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EntityInstance—Wolfram Documentation

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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
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Property Qualifiers  
Dates  
Pure Function Arguments  
Quantity Variable Values  
Quantities  
Entity Store  
Properties & Relations  
Neat Examples  
See Also
Related Guides
Related Links
History
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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:

Wolfram Language code: EntityInstance[Entity["Country", "Ireland"], "Date" -> 1950]

Return its population on that date:

Wolfram Language code: EntityValue[%, "Population"]

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

Wolfram Language code: Entity["Solid", "HalfTorus"]["SurfaceArea"]
Wolfram Language code: EntityValue[ EntityInstance[Entity["Solid", "HalfTorus"], { -> 1,  -> 2}], "SurfaceArea" ]

Specify the same values for multiple properties:

Wolfram Language code: EntityValue[ EntityInstance[Entity["Solid", "Ball"],  -> 1], {"SurfaceArea", "Volume"} ]

Specify values for properties that contain quantity variables:

Wolfram Language code: EntityValue[ EntityInstance[Entity["PhysicalSystem", "HarmonicOscillator1D"], ω -> Quantity[1, "Radians"/"Seconds"]], {"Lagrangian", "EquationsOfMotion"}, "PropertyAssociation" ]

Specify the mass of a substance:

Wolfram Language code: EntityValue[EntityInstance[Entity["Chemical", "MolecularOxygen"], Quantity[1, "Kilograms"]], "AbsoluteVolume"]

Scope  (8)

Property Qualifiers  (2)

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

Wolfram Language code: EntityValue[Entity["Country", "Spain"], {EntityProperty["Country", "Population", "Date" -> 1980], EntityProperty["Country", "PopulationGrowth", "Date" -> 1980]}]

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

Wolfram Language code: EntityValue[EntityInstance[Entity["Country", "Spain"], "Date" -> 1980], {EntityProperty["Country", "Population"], EntityProperty["Country", "PopulationGrowth"]}]

Inapplicable qualifiers are silently ignored:

Wolfram Language code: EntityValue[EntityInstance[Entity["Country", "Spain"], "Date" -> 1980], "Name"]

Dates  (1)

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

Wolfram Language code: EntityValue[EntityInstance[Entity["Country", "Ireland"], "Date" -> 1950], "Population"]

As a rule list:

Wolfram Language code: EntityValue[EntityInstance[Entity["Country", "Ireland"], {"Date" -> 1950}], "Population"]

Or as a DateObject:

Wolfram Language code: EntityValue[EntityInstance[Entity["Country", "Ireland"], DateObject[{1950}]], "Population"]

Pure Function Arguments  (1)

Obtain the variables appearing in solid properties:

Wolfram Language code: Entity["Solid", "HalfTorus"][EntityProperty["Solid", "Variables"]]

The properties are pure functions of the variables:

Wolfram Language code: Entity["Solid", "HalfTorus"][{EntityProperty["Solid", "Centroid"], EntityProperty["Solid", "SurfaceArea"], EntityProperty["Solid", "Inequalities"]}]

Specify c to get functions of the remaining variable:

Wolfram Language code: EntityValue[EntityInstance[Entity["Solid", "HalfTorus"], { -> 10}], {EntityProperty["Solid", "Centroid"], EntityProperty["Solid", "SurfaceArea"], EntityProperty["Solid", "Inequalities"]}]

Specify all variables:

Wolfram Language code: EntityValue[EntityInstance[Entity["Solid", "HalfTorus"], { -> 10,  -> 2}], {EntityProperty["Solid", "Centroid"], EntityProperty["Solid", "SurfaceArea"], EntityProperty["Solid", "Inequalities"]}]

Quantity Variable Values  (1)

Get the variables a harmonic oscillator depends on:

Wolfram Language code: Entity["PhysicalSystem", "HarmonicOscillator1D"][EntityProperty["PhysicalSystem", "SystemVariables"]]

Specify quantity variables:

Wolfram Language code: EntityValue[EntityInstance[Entity["PhysicalSystem", "HarmonicOscillator1D"], {QuantityVariable["m", "Mass"] -> 1, QuantityVariable["ω", "AngularFrequency"] -> 1}], "EquationsOfMotionSolution"]

Quantities  (2)

Specify 1 mole of water:

Wolfram Language code: EntityInstance[Entity["Chemical", "Water"], Quantity[1, "Moles"]]

Get its mass:

Wolfram Language code: EntityValue[%, "AbsoluteMass"]

Compute the mass using the molar mass:

