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Impl new_from_octahedral_alpha in Tensor2 #123

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Jul 23, 2024
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Impl new_from_octahedral_alpha in Tensor2 #123

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187 changes: 173 additions & 14 deletions russell_tensor/src/tensor2.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
use crate::{AsMatrix3x3, Mandel, StrError};
use crate::{IJ_TO_M, IJ_TO_M_SYM, M_TO_IJ, TOL_J2};
use crate::{SQRT_2, SQRT_2_BY_3, SQRT_3, SQRT_3_BY_2, SQRT_6};
use russell_lab::math::PI;
use russell_lab::{Matrix, Vector};
use serde::{Deserialize, Serialize};

Expand Down Expand Up @@ -153,6 +154,47 @@ impl Tensor2 {
Ok(tt)
}

/// Allocates a diagonal Tensor2 from octahedral components (using alpha angle)
///
/// # Input
///
/// * `distance` -- distance from the octahedral plane to the origin: `d = (λ1 + λ2 + λ3) / √3`
/// * `radius` -- radius on the octahedral plane: `r = ‖s‖`
/// * `alpha` -- alpha angle in radians from -π to π
/// * `two_dim` -- 2D instead of 3D?
///
/// The octahedral components and the invariants are related as follows:
///
/// ```text
/// σm = d / √3 → d = σm √3
/// σd = r √3/√2 → r = σd √2/√3 = √2 √J2
/// εv = d √3 → d = εv / √3
/// εd = r √2/√3 → r = εd √3/√2
/// ```
///
/// In matrix form, the diagonal components of the tensor are the principal values `(λ1, λ2, λ3)`:
///
/// ```text
/// ┌ ┐
/// │ λ1 0 0 │
/// │ 0 λ2 0 │
/// │ 0 0 λ3 │
/// └ ┘
/// ```
pub fn new_from_octahedral_alpha(distance: f64, radius: f64, alpha: f64, two_dim: bool) -> Result<Self, StrError> {
if alpha < -PI || alpha > PI {
return Err("alpha must be in -π ≤ alpha ≤ π");
}
let star1 = radius * f64::sin(alpha);
let star2 = distance;
let star3 = radius * f64::cos(alpha);
let mut tt = Tensor2::new_sym(two_dim);
tt.vec[0] = (SQRT_2 * star1 + star2) / SQRT_3;
tt.vec[1] = -star1 / SQRT_6 + star2 / SQRT_3 - star3 / SQRT_2;
tt.vec[2] = -star1 / SQRT_6 + star2 / SQRT_3 + star3 / SQRT_2;
Ok(tt)
}

/// Returns the Mandel representation associated with this Tensor2
pub fn mandel(&self) -> Mandel {
self.mandel
Expand Down Expand Up @@ -1953,7 +1995,7 @@ impl Tensor2 {
#[cfg(test)]
mod tests {
use super::Tensor2;
use crate::{Mandel, SampleTensor2, SamplesTensor2, IDENTITY2, SQRT_2, SQRT_2_BY_3, SQRT_3, SQRT_3_BY_2};
use crate::{Mandel, SampleTensor2, SamplesTensor2, IDENTITY2, SQRT_2, SQRT_2_BY_3, SQRT_3, SQRT_3_BY_2, SQRT_6};
use russell_lab::{approx_eq, mat_approx_eq, mat_mat_mul, math::PI, vec_approx_eq, Matrix, Vector};

#[test]
Expand Down Expand Up @@ -2677,10 +2719,7 @@ mod tests {
// symmetric 3D
let mut tt = Tensor2::new(Mandel::Symmetric);
tt.vec.fill(NOISE);
tt.set_mandel_vector(
2.0,
&[1.0, 2.0, 3.0, 4.0 * SQRT_2, 5.0 * SQRT_2, 6.0 * SQRT_2],
);
tt.set_mandel_vector(2.0, &[1.0, 2.0, 3.0, 4.0 * SQRT_2, 5.0 * SQRT_2, 6.0 * SQRT_2]);
let correct = &[[2.0, 8.0, 12.0], [8.0, 4.0, 10.0], [12.0, 10.0, 6.0]];
mat_approx_eq(&tt.as_matrix(), correct, 1e-14);

Expand Down Expand Up @@ -3480,34 +3519,154 @@ mod tests {
}

#[test]
fn new_from_oct_invariants_works() {
fn new_from_octahedral_works() {
assert_eq!(
Tensor2::new_from_octahedral(0.0, 0.0, -2.0, true).err(),
Some("lode invariant must be in -1 ≤ lode ≤ 1")
);

let (sigma_m, sigma_d) = (1.0, 3.0);
let (distance, radius) = (sigma_m * SQRT_3, sigma_d * SQRT_2_BY_3);

