# thermalIC

Set initial conditions or initial guess for a thermal model

**Domain-specific heat transfer workflow is not recommended. New features might not be
compatible with this workflow. For help migrating your existing code to the unified
finite element workflow, see Migration from Domain-Specific to Unified Workflow.**

## Syntax

## Description

`thermalIC(`

sets initial temperature or initial guess for temperature to the entire
geometry.`thermalmodel`

,`T0`

)

`thermalIC(`

sets initial temperature or initial guess for temperature to a particular geometry
region.`thermalmodel`

,`T0`

,`RegionType`

,`RegionID`

)

`thermalIC(`

sets initial temperature or initial guess for temperature using the solution
`thermalmodel`

,`Tresults`

)`Tresults`

from a previous thermal analysis on the same
geometry and mesh. If `Tresults`

is obtained by solving a
transient thermal problem, `thermalIC`

uses the solution
`Tresults`

for the last time-step.

`thermalIC(`

sets initial temperature or initial guess for temperature using the solution
`thermalmodel`

,`Tresults`

,`iT`

)`Tresults`

for the time-step `iT`

from a
previous thermal analysis on the same geometry and mesh.

,
for any previous syntax, returns a handle to the thermal initial conditions
object.`thermalIC`

= thermalIC(___)

## Examples

### Constant Initial Temperature

Create a thermal model, import geometry, and set the initial temperature to 0 on the entire geometry.

thermalModel = createpde("thermal","transient"); geometryFromEdges(thermalModel,@lshapeg); thermalIC(thermalModel,0)

ans = GeometricThermalICs with properties: RegionType: 'face' RegionID: [1 2 3] InitialTemperature: 0

### Different Initial Temperatures on Subdomains

Set different initial conditions on each portion of the L-shaped membrane geometry.

Create a model and include a 2-D geometry.

thermalModel = createpde("thermal","transient"); geometryFromEdges(thermalModel,@lshapeg); pdegplot(thermalModel,"FaceLabels","on") axis equal ylim([-1.1 1.1])

Set initial conditions.

`thermalIC(thermalModel,0,"Face",1)`

ans = GeometricThermalICs with properties: RegionType: 'face' RegionID: 1 InitialTemperature: 0

`thermalIC(thermalModel,10,"Face",2)`

ans = GeometricThermalICs with properties: RegionType: 'face' RegionID: 2 InitialTemperature: 10

`thermalIC(thermalModel,75,"Face",3)`

ans = GeometricThermalICs with properties: RegionType: 'face' RegionID: 3 InitialTemperature: 75

### Nonconstant Initial Temperature

Use a function handle to specify an initial temperature that depends on coordinates.

Create a thermal model for transient analysis and include the geometry. The geometry is a rod with a circular cross section. The 2-D model is a rectangular strip whose *y*-dimension extends from the axis of symmetry to the outer surface, and whose *x*-dimension extends over the actual length of the rod.

thermalmodel = createpde("thermal","transient"); g = decsg([3 4 -1.5 1.5 1.5 -1.5 0 0 .2 .2]'); geometryFromEdges(thermalmodel,g);

Set the initial temperature in the rod to be dependent on the *y*-coordinate, for example, ${10}^{3}\left(0.2-{\mathit{y}}^{2}\right)$.

T0 = @(location)10^3*(0.2 - location.y.^2); thermalIC(thermalmodel,T0)

ans = GeometricThermalICs with properties: RegionType: 'face' RegionID: 1 InitialTemperature: @(location)10^3*(0.2-location.y.^2)

### Initial Condition as Previously Obtained Solution

Create a thermal model and include a square geometry.

thermalmodel = createpde("thermal","transient"); geometryFromEdges(thermalmodel,@squareg); pdegplot(thermalmodel,"FaceLabels","on") ylim([-1.1,1.1]) axis equal

Specify material properties and internal heat source, and set boundary conditions and initial conditions.

thermalProperties(thermalmodel, ... "ThermalConductivity",40,... "MassDensity",7800,... "SpecificHeat",500); internalHeatSource(thermalmodel,2); thermalBC(thermalmodel,"Edge",[1,3], ... "Temperature",100); thermalIC(thermalmodel,0);

Generate mesh, solve the problem, and plot the solution.

```
generateMesh(thermalmodel);
tlist = 0:10:100;
result1 = solve(thermalmodel,tlist);
pdeplot(thermalmodel,"XYData",result1.Temperature(:,end))
```

Now, resume the analysis and solve the problem for times from 100 to 1000 seconds. Use the previously obtained solution for 100 seconds as an initial condition. Since 10 seconds is the last element in `tlist`

, you do not need to specify the solution time index. By default, `thermalIC`

uses the last solution index.

thermalIC(thermalmodel,result1);

Solve the problem and plot the solution.

```
result2 = solve(thermalmodel,100:100:1000);
pdeplot(thermalmodel,"XYData",result2.Temperature(:,end))
```

To use the previously obtained solution for a particular solution time instead of the last one, specify the solution time index as a third parameter of `thermalIC`

. For example, use the solution at time 50 seconds, which is the 6th element in `tlist`

.

tlist(6)

ans = 50

thermalIC(thermalmodel,result1,6);

```
result2 = solve(thermalmodel,50:100:1000);
pdeplot(thermalmodel,"XYData",result2.Temperature(:,end))
```

## Input Arguments

`thermalmodel`

— Thermal model

`ThermalModel`

object

Thermal model, specified as a `ThermalModel`

object.
The model contains the geometry, mesh, thermal properties of the material,
internal heat source, boundary conditions, and initial conditions.

