arange function
(Shortest import: from brian2 import arange)
- brian2.units.unitsafefunctions.arange([start, ]stop, [step, ]dtype=None, *, device=None, like=None)[source]
Return evenly spaced values within a given interval.
arange
can be called with a varying number of positional arguments:arange(stop)
: Values are generated within the half-open interval[0, stop)
(in other words, the interval includingstart
but excludingstop()
).arange(start, stop)
: Values are generated within the half-open interval[start, stop)
.arange(start, stop, step)
Values are generated within the half-open interval[start, stop)
, with spacing between values given bystep
.
For integer arguments the function is roughly equivalent to the Python built-in
range
, but returns an ndarray rather than arange
instance.When using a non-integer step, such as 0.1, it is often better to use
numpy.linspace
.See the Warning sections below for more information.
- Parameters:
start : integer or real, optional
Start of interval. The interval includes this value. The default start value is 0.
stop : integer or real
End of interval. The interval does not include this value, except in some cases where
step
is not an integer and floating point round-off affects the length ofout
.step : integer or real, optional
Spacing between values. For any output
out
, this is the distance between two adjacent values,out[i+1] - out[i]
. The default step size is 1. Ifstep
is specified as a position argument,start
must also be given.dtype : dtype, optional
The type of the output array. If
dtype
is not given, infer the data type from the other input arguments.device : str, optional
The device on which to place the created array. Default:
None
. For Array-API interoperability only, so must be"cpu"
if passed.Added in version 2.0.0.
like : array_like, optional
Reference object to allow the creation of arrays which are not NumPy arrays. If an array-like passed in as
like
supports the__array_function__
protocol, the result will be defined by it. In this case, it ensures the creation of an array object compatible with that passed in via this argument.Added in version 1.20.0.
- Returns:
arange : ndarray
Array of evenly spaced values.
For floating point arguments, the length of the result is
ceil((stop - start)/step)
. Because of floating point overflow, this rule may result in the last element ofout
being greater thanstop()
.
Warning
The length of the output might not be numerically stable.
Another stability issue is due to the internal implementation of
numpy.arange
. The actual step value used to populate the array isdtype(start + step) - dtype(start)
and notstep
. Precision loss can occur here, due to casting or due to using floating points whenstart
is much larger thanstep
. This can lead to unexpected behaviour. For example:>>> np.arange(0, 5, 0.5, dtype=int) array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0]) >>> np.arange(-3, 3, 0.5, dtype=int) array([-3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8])
In such cases, the use of
numpy.linspace
should be preferred.The built-in
range
generates Python built-in integers that have arbitrary size, whilenumpy.arange
producesnumpy.int32
ornumpy.int64
numbers. This may result in incorrect results for large integer values:>>> power = 40 >>> modulo = 10000 >>> x1 = [(n ** power) % modulo for n in range(8)] >>> x2 = [(n ** power) % modulo for n in np.arange(8)] >>> print(x1) [0, 1, 7776, 8801, 6176, 625, 6576, 4001] # correct >>> print(x2) [0, 1, 7776, 7185, 0, 5969, 4816, 3361] # incorrect
See also
numpy.linspace
Evenly spaced numbers with careful handling of endpoints.
numpy.ogrid
Arrays of evenly spaced numbers in N-dimensions.
numpy.mgrid
Grid-shaped arrays of evenly spaced numbers in N-dimensions.
Examples
>>> import numpy as np >>> np.arange(3) array([0, 1, 2]) >>> np.arange(3.0) array([ 0., 1., 2.]) >>> np.arange(3,7) array([3, 4, 5, 6]) >>> np.arange(3,7,2) array([3, 5])