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implement determinant on 3x3 and 4x4 matrices

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This commit is contained in:
Bill Thiede 2021-07-05 15:27:32 -07:00
parent d6ad12e344
commit 762cd45f63
1 changed files with 50 additions and 3 deletions
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53
rtchallenge/src/matrices.rs
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@ -1,5 +1,5 @@
use std::fmt;
use std::ops::{Add, Div, Index, Mul, Neg, Sub};
use std::ops::{Index, Mul};
use crate::tuples::Tuple;
@ -86,7 +86,7 @@ impl Matrix3x3 {
///
/// # Examples
/// ```
/// use rtchallenge::matrices::{Matrix2x2, Matrix3x3};
/// use rtchallenge::matrices::Matrix3x3;
///
/// let a = Matrix3x3::new([3., 5., 0.], [2., -1., -7.], [6., -1., 5.]);
/// let b = a.submatrix(1, 0);
@ -101,7 +101,7 @@ impl Matrix3x3 {
///
/// # Examples
/// ```
/// use rtchallenge::matrices::{Matrix2x2, Matrix3x3};
/// use rtchallenge::matrices::Matrix3x3;
///
/// let a = Matrix3x3::new([3., 5., 0.], [2., -1., -7.], [6., -1., 5.]);
/// assert_eq!(a.minor(0, 0), -12.);
@ -113,6 +113,22 @@ impl Matrix3x3 {
let negate = if (row + col) % 2 == 0 { 1. } else { -1. };
self.submatrix(row, col).determinant() * negate
}
/// Compute determinant of a 3x3 matrix.
///
/// # Examples
/// ```
/// use rtchallenge::matrices::Matrix3x3;
///
/// let a = Matrix3x3::new([1., 2., 6.], [-5., 8., -4.], [2., 6., 4.]);
/// assert_eq!(a.cofactor(0, 0), 56.);
/// assert_eq!(a.cofactor(0, 1), 12.);
/// assert_eq!(a.cofactor(0, 2), -46.);
/// assert_eq!(a.determinant(), -196.);
/// ```
pub fn determinant(&self) -> f32 {
(0..3).map(|i| self.cofactor(0, i) * self[(0, i)]).sum()
}
}
impl Index<(usize, usize)> for Matrix3x3 {
type Output = f32;
@ -333,6 +349,37 @@ impl Matrix4x4 {
];
Matrix3x3 { m }
}
/// Compute minor of a 4x4 matrix.
pub fn minor(&self, row: usize, col: usize) -> f32 {
self.submatrix(row, col).determinant()
}
/// Compute cofactor of a 4x4 matrix.
pub fn cofactor(&self, row: usize, col: usize) -> f32 {
let negate = if (row + col) % 2 == 0 { 1. } else { -1. };
self.submatrix(row, col).determinant() * negate
}
/// Compute determinant of a 4x4 matrix.
///
/// # Examples
/// ```
/// use rtchallenge::matrices::Matrix4x4;
///
/// let a = Matrix4x4::new(
/// [-2., -8., 3., 5.],
/// [-3., 1., 7., 3.],
/// [1., 2., -9., 6.],
/// [-6., 7., 7., -9.],
/// );
/// assert_eq!(a.cofactor(0, 0), 690.);
/// assert_eq!(a.cofactor(0, 1), 447.);
/// assert_eq!(a.cofactor(0, 2), 210.);
/// assert_eq!(a.cofactor(0, 3), 51.);
/// assert_eq!(a.determinant(), -4071.);
/// ```
pub fn determinant(&self) -> f32 {
(0..4).map(|i| self.cofactor(0, i) * self[(0, i)]).sum()
}
}
impl fmt::Debug for Matrix4x4 {