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use super::Vector;
use crate::to_i32;
extern "C" {
// Scales a vector by a constant
// <https://www.netlib.org/lapack/explore-html/d4/dd0/dscal_8f.html>
fn cblas_dscal(n: i32, alpha: f64, x: *mut f64, incx: i32);
}
/// Scales a vector by a constant
///
/// ```text
/// u := alpha * u
/// ```
///
/// See also: <https://www.netlib.org/lapack/explore-html/d4/dd0/dscal_8f.html>
///
/// # Examples
///
/// ```
/// use russell_lab::{vec_scale, Vector};
///
/// fn main() {
/// let mut u = Vector::from(&[1.0, 2.0, 3.0]);
/// vec_scale(&mut u, 0.5);
/// let correct = "┌ ┐\n\
/// │ 0.5 │\n\
/// │ 1 │\n\
/// │ 1.5 │\n\
/// └ ┘";
/// assert_eq!(format!("{}", u), correct);
/// }
/// ```
pub fn vec_scale(v: &mut Vector, alpha: f64) {
let n_i32: i32 = to_i32(v.dim());
unsafe {
cblas_dscal(n_i32, alpha, v.as_mut_data().as_mut_ptr(), 1);
}
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
#[cfg(test)]
mod tests {
use super::{vec_scale, Vector};
use crate::vec_approx_eq;
#[test]
fn vec_scale_works() {
let mut u = Vector::from(&[6.0, 9.0, 12.0]);
vec_scale(&mut u, 1.0 / 3.0);
let correct = &[2.0, 3.0, 4.0];
vec_approx_eq(&u, correct, 1e-15);
}
}