Parameters, variables, constraints and the objective#

These four blocks carry the math, and given: names what the math reads from another file. Each takes an optional description:, free text that the typeset legend prints.

parameters#

A parameter declares a shape. The numbers arrive by name with the data.

dimensions:
  snapshot: { dtype: int }
parameters:
  load:
    dims: [snapshot]
  discount_rate:
    dims: [] # a scalar

The column has to match the dtype:

A null or NaN value is refused when the data is attached. A coordinate with no value has no row. inf and -inf are values.

Only float and int are values. A str parameter is a label and a bool parameter is a mask: each selects rows in a where, and writing either as a coefficient, a term or a divisor is a load error. A 0 or 1 that is meant to be multiplied by is declared dtype: int.

variables#

A variable is what the solver decides. There is one column per coordinate of dims.

dimensions:
  snapshot: { dtype: int }
  generator: { dtype: str }
parameters:
  capacity: { dims: [generator] }
variables:
  dispatch:
    dims: [snapshot, generator]
    where: "capacity > 0"
    bounds:
      lower: 0
      upper: capacity

An open side is null. A bound is never infinite: .inf and -.inf are refused, with null named as the rewrite.

A bound is a name or a number: upper: capacity is accepted, and upper: -rating is refused. Ship the negated column as data.

Equal bounds pin a variable (fix a quantity). A pinned variable is still a variable.

given#

given: holds what this file reads and does not build: data under parameters:, columns under variables:, named expressions under expressions:, and row families under constraints:. It takes those four keys and no other. A file with a given: block loads and prints on its own.

given: parameters#

A given parameter is data this file reads and another file declares.

dimensions:
  snapshot: { dtype: int }
  generator: { dtype: str }
given:
  parameters:
    gen_cost: { dims: [generator], description: what one unit of output costs }
    gen_on: { dims: [generator], dtype: bool }
  variables:
    gen_p: { dims: [snapshot, generator] }
constraints:
  off_units_idle:
    dims: [snapshot, generator]
    where: not gen_on
    expression: gen_p <= 0
objective:
  sense: minimize
  expression: sum(gen_p * gen_cost)

A given parameter is read wherever a parameter is: in an expression, a where and a bound. A name declared under both parameters: and given: parameters: is refused. The typeset legend lists a given parameter under Given.

given: variables#

A given variable is a column this file reads and another file introduces.

dimensions:
  snapshot: { dtype: int }
  port: { dtype: str }
  generator: { dtype: str }
relations:
  gen_port: { key: generator, values: port }
variables:
  gen_p: { dims: [snapshot, generator], bounds: { lower: 0 } }
given:
  variables:
    flow:
      dims: [snapshot, port]
      description: what a port puts into its bus
constraints:
  gen_injects:
    dims: [snapshot, generator]
    expression: at(flow, by=gen_port, over=port, into=generator) == gen_p

There is no bounds and no where. The file that introduces the column owns both.

An expression reads a given variable as it reads any other. A name declared under both variables: and given: variables: is refused. The typeset legend lists a given variable under Given, and prints no domain line for it.

merge folds a given declaration into the declaration of another fragment that introduces the name, so a composed library carries none of them. The folded declaration is the introducer's, and what the reader states has to say the same or less.

Where nothing in this language introduces the column, the program carries the declaration until a host model provides it (what a program does not build).

given: constraints#

A given constraint is a row family that another model builds. This file reads its dual.

dimensions:
  snapshot: { dtype: int }
  bus: { dtype: str }
given:
  constraints:
    balance:
      dims: [snapshot, bus]
      description: the host model clears each bus
expressions:
  price:
    expression: dual(balance)

There is no expression and no sense. dual(name) is the only place a given row family may be named, and the frame gives the reported expression its dimensions. A name declared under both constraints: and given: constraints: is refused.

given: expressions#

A given expression is a named expression this file reads and another file defines.

dimensions:
  snapshot: { dtype: int }
  bus: { dtype: str }
given:
  expressions:
    injection:
      dims: [snapshot, bus]
      description: what the components put into a bus
constraints:
  balance:
    dims: [snapshot, bus]
    expression: injection == 0

There is no body but the term this file adds, if any. This file reads the name as it reads a given variable: a quantity over the frame, of degree one. A where does not read it, because a mask is built before any variable exists. A name declared under both expressions: and given: expressions: is refused. The typeset legend lists a given expression under Given.

merge folds a given expression into the definition of another fragment. The dims are an upper bound: a body that carries a dimension they do not name is refused. A body over fewer dimensions is folded, and the composed spec decides: it refuses a row that would repeat across the missing dimension, and accepts one where another term carries it. The composed spec holds the body to the rules of every place this file reads it: a square of a given expression that is quadratic is refused once folded.

