EntityInstance

EntityInstance[entity,qualval]

represents an entity whose qualifier qual has value val.

EntityInstance[entity,{qual1val1,qual2val2,}]

represents an entity whose qualifiers quali have values vali.

EntityInstance[entity,quantity]

represents an entity qualified by quantity.

Details

  • Entity expressions can be created by using the interface.
  • A qualifier qual can be a property qualifier of an EntityProperty of entity, a QuantityVariable or a Function argument.
  • If entity[property] returns Function[params,body] with a parameter equal to qual, then the associated value is substituted into body and qual is dropped from params. If no parameters remain then the Function wrapper is removed.

Examples

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Basic Examples  (4)

Represent Ireland in the year 1950:

Return its population on that date:

Specify values for a property that is returned as a pure function:

Specify the same values for multiple properties:

Specify values for properties that contain quantity variables:

Specify the mass of a substance:

Scope  (8)

Property Qualifiers  (2)

Specify the properties in the year 1980 using a qualifier inside a property:

This is equivalent to using an entity instance with unqualified properties:

Inapplicable qualifiers are silently ignored:

Dates  (1)

Date qualifiers in an entity instance can be specified as a rule (in the case of a single qualifier):

As a rule list:

Or as a DateObject:

Pure Function Arguments  (1)

Obtain the variables appearing in solid properties:

The properties are pure functions of the variables:

Specify c to get functions of the remaining variable:

Specify all variables:

Quantity Variable Values  (1)

Get the variables a harmonic oscillator depends on:

Specify quantity variables:

Quantities  (2)

Specify 1 mole of water:

Get its mass:

Compute the mass using the molar mass:

The result is the same:

Specify 50 grams of a croissant:

Get the absolute vitamin A content:

Entity Store  (1)

Register "shape" entities:

Represent a disk of radius 2 meters:

Get the area:

A rectangle with one side specified:

The area is given as a Function of the other side:

Unregister the "shape" entities:

Properties & Relations  (1)

Expressions containing unknown or inapplicable instances are silently ignored:

Expressions containing multiple instances apply only to the applicable ones:

Neat Examples  (1)

Get the equations of motion of a double pendulum:

Choose initial conditions:

Solve the equations:

Plot the time evolution of the two arms:

Animate the double pendulum:

Introduced in 2015
 (10.3)