Enum Expr 

pub enum Expr {
    Const(Number),
    Var(usize),
    Binary(BinOp, Box<Expr>, Box<Expr>),
    Unary(UnaryOp, Box<Expr>),
    Sum(Vec<Expr>),
    Cse(Rc<Expr>),
    Funcall {
        id: usize,
        args: Vec<FuncallArg>,
    },
    Compare(CmpOp, Box<Expr>, Box<Expr>),
    And(Box<Expr>, Box<Expr>),
    Or(Box<Expr>, Box<Expr>),
    Not(Box<Expr>),
    Cond {
        cond: Box<Expr>,
        then_: Box<Expr>,
        else_: Box<Expr>,
    },
    MinList(Vec<Expr>),
    MaxList(Vec<Expr>),
}

Variants

Const(Number)

Numeric constant.

Var(usize)

Variable reference (0-based index into x).

Binary(BinOp, Box<Expr>, Box<Expr>)

Binary op: args = [lhs, rhs].

Unary(UnaryOp, Box<Expr>)

Unary op.

Sum(Vec<Expr>)

n-ary sum (opcode o54 — variadic; we may emit it from o0 folding optimization, but the parser treats o0 as binary).

Cse(Rc<Expr>)

Reference to a common subexpression (.nl V segment). The payload is a shared body; many references to the same CSE share one Rc, so the parsed problem is a DAG. Walking through Cse is mathematically equivalent to inlining the body at each occurrence (every reference is an independent occurrence in the chain rule), so eval/grad/collect_vars just recurse into the inner Expr.

Funcall

AMPL imported (external) function call. id matches an entry in NlProblem.imported_funcs; resolution to a live shared library happens when the tape is built (see nl_external::ExternalResolver).

Fields

id: usize

args: Vec<FuncallArg>

Compare(CmpOp, Box<Expr>, Box<Expr>)

Relational comparison (o22/o23/o24/o28/o29/o30). Evaluates to 1.0 when the comparison holds, else 0.0. The result is piecewise-constant, so it has zero derivative everywhere (the kink at equality is ignored — standard subgradient-free treatment, matching ASL).

And(Box<Expr>, Box<Expr>)

Logical AND (o21). 1.0 iff both operands are nonzero. Zero derivative (piecewise constant).

Or(Box<Expr>, Box<Expr>)

Logical OR (o20). 1.0 iff either operand is nonzero. Zero derivative (piecewise constant).

Not(Box<Expr>)

Logical NOT (o34). 1.0 iff the operand is zero. Zero derivative (piecewise constant).

Cond

if-then-else (o35 OPIFnl). Evaluates cond; when it is nonzero the value and all derivatives flow through then_, otherwise through else_. The branch switch is a non-smooth event the derivative ignores (it differentiates only the active branch), exactly as ASL/IPOPT does for if.

Fields

cond: Box<Expr>

then_: Box<Expr>

else_: Box<Expr>

MinList(Vec<Expr>)

n-ary minimum (o11 MINLIST). Value is the smallest operand. Piecewise linear: the derivative flows through whichever operand is currently smallest (a subgradient; ties resolve to the first such operand), and the second derivative is identically zero — the standard AD treatment for min/max, matching ASL/IPOPT.

MaxList(Vec<Expr>)

n-ary maximum (o12 MAXLIST). Value is the largest operand; derivative routing mirrors Expr::MinList.

Trait Implementations

impl Clone for Expr

fn clone(&self) -> Expr

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Expr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.