numopt 0.2.1

Numerical optimization problem abstractions, solver interfaces, and modeling tools.
Documentation 
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//! Cosine function.

use std::fmt;
use std::rc::Rc;
use std::collections::HashMap;

use crate::model::node::Node;
use crate::model::node_base::NodeBase;
use crate::model::node_std::{NodeStd, NodeStdProp};
use crate::model::node_func::NodeFunc;
use crate::model::constant::ConstantScalar;

/// Cosine function.
pub struct FunctionCos {
    arg: Node
}

impl FunctionCos {

    /// Creates new cosine expression node.
    pub fn new(arg: Node) -> Node {
        Node::FunctionCos(Rc::new(
            Self {
                arg: arg,
            }
        ))
    }
}

impl NodeBase for FunctionCos {

    fn arguments(&self) -> Vec<&Node> {
        vec![&self.arg]
    }

    fn partial(&self, arg: &Node) -> Node { 
        if self.arg == *arg {
            return -&self.arg.sin();
        }
        else {
            return ConstantScalar::new(0.);
        }
    }

    fn evaluate(&self, var_values: &HashMap<&Node, f64>) -> f64 { 
        self.arg.evaluate(var_values).cos()
    }
}

impl NodeStd for FunctionCos {

    fn std_properties(&self) -> NodeStdProp {
        let mut p = self.arg.std_properties();
        p.affine = false;
        p
    }
}

impl<'a> fmt::Display for FunctionCos {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "cos({})", self.arg)
    }
}

#[cfg(test)]
mod tests {

    use crate::model::node_base::NodeBase;
    use crate::model::node_std::NodeStd;
    use crate::model::node_func::NodeFunc;
    use crate::model::node_diff::NodeDiff;
    use crate::model::variable::VariableScalar;

    #[test]
    fn cos_partial() {

        let x = VariableScalar::new_continuous("x");
        let y = VariableScalar::new_continuous("Y");

        let z = x.cos();
        
        let z1 = z.partial(&x);
        assert_eq!(format!("{}", z1), "-1*sin(x)");
        
        let z2 = z.partial(&y);
        assert!(z2.is_constant_with_value(0.));
    }

    #[test]
    fn cos_derivative() {

        let x = VariableScalar::new_continuous("x");
        let y = VariableScalar::new_continuous("y");

        let z1 = x.cos();
        let z1x = z1.derivative(&x);
        let z1y = z1.derivative(&y);
        assert_eq!(format!("{}", z1x), "-1*sin(x)");
        assert!(z1y.is_constant_with_value(0.));

        let z2 = (5.*&x + 3.*&y).cos();
        let z2x = z2.derivative(&x);
        let z2y = z2.derivative(&y);
        assert_eq!(format!("{}", z2x), "-1*sin(5*x + 3*y)*5");
        assert_eq!(format!("{}", z2y), "-1*sin(5*x + 3*y)*3");
    }
    
    #[test]
    fn cos_std_properties() {

        let x = VariableScalar::new_continuous("x");
        let y = VariableScalar::new_continuous("y");

        let z1 = &x.cos();
        let p1 = z1.std_properties();
        assert!(!p1.affine);
        assert_eq!(p1.a.len(), 1);
        assert!(p1.a.contains_key(&x));

        let z2 = 3.*(&x + &y).cos();
        let p2 = z2.std_properties();
        assert!(!p2.affine);
        assert_eq!(p2.a.len(), 2);
        assert!(p2.a.contains_key(&x));
        assert!(p2.a.contains_key(&y));
    }
}