ndarray/
logspace.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
// Copyright 2014-2016 bluss and ndarray developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![cfg(feature = "std")]
use num_traits::Float;

/// An iterator of a sequence of logarithmically spaced number.
///
/// Iterator element type is `F`.
pub struct Logspace<F> {
    sign: F,
    base: F,
    start: F,
    step: F,
    index: usize,
    len: usize,
}

impl<F> Iterator for Logspace<F>
where
    F: Float,
{
    type Item = F;

    #[inline]
    fn next(&mut self) -> Option<F> {
        if self.index >= self.len {
            None
        } else {
            // Calculate the value just like numpy.linspace does
            let i = self.index;
            self.index += 1;
            let exponent = self.start + self.step * F::from(i).unwrap();
            Some(self.sign * self.base.powf(exponent))
        }
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let n = self.len - self.index;
        (n, Some(n))
    }
}

impl<F> DoubleEndedIterator for Logspace<F>
where
    F: Float,
{
    #[inline]
    fn next_back(&mut self) -> Option<F> {
        if self.index >= self.len {
            None
        } else {
            // Calculate the value just like numpy.linspace does
            self.len -= 1;
            let i = self.len;
            let exponent = self.start + self.step * F::from(i).unwrap();
            Some(self.sign * self.base.powf(exponent))
        }
    }
}

impl<F> ExactSizeIterator for Logspace<F> where Logspace<F>: Iterator {}

/// An iterator of a sequence of logarithmically spaced numbers.
///
/// The `Logspace` has `n` elements, where the first element is `base.powf(a)`
/// and the last element is `base.powf(b)`.  If `base` is negative, this
/// iterator will return all negative values.
///
/// The iterator element type is `F`, where `F` must implement `Float`, e.g.
/// `f32` or `f64`.
///
/// **Panics** if converting `n - 1` to type `F` fails.
#[inline]
pub fn logspace<F>(base: F, a: F, b: F, n: usize) -> Logspace<F>
where
    F: Float,
{
    let step = if n > 1 {
        let num_steps = F::from(n - 1).expect("Converting number of steps to `A` must not fail.");
        (b - a) / num_steps
    } else {
        F::zero()
    };
    Logspace {
        sign: base.signum(),
        base: base.abs(),
        start: a,
        step,
        index: 0,
        len: n,
    }
}

#[cfg(test)]
mod tests {
    use super::logspace;

    #[test]
    #[cfg(feature = "approx")]
    fn valid() {
        use crate::{arr1, Array1};
        use approx::assert_abs_diff_eq;

        let array: Array1<_> = logspace(10.0, 0.0, 3.0, 4).collect();
        assert_abs_diff_eq!(array, arr1(&[1e0, 1e1, 1e2, 1e3]));

        let array: Array1<_> = logspace(10.0, 3.0, 0.0, 4).collect();
        assert_abs_diff_eq!(array, arr1(&[1e3, 1e2, 1e1, 1e0]));

        let array: Array1<_> = logspace(-10.0, 3.0, 0.0, 4).collect();
        assert_abs_diff_eq!(array, arr1(&[-1e3, -1e2, -1e1, -1e0]));

        let array: Array1<_> = logspace(-10.0, 0.0, 3.0, 4).collect();
        assert_abs_diff_eq!(array, arr1(&[-1e0, -1e1, -1e2, -1e3]));
    }

    #[test]
    fn iter_forward() {
        let mut iter = logspace(10.0f64, 0.0, 3.0, 4);

        assert!(iter.size_hint() == (4, Some(4)));

        assert!((iter.next().unwrap() - 1e0).abs() < 1e-5);
        assert!((iter.next().unwrap() - 1e1).abs() < 1e-5);
        assert!((iter.next().unwrap() - 1e2).abs() < 1e-5);
        assert!((iter.next().unwrap() - 1e3).abs() < 1e-5);
        assert!(iter.next().is_none());

        assert!(iter.size_hint() == (0, Some(0)));
    }

    #[test]
    fn iter_backward() {
        let mut iter = logspace(10.0f64, 0.0, 3.0, 4);

        assert!(iter.size_hint() == (4, Some(4)));

        assert!((iter.next_back().unwrap() - 1e3).abs() < 1e-5);
        assert!((iter.next_back().unwrap() - 1e2).abs() < 1e-5);
        assert!((iter.next_back().unwrap() - 1e1).abs() < 1e-5);
        assert!((iter.next_back().unwrap() - 1e0).abs() < 1e-5);
        assert!(iter.next_back().is_none());

        assert!(iter.size_hint() == (0, Some(0)));
    }
}