Computes the numerical Laplacian of functions
or the symbolic Laplacian of characters
in arbitrary orthogonal coordinate systems.
laplacian(
f,
var,
params = list(),
coordinates = "cartesian",
accuracy = 4,
stepsize = NULL,
drop = TRUE
)
f %laplacian% var
array of characters
or a function
returning a numeric
array.
vector giving the variable names with respect to which the derivatives are to be computed and/or the point where the derivatives are to be evaluated. See derivative
.
list
of additional parameters passed to f
.
coordinate system to use. One of: cartesian
, polar
, spherical
, cylindrical
, parabolic
, parabolic-cylindrical
or a vector of scale factors for each varibale.
degree of accuracy for numerical derivatives.
finite differences stepsize for numerical derivatives. It is based on the precision of the machine by default.
if TRUE
, return the Laplacian as a scalar and not as an array
for scalar-valued functions.
Scalar for scalar-valued functions when drop=TRUE
, array
otherwise.
The Laplacian is a differential operator given by the divergence of the
gradient of a scalar-valued function \(F\), resulting in a scalar value giving
the flux density of the gradient flow of a function.
The laplacian
is computed in arbitrary orthogonal coordinate systems using
the scale factors \(h_i\):
$$\nabla^2F = \frac{1}{J}\sum_i\partial_i\Biggl(\frac{J}{h_i^2}\partial_iF\Biggl)$$
where \(J=\prod_ih_i\). When the function \(F\) is a tensor-valued function
\(F_{d_1\dots d_n}\), the laplacian
is computed for each scalar component:
$$(\nabla^2F)_{d_1\dots d_n} = \frac{1}{J}\sum_i\partial_i\Biggl(\frac{J}{h_i^2}\partial_iF_{d_1\dots d_n}\Biggl)$$
f %laplacian% var
: binary operator with default parameters.
Guidotti E (2022). "calculus: High-Dimensional Numerical and Symbolic Calculus in R." Journal of Statistical Software, 104(5), 1-37. doi:10.18637/jss.v104.i05
Other differential operators:
curl()
,
derivative()
,
divergence()
,
gradient()
,
hessian()
,
jacobian()
### symbolic Laplacian
laplacian("x^3+y^3+z^3", var = c("x","y","z"))
#> [1] "3 * (2 * x) + 3 * (2 * y) + 3 * (2 * z)"
### numerical Laplacian in (x=1, y=1, z=1)
f <- function(x, y, z) x^3+y^3+z^3
laplacian(f = f, var = c(x=1, y=1, z=1))
#> [1] 18
### vectorized interface
f <- function(x) sum(x^3)
laplacian(f = f, var = c(1, 1, 1))
#> [1] 18
### symbolic vector-valued functions
f <- array(c("x^2","x*y","x*y","y^2"), dim = c(2,2))
laplacian(f = f, var = c("x","y"))
#> [,1] [,2]
#> [1,] "2" "0"
#> [2,] "0" "2"
### numerical vector-valued functions
f <- function(x, y) array(c(x^2,x*y,x*y,y^2), dim = c(2,2))
laplacian(f = f, var = c(x=0,y=0))
#> [,1] [,2]
#> [1,] 2 0
#> [2,] 0 2
### binary operator
"x^3+y^3+z^3" %laplacian% c("x","y","z")
#> [1] "3 * (2 * x) + 3 * (2 * y) + 3 * (2 * z)"