Function deriv_2d 

pub fn deriv_2d(
    data: &[f64],
    n: usize,
    argvals_s: &[f64],
    argvals_t: &[f64],
    m1: usize,
    m2: usize,
) -> Option<Deriv2DResult>

Compute 2D partial derivatives for surface data.

For a surface f(s,t), computes:

• ds: partial derivative with respect to s (∂f/∂s)
• dt: partial derivative with respect to t (∂f/∂t)
• dsdt: mixed partial derivative (∂²f/∂s∂t)

Arguments

• data - Column-major matrix, n surfaces, each stored as m1*m2 values
• n - Number of surfaces
• argvals_s - Grid points in s direction (length m1)
• argvals_t - Grid points in t direction (length m2)
• m1 - Grid size in s direction
• m2 - Grid size in t direction