numpy.interp — NumPy v1.11 Manual (original) (raw)

numpy.interp(x, xp, fp, left=None, right=None, period=None)[source]¶

One-dimensional linear interpolation.

Returns the one-dimensional piecewise linear interpolant to a function with given values at discrete data-points.

Parameters:	x : array_like The x-coordinates of the interpolated values. xp : 1-D sequence of floats The x-coordinates of the data points, must be increasing if argument_period_ is not specified. Otherwise, xp is internally sorted after normalizing the periodic boundaries with xp = xp % period. fp : 1-D sequence of floats The y-coordinates of the data points, same length as xp. left : float, optional Value to return for x < xp[0]_, default is _fp[0]_. right* : float, optional Value to return for _x > xp[-1], default is fp[-1]. period* : None or float, optional A period for the x-coordinates. This parameter allows the proper interpolation of angular x-coordinates. Parameters left and _right_are ignored if period is specified. New in version 1.10.0.
Returns:	y : float or ndarray The interpolated values, same shape as x.
Raises:	ValueError If xp and fp have different length If xp or fp are not 1-D sequences If period == 0

Parameters:

x : array_like The x-coordinates of the interpolated values. xp : 1-D sequence of floats The x-coordinates of the data points, must be increasing if argument_period_ is not specified. Otherwise, xp is internally sorted after normalizing the periodic boundaries with xp = xp % period. fp : 1-D sequence of floats The y-coordinates of the data points, same length as xp. left : float, optional Value to return for x < xp[0]_, default is _fp[0]_. **right** : float, optional Value to return for _x > xp[-1], default is fp[-1]. period : None or float, optional A period for the x-coordinates. This parameter allows the proper interpolation of angular x-coordinates. Parameters left and _right_are ignored if period is specified. New in version 1.10.0.

Returns:

y : float or ndarray The interpolated values, same shape as x.

Raises:

ValueError If xp and fp have different length If xp or fp are not 1-D sequences If period == 0

Notes

Does not check that the x-coordinate sequence xp is increasing. If xp is not increasing, the results are nonsense. A simple check for increasing is:

Examples

xp = [1, 2, 3] fp = [3, 2, 0] np.interp(2.5, xp, fp) 1.0 np.interp([0, 1, 1.5, 2.72, 3.14], xp, fp) array([ 3. , 3. , 2.5 , 0.56, 0. ]) UNDEF = -99.0 np.interp(3.14, xp, fp, right=UNDEF) -99.0

Plot an interpolant to the sine function:

x = np.linspace(0, 2np.pi, 10) y = np.sin(x) xvals = np.linspace(0, 2np.pi, 50) yinterp = np.interp(xvals, x, y) import matplotlib.pyplot as plt plt.plot(x, y, 'o') [<matplotlib.lines.Line2D object at 0x...>] plt.plot(xvals, yinterp, '-x') [<matplotlib.lines.Line2D object at 0x...>] plt.show()

(Source code, png, pdf)

../../_images/numpy-interp-1_00_00.png

Interpolation with periodic x-coordinates:

x = [-180, -170, -185, 185, -10, -5, 0, 365] xp = [190, -190, 350, -350] fp = [5, 10, 3, 4] np.interp(x, xp, fp, period=360) array([7.5, 5., 8.75, 6.25, 3., 3.25, 3.5, 3.75])

()