let t1 = Tensor2::new_from_octahedral(distance, radius, 1.0, true).unwrap();
let t2 = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 2.0, true).unwrap();
assert_eq!(t1.vec.dim(), 4);
approx_eq(t1.vec[0], 3.0, 1e-15);
approx_eq(t1.vec[1], 0.0, 1e-15);
approx_eq(t1.vec[2], 0.0, 1e-15);
assert_eq!(t1.vec[3], 0.0);
vec_approx_eq(&t1.vec, &t2.vec, 1e-15);

let t1 = Tensor2::new_from_octahedral(distance, radius, 0.0, true).unwrap();
let t2 = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 3.0, true).unwrap();
assert_eq!(t1.vec.dim(), 4);
approx_eq(t1.vec[0], 1.0 + SQRT_3, 1e-15);
approx_eq(t1.vec[1], 1.0 - SQRT_3, 1e-15);
approx_eq(t1.vec[2], 1.0, 1e-15);
assert_eq!(t1.vec[3], 0.0);
vec_approx_eq(&t1.vec, &t2.vec, 1e-15);

let t1 = Tensor2::new_from_octahedral(distance, radius, -1.0, true).unwrap();
let t2 = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 6.0, true).unwrap();
assert_eq!(t1.vec.dim(), 4);
approx_eq(t1.vec[0], 2.0, 1e-15);
approx_eq(t1.vec[1], -1.0, 1e-15);
approx_eq(t1.vec[2], 2.0, 1e-15);
assert_eq!(t1.vec[3], 0.0);
vec_approx_eq(&t1.vec, &t2.vec, 1e-15);
}

#[test]
fn new_from_octahedral_alpha_works() {
assert_eq!(
Tensor2::new_from_octahedral(0.0, 0.0, -2.0, true).err(),
Some("lode invariant must be in -1 ≤ lode ≤ 1")
Tensor2::new_from_octahedral_alpha(0.0, 0.0, -2.0 * PI, true).err(),
Some("alpha must be in -π ≤ alpha ≤ π")
);

let tt = Tensor2::new_from_octahedral(distance, radius, 1.0, true).unwrap();
let (distance, radius) = (SQRT_3, SQRT_6);

// 0 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, 0.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0, 1e-15);
approx_eq(tt.vec[1], 1.0 - SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0 + SQRT_3, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// 30 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 6.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 2.0, 1e-15);
approx_eq(tt.vec[1], -1.0, 1e-15);
approx_eq(tt.vec[2], 2.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// 60 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 3.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0 + SQRT_3, 1e-15);
approx_eq(tt.vec[1], 1.0 - SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// 90 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, PI / 2.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 3.0, 1e-15);
approx_eq(tt.vec[1], 0.0, 1e-15);
approx_eq(tt.vec[2], 0.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

let tt = Tensor2::new_from_octahedral(distance, radius, 0.0, true).unwrap();
// 120 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, 2.0 * PI / 3.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0 + SQRT_3, 1e-15);
approx_eq(tt.vec[1], 1.0 - SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0, 1e-15);
approx_eq(tt.vec[1], 1.0, 1e-15);
approx_eq(tt.vec[2], 1.0 - SQRT_3, 1e-15);
assert_eq!(tt.vec[3], 0.0);

let tt = Tensor2::new_from_octahedral(distance, radius, -1.0, true).unwrap();
// 150 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, 5.0 * PI / 6.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 2.0, 1e-15);
approx_eq(tt.vec[1], -1.0, 1e-15);
approx_eq(tt.vec[1], 2.0, 1e-15);
approx_eq(tt.vec[2], -1.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// 180 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, PI, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0, 1e-15);
approx_eq(tt.vec[1], 1.0 + SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0 - SQRT_3, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -180 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -PI, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0, 1e-15);
approx_eq(tt.vec[1], 1.0 + SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0 - SQRT_3, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -150 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -5.0 * PI / 6.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 0.0, 1e-15);
approx_eq(tt.vec[1], 3.0, 1e-15);
approx_eq(tt.vec[2], 0.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -120 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -2.0 * PI / 3.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0 - SQRT_3, 1e-15);
approx_eq(tt.vec[1], 1.0 + SQRT_3, 1e-15);
approx_eq(tt.vec[2], 1.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -90 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -PI / 2.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], -1.0, 1e-15);
approx_eq(tt.vec[1], 2.0, 1e-15);
approx_eq(tt.vec[2], 2.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -60 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -PI / 3.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 1.0 - SQRT_3, 1e-15);
approx_eq(tt.vec[1], 1.0, 1e-15);
approx_eq(tt.vec[2], 1.0 + SQRT_3, 1e-15);
assert_eq!(tt.vec[3], 0.0);

// -30 degrees
let tt = Tensor2::new_from_octahedral_alpha(distance, radius, -PI / 6.0, true).unwrap();
assert_eq!(tt.vec.dim(), 4);
approx_eq(tt.vec[0], 0.0, 1e-15);
approx_eq(tt.vec[1], 0.0, 1e-15);
approx_eq(tt.vec[2], 3.0, 1e-15);
assert_eq!(tt.vec[3], 0.0);
}
}