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```
```// Copyright 2018-2020 argmin developers
//
// copied, modified, or distributed except according to those terms.

//! Steepest Descent method
//!
//! [SteepestDescent](struct.SteepestDescent.html)
//!
//! # References:
//!
//! [0] Jorge Nocedal and Stephen J. Wright (2006). Numerical Optimization.
//! Springer. ISBN 0-387-30303-0.

use crate::prelude::*;
use serde::{Deserialize, Serialize};

/// Steepest descent iteratively takes steps in the direction of the strongest negative gradient.
/// In each iteration, a line search is employed to obtain an appropriate step length.
///
/// [Example](https://github.com/argmin-rs/argmin/blob/master/examples/steepestdescent.rs)
///
/// # References:
///
/// [0] Jorge Nocedal and Stephen J. Wright (2006). Numerical Optimization.
/// Springer. ISBN 0-387-30303-0.
#[derive(Clone, Serialize, Deserialize)]
pub struct SteepestDescent<L> {
/// line search
linesearch: L,
}

impl<L> SteepestDescent<L> {
/// Constructor
pub fn new(linesearch: L) -> Self {
SteepestDescent { linesearch }
}
}

impl<O, L, F> Solver<O> for SteepestDescent<L>
where
O: ArgminOp<Output = F, Float = F>,
O::Param: Clone
+ Default
+ Serialize
+ ArgminSub<O::Param, O::Param>
+ ArgminDot<O::Param, O::Float>
+ ArgminMul<O::Float, O::Param>
+ ArgminSub<O::Param, O::Param>
+ ArgminNorm<O::Float>,
O::Hessian: Default,
L: Clone + ArgminLineSearch<O::Param, O::Float> + Solver<OpWrapper<O>>,
F: ArgminFloat,
{
const NAME: &'static str = "Steepest Descent";

fn next_iter(
&mut self,
op: &mut OpWrapper<O>,
state: &IterState<O>,
) -> Result<ArgminIterData<O>, Error> {
let param_new = state.get_param();
let new_cost = op.apply(&param_new)?;

self.linesearch

// Run solver
let ArgminResult {
operator: line_op,
state:
IterState {
param: next_param,
cost: next_cost,
..
},
} = Executor::new(
OpWrapper::new_from_wrapper(op),
self.linesearch.clone(),
param_new,
)
.cost(new_cost)
.ctrlc(false)
.run()?;

// Get back operator and function evaluation counts
op.consume_op(line_op);

Ok(ArgminIterData::new().param(next_param).cost(next_cost))
}
}

#[cfg(test)]
mod tests {
use super::*;
use crate::solver::linesearch::MoreThuenteLineSearch;
use crate::test_trait_impl;

test_trait_impl!(
steepest_descent,
SteepestDescent<MoreThuenteLineSearch<Vec<f64>, f64>>
);
}
```