A term a file adds#

term: names the expression this file adds to the name. The term is an ordinary named expression of this file, so it takes cases:, a description and every other field a named expression takes. The file reads the name as the whole sum, alone and composed, and the term is its part of it. A file that only reads the name writes no term.

The name is an expressions: block of one other file. Where that file has nothing of its own to put in, it declares the sum empty: true over a frame, an empty sum, reads it as a column until the terms arrive, and prints its definition as injection = ⋯:

# fleet.yaml adds a term
dimensions:
  snapshot: { dtype: int }
  bus: { dtype: str }
  generator: { dtype: str }
relations:
  gen_bus: { key: generator, values: bus }
variables:
  gen_p: { dims: [snapshot, generator], bounds: { lower: 0 } }
expressions:
  generation:
    description: what the fleet puts into a bus
    expression: sum(gen_p, by=gen_bus, over=generator, into=bus)
given:
  expressions:
    injection:
      dims: [snapshot, bus]
      term: generation

# balance.yaml declares the sum, and adds nothing to it
dimensions:
  snapshot: { dtype: int }
  bus: { dtype: str }
expressions:
  injection:
    dims: [snapshot, bus]
    empty: true
    description: what the components put into a bus
constraints:
  balance:
    dims: [snapshot, bus]
    expression: injection == 0

Each file loads alone. The term names an expression the file declares, and that expression does not read the name it adds to, directly or through another name. It carries no dimension the entry does not state, and it is held to degree two, as what reads the sum is. All of this is checked at load. The typeset legend lists the entry under Given and names the term, and the math prints the term under Definitions as its own line.

merge writes the name's body as the owner's body, if it has one, plus every term by its name, in the order the files are given in, and keeps each term as a named expression of the composed spec. An empty sum keeps its frame, so the composed spec holds the terms to it. A term adds to whatever the owner wrote, as a fragment's objective adds to the objective, and a later merge adds to the composed body the same way. The owner does not opt in. A file with a body reads it alone, and the body plus every term once composed; whoever composes the files answers for that sum. A term has to land on an expressions: block another file declares. Terms alone are refused, with the near miss named, since merge fills or extends what a file declared and never invents a name. A body written as cases: is refused, since it is summed as written: name the cased body as its own expression, and define the name as that name. A cased term is added like any other, by its name. The block keeps the owner's description, or takes the first a reader wrote. Two files that both declare the name under expressions: are refused as a collision, and the message names term:.

constraints#

One block is one rule. The name of the block is the name of the constraint.

dimensions:
  snapshot: { dtype: int }
  generator: { dtype: str }
parameters:
  load: { dims: [snapshot] }
variables:
  dispatch: { dims: [snapshot, generator] }
constraints:
  power_balance:
    dims: [snapshot]
    expression: sum(dispatch, over=generator) == load

The dimensions of the expression must equal its dims (how dimensions combine).

At least one side of the comparator carries a variable. A comparison between numbers and parameters alone is refused at load.

dims: [] gives one scalar row. A scalar variable may not carry a where; put the condition on the constraints that use it.

Two regimes of one rule are two blocks, each under its own where: (state a rule that differs by regime).

objective#

The objective is a single block with no name.

dimensions:
  generator: { dtype: str }
parameters:
  cost: { dims: [generator] }
variables:
  dispatch: { dims: [generator] }
objective:
  sense: minimize
  expression: sum(dispatch * cost)

The expression must be scalar. Nothing is summed for you: sum(x * a) + sum(y * b) and sum(x * a + y * b) are both allowed, and they state different objectives.

There is one objective block. To pursue several goals, weight them into one expression.