A Python package for finite difference numerical derivatives in any number of dimensions.
- Differentiate arrays of any number of dimensions along any axis
- Partial derivatives of any desired order
- Any accuracy order can be specified
- Accurate treatment of grid boundary
- Includes standard operators from vector calculus like gradient, divergence and curl
- Can handle uniform and non-uniform grids
- Can handle arbitrary linear combinations of derivatives with constant and variable coefficients
- Fully vectorized for speed
- Calculate raw finite difference coefficients for any order and accuracy for uniform and non-uniform grids
findiff works in any number of dimensions. But for the sake of demonstration, suppose you
want to differentiate a four-dimensional function given on a 4D array f
with coordinates x, y, z, u
.
For , where x denotes the 0-th axis, we can write
# define operator
d_dx = FinDiff(0, dx)
# apply operator
df_dx = d_dx(f)
# df_dx is now an array of the same shape as f containing the partial derivative
The partial derivative , where z means the 2nd axis, is
d_dz = FinDiff(2, dz)
df_dz = d_dz(f)
Higher derivatives like
or
can be defined like
# the derivative order is the third argument
d2_dx2 = FinDiff(0, dx, 2)
d2f_dx2 = d2_dx2(f)
d4_dy4 = FinDiff(1, dy, 4)
d4f_dy4 = d4_dy4(f)
Mixed partial derivatives like
or
d2_dxdz = FinDiff((0, dx), (2, dz))
d2_dxdz(f)
d3_dx2dz = FinDiff((0, dx, 2), (2, dz))
You can also create linear combinations of differential operators like
diff_op = Coef(2) * FinDiff((0, dx, 2), (2, dz, 1)) + Coef(3) * FinDiff((0, dx, 1), (1, dy, 2))
and more general with variable coefficients like
isfrom numpy import meshgrid, sin
X, Y, Z, U = meshgrid(x, y, z, u, indexing="ij")
diff_op = Coef(2*X) * FinDiff((0, dz, 2), (2, dz, 1)) + Coef(3*sin(Y)*Z**2) * FinDiff((0, dx, 1), (1, dy, 2))
Chaining differential operators is also possible, e.g.
diff_op = (FinDiff(0, dx) - FinDiff(1, dy)) * (FinDiff(0, dx) + FinDiff(1, dy))
# is equivalent to
diff_op2 = FinDiff(0, dx, 2) - FinDiff(1, dy, 2)
Standard operators from vector calculus like gradient, divergence and curl are also available, for example:
grad = Gradient(h=[dx, dy, dz, du])
grad_f = grad(f)
More examples, including linear combinations with variable coefficients can be found here.
The package can work with any number of dimensions, the generalization of usage is straight forward. The only limit is memory and CPU speed.
When constructing an instance of FinDiff
, you can request the desired accuracy
order by setting the keyword argument acc
.
d2_dx2 = findiff.FinDiff(0, dy, 2, acc=4)
d2f_dx2 = d2_dx2(f)
If not specified, second order accuracy will be taken by default.
Sometimes you may want to have the raw finite difference coefficients.
These can be obtained for any derivative and accuracy order
using findiff.coefficients(deriv, acc)
. For instance,
import findiff
coefs = findiff.coefficients(deriv=2, acc=2)
gives
{ 'backward': {'coefficients': array([-1., 4., -5., 2.]),
'offsets': array([-3, -2, -1, 0])},
'center': {'coefficients': array([ 1., -2., 1.]),
'offsets': array([-1, 0, 1])},
'forward': {'coefficients': array([ 2., -5., 4., -1.]),
'offsets': array([0, 1, 2, 3])}
}
Simply use pip:
pip install findiff
You can find the documentation of the code including examples of application at https://maroba.github.io/findiff-docs/index.html.
findiff uses numpy for fast array processing.