use-strain 0.0.1

Primitive engineering strain helpers
Documentation 
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

#![forbid(unsafe_code)]
//! Primitive strain helpers.
//!
//! Initial calculations assume SI units unless otherwise documented.
//!
//! # Examples
//!
//! ```rust
//! use use_strain::{Strain, engineering_strain, percent_strain, strain_from_change};
//!
//! let strain = Strain::new(0.05).unwrap();
//! let engineering = engineering_strain(2.0, 2.1).unwrap();
//! let from_change = strain_from_change(2.0, 0.1).unwrap();
//!
//! assert_eq!(strain.percent(), 5.0);
//! assert!((engineering - 0.05).abs() < 1.0e-12);
//! assert!((from_change - 0.05).abs() < 1.0e-12);
//! assert_eq!(percent_strain(0.05).unwrap(), 5.0);
//! ```

#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Strain {
    ratio: f64,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum StrainError {
    InvalidStrain,
    InvalidOriginalLength,
    InvalidFinalLength,
    InvalidChangeInLength,
}

fn validate_finite(value: f64, error: StrainError) -> Result<f64, StrainError> {
    if !value.is_finite() {
        Err(error)
    } else {
        Ok(value)
    }
}

fn validate_original_length(value: f64) -> Result<f64, StrainError> {
    if !value.is_finite() || value <= 0.0 {
        Err(StrainError::InvalidOriginalLength)
    } else {
        Ok(value)
    }
}

impl Strain {
    pub fn new(ratio: f64) -> Result<Self, StrainError> {
        Ok(Self {
            ratio: validate_finite(ratio, StrainError::InvalidStrain)?,
        })
    }

    #[must_use]
    pub fn ratio(&self) -> f64 {
        self.ratio
    }

    #[must_use]
    pub fn percent(&self) -> f64 {
        self.ratio * 100.0
    }
}

pub fn engineering_strain(original_length_m: f64, final_length_m: f64) -> Result<f64, StrainError> {
    let original_length_m = validate_original_length(original_length_m)?;
    let final_length_m = validate_finite(final_length_m, StrainError::InvalidFinalLength)?;

    Ok((final_length_m - original_length_m) / original_length_m)
}

pub fn strain_from_change(
    original_length_m: f64,
    change_in_length_m: f64,
) -> Result<f64, StrainError> {
    Ok(
        validate_finite(change_in_length_m, StrainError::InvalidChangeInLength)?
            / validate_original_length(original_length_m)?,
    )
}

pub fn percent_strain(strain: f64) -> Result<f64, StrainError> {
    Ok(validate_finite(strain, StrainError::InvalidStrain)? * 100.0)
}

#[cfg(test)]
mod tests {
    use super::{Strain, StrainError, engineering_strain, percent_strain, strain_from_change};

    #[test]
    fn computes_strain_values() {
        let strain = Strain::new(0.05).unwrap();
        let engineering = engineering_strain(2.0, 2.1).unwrap();
        let from_change = strain_from_change(2.0, 0.1).unwrap();

        assert_eq!(strain.ratio(), 0.05);
        assert_eq!(strain.percent(), 5.0);
        assert!((engineering - 0.05).abs() < 1.0e-12);
        assert!((from_change - 0.05).abs() < 1.0e-12);
        assert_eq!(percent_strain(0.05).unwrap(), 5.0);
    }

    #[test]
    fn allows_negative_strain_for_contraction() {
        assert!((engineering_strain(2.0, 1.9).unwrap() + 0.05).abs() < 1.0e-12);
        assert_eq!(Strain::new(-0.02).unwrap().percent(), -2.0);
    }

    #[test]
    fn rejects_invalid_length_and_strain_inputs() {
        assert_eq!(Strain::new(f64::NAN), Err(StrainError::InvalidStrain));
        assert_eq!(
            engineering_strain(0.0, 2.0),
            Err(StrainError::InvalidOriginalLength)
        );
        assert_eq!(
            engineering_strain(2.0, f64::INFINITY),
            Err(StrainError::InvalidFinalLength)
        );
        assert_eq!(
            strain_from_change(-1.0, 0.1),
            Err(StrainError::InvalidOriginalLength)
        );
        assert_eq!(
            percent_strain(f64::INFINITY),
            Err(StrainError::InvalidStrain)
        );
    }
}