Finite difference coefficient

In mathematics, to approximate a derivative to an arbitrary order of accuracy, it is possible to use the finite difference. A finite difference can be central, forward or backward.

Central finite difference

This table contains the coefficients of the central differences, for several orders of accuracy:^[1]

Derivative	Accuracy	−4	−3	−2	−1	0	1	2	3	4
1	2				−1/2	0	1/2
	4			1/12	−2/3	0	2/3	−1/12
	6		−1/60	3/20	−3/4	0	3/4	−3/20	1/60
	8	1/280	−4/105	1/5	−4/5	0	4/5	−1/5	4/105	−1/280
2	2				1	−2	1
	4			−1/12	4/3	−5/2	4/3	−1/12
	6		1/90	−3/20	3/2	−49/18	3/2	−3/20	1/90
	8	−1/560	8/315	−1/5	8/5	−205/72	8/5	−1/5	8/315	−1/560
3	2			−1/2	1	0	−1	1/2
	4		1/8	−1	13/8	0	−13/8	1	−1/8
	6	−7/240	3/10	−169/120	61/30	0	−61/30	169/120	−3/10	7/240
4	2			1	−4	6	−4	1
	4		−1/6	2	−13/2	28/3	−13/2	2	−1/6
	6	7/240	−2/5	169/60	−122/15	91/8	−122/15	169/60	−2/5	7/240
5	2		−1/2	2	−5/2	0	5/2	−2	1/2
6	2		1	−6	15	−20	15	−6	1

For example, the third derivative with a second-order accuracy is

$\displaystyle f'''(x_{0}) \approx \displaystyle \frac{-\frac{1}{2}f(x_{-2}) + f(x_{-1}) -f(x_{+1}) +\frac{1}{2}f(x_{+2})}{h^3_x} + O\left(h_x^2 \right)$

where $h_x$ represents a uniform grid spacing between each finite difference interval.

Forward and backward finite difference

This table contains the coefficients of the forward differences, for several order of accuracy:^[1]

Derivative	Accuracy	0	1	2	3	4	5	6	7	8
1	1	−1	1
	2	−3/2	2	−1/2
	3	−11/6	3	−3/2	1/3
	4	−25/12	4	−3	4/3	−1/4
	5	−137/60	5	−5	10/3	−5/4	1/5
	6	−49/20	6	−15/2	20/3	−15/4	6/5	−1/6
2	1	1	−2	1
	2	2	−5	4	−1
	3	35/12	−26/3	19/2	−14/3	11/12
	4	15/4	−77/6	107/6	−13	61/12	−5/6
	5	203/45	−87/5	117/4	−254/9	33/2	−27/5	137/180
	6	469/90	−223/10	879/20	−949/18	41	−201/10	1019/180	−7/10
3	1	−1	3	−3	1
	2	−5/2	9	−12	7	−3/2
	3	−17/4	71/4	−59/2	49/2	−41/4	7/4
	4	−49/8	29	−461/8	62	−307/8	13	−15/8
	5	−967/120	638/15	−3929/40	389/3	−2545/24	268/5	−1849/120	29/15
	6	−801/80	349/6	−18353/120	2391/10	−1457/6	4891/30	−561/8	527/30	−469/240
4	1	1	−4	6	−4	1
	2	3	−14	26	−24	11	−2
	3	35/6	−31	137/2	−242/3	107/2	−19	17/6
	4	28/3	−111/2	142	−1219/6	176	−185/2	82/3	−7/2
	5	1069/80	−1316/15	15289/60	−2144/5	10993/24	−4772/15	2803/20	−536/15	967/240

For example, the first derivative with a third-order accuracy and the second derivative with a second-order accuracy are

$\displaystyle f'(x_{0}) \approx \displaystyle \frac{-\frac{11}{6}f(x_{0}) + 3f(x_{+1}) -\frac{3}{2}f(x_{+2}) +\frac{1}{3}f(x_{+3}) }{h_{x}} + O\left(h_{x}^3 \right),$

$\displaystyle f''(x_{0}) \approx \displaystyle \frac{2f(x_{0}) - 5f(x_{+1}) + 4f(x_{+2}) - f(x_{+3}) }{h_{x}^2} + O\left(h_{x}^2 \right),$

while the corresponding backward approximations are given by

$\displaystyle f'(x_{0}) \approx \displaystyle \frac{\frac{11}{6}f(x_{0}) - 3f(x_{-1}) +\frac{3}{2}f(x_{-2}) -\frac{1}{3}f(x_{-3}) }{h_{x}} + O\left(h_{x}^3 \right),$

$\displaystyle f''(x_{0}) \approx \displaystyle \frac{2f(x_{0}) - 5f(x_{-1}) + 4f(x_{-2}) - f(x_{-3}) }{h_{x}^2} + O\left(h_{x}^2 \right),$

In general, to get the coefficients of the backward approximations, give all odd derivatives listed in the table the opposite sign, whereas for even derivatives the signs stay the same. The following table illustrates this:

Derivative	Accuracy	−8	−7	−6	−5	−4	−3	−2	−1	0
1	1								−1	1
	2							1/2	−2	3/2
2	1							1	−2	1
	2						−1	4	−5	2
3	1						−1	3	−3	1
	2					3/2	−7	12	−9	5/2
4	1					1	−4	6	−4	1
	2				−2	11	−24	26	−14	3

See also

• Finite difference method
• Finite difference
• Five-point stencil

References

1. Fornberg, Bengt (1988), "Generation of Finite Difference Formulas on Arbitrarily Spaced Grids", Mathematics of Computation 51 (184): 699–706, doi:10.1090/S0025-5718-1988-0935077-0, ISSN 0025-5718.