Wolfram Language code: Entity["Chemical", "Water"][EntityProperty["Chemical", "MolarMass"]]Quantity[1, "Moles"]

The result is the same:

Wolfram Language code: % == %%

Specify 50 grams of a croissant:

Wolfram Language code: EntityInstance[ Entity["Food", { "FoodType" -> Entity["FoodType", "Croissant"], "RelativeWaterContent" -> Quantity[Interval[{0, 0.5}], "Grams" / "Grams"] }], Quantity[50, "Grams"] ]

Get the absolute vitamin A content:

Wolfram Language code: %["AbsoluteVitaminAContent"]

Entity Store  (1)

Register "shape" entities:

Wolfram Language code: EntityRegister[EntityStore["shape" -> <| "Entities" -> <| "rectangle" -> <|"variables" -> {, }, "area" -> Function[{, },  * ]|>, "disk" -> <|"variables" -> {}, "area" -> Function[, π *  ^ 2]|> |> |>]]

Represent a disk of radius 2 meters:

Wolfram Language code: EntityInstance[Entity["shape", "disk"],  -> Quantity[2, "Meters"]]

Get the area:

Wolfram Language code: %["area"]

A rectangle with one side specified:

Wolfram Language code: EntityInstance[Entity["shape", "rectangle"],  -> Quantity[9, "Centimeters"]]

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

Wolfram Language code: %["area"]

Unregister the "shape" entities:

Wolfram Language code: EntityUnregister["shape"]

Properties & Relations  (1)

Expressions containing unknown or inapplicable instances are silently ignored:

Wolfram Language code: EntityValue[ Entity["Solid", "HalfTorus"], "SurfaceArea" ]
Wolfram Language code: EntityValue[ EntityInstance[Entity["Solid", "HalfTorus"], {"blah" -> 2}], "SurfaceArea" ]

Expressions containing multiple instances apply only to the applicable ones:

Wolfram Language code: EntityValue[ EntityInstance[Entity["Solid", "HalfTorus"], {"blah" -> 2,  -> 1}], "SurfaceArea" ]

Neat Examples  (1)

Get the equations of motion of a double pendulum:

Wolfram Language code: eqn = EntityValue[ EntityInstance[Entity["PhysicalSystem", "DoublePendulum"], {Subscript[l, 1] -> 1, Subscript[m, 1] -> 1, Subscript[l, 2] -> 1, Subscript[m, 2] -> 1, g -> 9.81}], "EquationsOfMotion" ]

Choose initial conditions:

Wolfram Language code: theta10 = 0.7; theta20 = 0;

Solve the equations:

Wolfram Language code: {theta1sol, theta2sol} = NDSolveValue[ Join[ eqn /. {Subscript[θ, 1] -> theta1, Subscript[θ, 2] -> theta2}, { theta1[0] == theta10, theta1'[0] == 0, theta2[0] == theta20, theta2'[0] == 0 } ], {theta1, theta2}, {t, 0, 10} ]

Plot the time evolution of the two arms:

Wolfram Language code: Plot[{theta1sol[t], theta2sol[t]}, {t, 0, 10}]

Animate the double pendulum:

Wolfram Language code: Animate[ Graphics[{ Disk[{0, 0}, 0.1], With[{p1 = RotationMatrix[theta1sol[t]].{0, -1}}, { Line[{{0, 0}, p1}], Disk[p1, 0.1], With[{p2 = p1 + RotationMatrix[theta2sol[t]].{0, -1}}, { Line[{p1, p2}], Disk[p2, 0.1] }] }] }, PlotRange -> {{-3, 3}, {-3, 1}} ], {t, 0, 10}, SaveDefinitions -> True ]
Wolfram Research (2015), EntityInstance, Wolfram Language function, https://reference.wolfram.com/language/ref/EntityInstance.html.

Text

Wolfram Research (2015), EntityInstance, Wolfram Language function, https://reference.wolfram.com/language/ref/EntityInstance.html.

CMS

Wolfram Language. 2015. "EntityInstance." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/EntityInstance.html.

APA

Wolfram Language. (2015). EntityInstance. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/EntityInstance.html

BibTeX

@misc{reference.wolfram_2026_entityinstance, author="Wolfram Research", title="{EntityInstance}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/EntityInstance.html}", note=[Accessed: 14-November-2026]}

BibLaTeX

@online{reference.wolfram_2026_entityinstance, organization={Wolfram Research}, title={EntityInstance}, year={2015}, url={https://reference.wolfram.com/language/ref/EntityInstance.html}, note=[Accessed: 14-November-2026]}