jax.numpy.ptp

jax.numpy.ptp(a, axis=None, out=None, keepdims=False)[source]

Range of values (maximum - minimum) along an axis.

LAX-backend implementation of ptp(). Original docstring below.

The name of the function comes from the acronym for ‘peak to peak’.

Warning

ptp preserves the data type of the array. This means the return value for an input of signed integers with n bits (e.g. np.int8, np.int16, etc) is also a signed integer with n bits. In that case, peak-to-peak values greater than 2**(n-1)-1 will be returned as negative values. An example with a work-around is shown below.

Parameters
  • a (array_like) – Input values.

  • axis (None or int or tuple of ints, optional) – Axis along which to find the peaks. By default, flatten the array. axis may be negative, in which case it counts from the last to the first axis.

  • out (array_like) – Alternative output array in which to place the result. It must have the same shape and buffer length as the expected output, but the type of the output values will be cast if necessary.

  • keepdims (bool, optional) – If this is set to True, the axes which are reduced are left in the result as dimensions with size one. With this option, the result will broadcast correctly against the input array.

Returns

ptp – A new array holding the result, unless out was specified, in which case a reference to out is returned.

Return type

ndarray

Examples

>>> x = np.array([[4, 9, 2, 10],
...               [6, 9, 7, 12]])
>>> np.ptp(x, axis=1)
array([8, 6])
>>> np.ptp(x, axis=0)
array([2, 0, 5, 2])
>>> np.ptp(x)
10

This example shows that a negative value can be returned when the input is an array of signed integers.

>>> y = np.array([[1, 127],
...               [0, 127],
...               [-1, 127],
...               [-2, 127]], dtype=np.int8)
>>> np.ptp(y, axis=1)
array([ 126,  127, -128, -127], dtype=int8)

A work-around is to use the view() method to view the result as unsigned integers with the same bit width:

>>> np.ptp(y, axis=1).view(np.uint8)
array([126, 127, 128, 129], dtype=uint8)