
+  me = this_image()
+  num_subdomains = num_images()
+
+  ! Get grid spacing values
+  dx_val = rhs%dx()
+  dy_val = rhs%dy() 
+  dz_val = rhs%dz()
+
+  ! Compute inverse squared grid spacings for efficiency
+  dx2_inv = 1.0 / (dx_val * dx_val)
+  dy2_inv = 1.0 / (dy_val * dy_val)
+  dz2_inv = 1.0 / (dz_val * dz_val)
+
+  ! Allocate result array with same shape as input
+  allocate(laplacian_rhs%s_(my_nx, ny, nz))
+
+  ! Initialize result to zero
+  laplacian_rhs%s_ = 0.0
+
+  ! Compute 2nd-order central difference Laplacian in interior points
+  ! Laplacian = d²/dx² + d²/dy² + d²/dz²
+  do concurrent (i = 2:my_nx-1, j = 2:ny-1, k = 2:nz-1) default(none) &
+    shared(laplacian_rhs, rhs, dx2_inv, dy2_inv, dz2_inv, my_nx, ny, nz, me, num_subdomains)
+
+    ! Second derivative in x-direction: (f(i+1) - 2*f(i) + f(i-1))/dx²
+    ! Second derivative in y-direction: (f(j+1) - 2*f(j) + f(j-1))/dy²  
+    ! Second derivative in z-direction: (f(k+1) - 2*f(k) + f(k-1))/dz²
+    laplacian_rhs%s_(i,j,k) = &
+      dx2_inv * (rhs%s_(i+1,j,k) - 2.0*rhs%s_(i,j,k) + rhs%s_(i-1,j,k)) + &
+      dy2_inv * (rhs%s_(i,j+1,k) - 2.0*rhs%s_(i,j,k) + rhs%s_(i,j-1,k)) + &
+      dz2_inv * (rhs%s_(i,j,k+1) - 2.0*rhs%s_(i,j,k) + rhs%s_(i,j,k-1))
+  end do
+
+  ! Handle boundary conditions at subdomain interfaces for x-direction
+  ! Left boundary (i=1) - only compute if not the first subdomain
+  if (me > 1) then
+    do concurrent (j = 2:ny-1, k = 2:nz-1) default(none) &
+      shared(laplacian_rhs, rhs, dx2_inv, dy2_inv, dz2_inv, ny, nz, halo_x)
+
+      laplacian_rhs%s_(1,j,k) = &
+        dx2_inv * (rhs%s_(2,j,k) - 2.0*rhs%s_(1,j,k) + halo_x(west,j,k)) + &
+        dy2_inv * (rhs%s_(1,j+1,k) - 2.0*rhs%s_(1,j,k) + rhs%s_(1,j-1,k)) + &
+        dz2_inv * (rhs%s_(1,j,k+1) - 2.0*rhs%s_(1,j,k) + rhs%s_(1,j,k-1))
+    end do
+  end if
+
+  ! Right boundary (i=my_nx) - only compute if not the last subdomain  
+  if (me < num_subdomains) then
+    do concurrent (j = 2:ny-1, k = 2:nz-1) default(none) &
+      shared(laplacian_rhs, rhs, dx2_inv, dy2_inv, dz2_inv, my_nx, ny, nz, halo_x, num_subdomains)
+
+      laplacian_rhs%s_(my_nx,j,k) = &
+        dx2_inv * (halo_x(east,j,k) - 2.0*rhs%s_(my_nx,j,k) + rhs%s_(my_nx-1,j,k)) + &
+        dy2_inv * (rhs%s_(my_nx,j+1,k) - 2.0*rhs%s_(my_nx,j,k) + rhs%s_(my_nx,j-1,k)) + &
+        dz2_inv * (rhs%s_(my_nx,j,k+1) - 2.0*rhs%s_(my_nx,j,k) + rhs%s_(my_nx,j,k-1))
+    end do
+  end if
+
+  ! Set boundary values to zero as specified
+  ! Y boundaries
+  laplacian_rhs%s_(:, 1, :) = 0.0
+  laplacian_rhs%s_(:, ny, :) = 0.0
+
+  ! Z boundaries  
+  laplacian_rhs%s_(:, :, 1) = 0.0
+  laplacian_rhs%s_(:, :, nz) = 0.0
+
+  ! X boundaries for first and last subdomains
+  if (me == 1) then
+    laplacian_rhs%s_(1, :, :) = 0.0
+  end if
+
+  if (me == num_subdomains) then
+    laplacian_rhs%s_(my_nx, :, :) = 0.0
+  end if
+
+end function laplacian

