Function laplacian_kernel 

pub fn laplacian_kernel(
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f64,
    vsy: f64,
    vsz: f64,
    negative: bool,
) -> Vec<f64>

Generate Laplacian kernel in image space

Creates a 7-point stencil Laplacian centered at (0,0,0) for FFT compatibility. The stencil is: [-2(1/dx² + 1/dy² + 1/dz²)] at center, [1/dx²] at ±1 in x, [1/dy²] at ±1 in y, [1/dz²] at ±1 in z.

Arguments

• nx, ny, nz - Array dimensions
• vsx, vsy, vsz - Voxel sizes in mm
• negative - If true, return negative Laplacian

Returns

Flattened Laplacian kernel array of size nxnynz in C order