doc/ai4dev/vibe-coding/vibe-response.f90

@@ -0,0 +1,63 @@
+pure module function laplacian(rhs) result(laplacian_rhs)
+  implicit none
+  class(subdomain_t), intent(in) :: rhs
+  type(subdomain_t) :: laplacian_rhs
+  integer :: i, j, k
+
+  ! Step 1: Empty module procedure with comments explaining the computation
+  ! This function computes the 2nd-order central difference approximation 
+  ! to the Laplacian operator applied to the s_ component of the input subdomain
+
+  ! Step 2: Allocate the result's s_ component to shape [my_nx, ny, nz]
+  allocate(laplacian_rhs%s_(my_nx, ny, nz))
+
+  ! Step 3: Compute 2nd-order central difference Laplacian using do concurrent
+  ! Handle interior points (excluding boundaries and halo regions)
+  do concurrent(i=2:my_nx-1, j=2:ny-1, k=2:nz-1) default(none) shared(laplacian_rhs, rhs)
+    ! Step 4: Store Laplacian approximation in s_ component of result
+    ! Laplacian = d²/dx² + d²/dy² + d²/dz²
+    laplacian_rhs%s_(i,j,k) = &
+      (rhs%s_(i-1,j,k) - 2*rhs%s_(i,j,k) + rhs%s_(i+1,j,k))/dx_**2 + &
+      (rhs%s_(i,j-1,k) - 2*rhs%s_(i,j,k) + rhs%s_(i,j+1,k))/dy_**2 + &
+      (rhs%s_(i,j,k-1) - 2*rhs%s_(i,j,k) + rhs%s_(i,j,k+1))/dz_**2
+  end do
+
+  ! Handle western boundary points (i=1) with halo exchange
+  if (me /= 1) then
+    ! Step 5: Use halo_x(west,:,:) when me==1 and accessing rhs%s_(1,:,:)
+    do concurrent(j=2:ny-1, k=2:nz-1) default(none) shared(laplacian_rhs, rhs)
+      laplacian_rhs%s_(1,j,k) = &
+        (halo_x(west,j,k) - 2*rhs%s_(1,j,k) + rhs%s_(2,j,k))/dx_**2 + &
+        (rhs%s_(1,j-1,k) - 2*rhs%s_(1,j,k) + rhs%s_(1,j+1,k))/dy_**2 + &
+        (rhs%s_(1,j,k-1) - 2*rhs%s_(1,j,k) + rhs%s_(1,j,k+1))/dz_**2
+    end do
+  end if
+
+  ! Handle eastern boundary points (i=my_nx) with halo exchange
+  if (me /= num_subdomains) then
+    ! Step 5: Use halo_x(east,:,:) when me==num_subdomains and accessing rhs%s_(my_nx,:,:)
+    do concurrent(j=2:ny-1, k=2:nz-1) default(none) shared(laplacian_rhs, rhs)
+      laplacian_rhs%s_(my_nx,j,k) = &
+        (rhs%s_(my_nx-1,j,k) - 2*rhs%s_(my_nx,j,k) + halo_x(east,j,k))/dx_**2 + &
+        (rhs%s_(my_nx,j-1,k) - 2*rhs%s_(my_nx,j,k) + rhs%s_(my_nx,j+1,k))/dy_**2 + &
+        (rhs%s_(my_nx,j,k-1) - 2*rhs%s_(my_nx,j,k) + rhs%s_(my_nx,j,k+1))/dz_**2
+    end do
+  end if
+
+  ! Step 6: Set boundary conditions - zero Laplacian at domain boundaries
+  laplacian_rhs%s_(:, 1, :) = 0.  ! j=1 boundary
+  laplacian_rhs%s_(:, ny, :) = 0. ! j=ny boundary
+  laplacian_rhs%s_(:, :, 1) = 0.  ! k=1 boundary
+  laplacian_rhs%s_(:, :, nz) = 0. ! k=nz boundary
+
+  ! Step 7: Set western domain boundary to zero if this is the first subdomain
+  if (me == 1) then
+    laplacian_rhs%s_(1, :, :) = 0.
+  end if
+
+  ! Step 8: Set eastern domain boundary to zero if this is the last subdomain
+  if (me == num_subdomains) then
+    laplacian_rhs%s_(my_nx, :, :) = 0.
+  end if
+
+end function