**Example: **`thermalmodel = createpde("thermal","steadystate")`

`T0`

— Initial temperature or initial guess for temperature

number | function handle

Initial temperature or initial guess for temperature, specified as a number or a function handle. Use a function handle to specify spatially varying initial temperature. For details, see More About.

**Data Types: **`double`

| `function_handle`

`RegionType`

— Geometric region type

`"Vertex"`

| `"Edge"`

| `"Face"`

| `"Cell"`

for a 3-D model only

Geometric region type, specified as `"Vertex"`

,
`"Edge"`

, `"Face"`

, or
`"Cell"`

for a 3-D model. For a 2-D model, use
`"Vertex"`

, `"Edge"`

, or
`"Face"`

.

**Example: **`thermalIC(thermalmodel,10,"Face",1)`

**Data Types: **`char`

| `string`

`RegionID`

— Geometric region ID

vector of positive integers

Geometric region ID, specified as a vector of positive integers. Find the
region IDs by using `pdegplot`

.

**Example: **`thermalIC(thermalmodel,10,"Edge",2:5)`

**Data Types: **`double`

`Tresults`

— Thermal model solution

`SteadyStateThermalResults`

object | `TransientThermalResults`

object

Thermal model solution, specified as a
`SteadyStateThermalResults`

or
`TransientThermalResults`

object. Create
`Tresults`

by using `solve`

.

`iT`

— Time index

positive integer

Time index, specified as a positive integer.

**Example: **`thermalIC(thermalmodel,Tresults,21)`

**Data Types: **`double`

## Output Arguments

`thermalIC`

— Handle to initial condition

`GeometricThermalICs`

object | `NodalThermalICs`

object

Handle to initial condition, returned as a
`GeometricThermalICs`

or
`NodalThermalICs`

object. See GeometricThermalICs Properties
and NodalThermalICs Properties.

`thermalIC`

associates the thermal initial condition with
the geometric region in the case of a geometric assignment, or the nodes in
the case of a results-based assignment.

## More About

### Specifying Nonconstant Parameters of a Thermal Model

Use a function handle to specify these thermal parameters when they depend on space, temperature, and time:

Thermal conductivity of the material

Mass density of the material

Specific heat of the material

Internal heat source

Temperature on the boundary

Heat flux through the boundary

Convection coefficient on the boundary

Radiation emissivity coefficient on the boundary

Initial temperature (can depend on space only)

For example, use function handles to specify the thermal conductivity, internal heat source, convection coefficient, and initial temperature for this model.

thermalProperties(model,"ThermalConductivity", ... @myfunConductivity) internalHeatSource(model,"Face",2,@myfunHeatSource) thermalBC(model,"Edge",[3,4], ... "ConvectionCoefficient",@myfunBC, ... "AmbientTemperature",27) thermalIC(model,@myfunIC)

For all parameters, except the initial temperature, the function must be of the form:

`function thermalVal = myfun(location,state)`

For the initial temperature the function must be of the form:

`function thermalVal = myfun(location)`

The solver computes and populates the data in the `location`

and
`state`

structure arrays and passes this data to your function. You can
define your function so that its output depends on this data. You can use any names instead of
`location`

and `state`

, but the function must have exactly
two arguments (or one argument if the function specifies the initial temperature).

`location`

— A structure containing these fields:`location.x`

— The*x*-coordinate of the point or points`location.y`

— The*y*-coordinate of the point or points`location.z`

— For a 3-D or an axisymmetric geometry, the*z*-coordinate of the point or points`location.r`

— For an axisymmetric geometry, the*r*-coordinate of the point or points

Furthermore, for boundary conditions, the solver passes these data in the

`location`

structure:`location.nx`

—*x*-component of the normal vector at the evaluation point or points`location.ny`

—*y*-component of the normal vector at the evaluation point or points`location.nz`

— For a 3-D or an axisymmetric geometry,*z*-component of the normal vector at the evaluation point or points`location.nr`

— For an axisymmetric geometry,*r*-component of the normal vector at the evaluation point or points

`state`

— A structure containing these fields for transient or nonlinear problems:`state.u`

— Temperatures at the corresponding points of the location structure`state.ux`

— Estimates of the*x*-component of temperature gradients at the corresponding points of the location structure`state.uy`

— Estimates of the*y*-component of temperature gradients at the corresponding points of the location structure`state.uz`

— For a 3-D or an axisymmetric geometry, estimates of the*z*-component of temperature gradients at the corresponding points of the location structure`state.ur`

— For an axisymmetric geometry, estimates of the*r*-component of temperature gradients at the corresponding points of the location structure`state.time`

— Time at evaluation points

Thermal material properties (thermal conductivity, mass density, and specific heat) and internal heat source get these data from the solver:

`location.x`

,`location.y`

,`location.z`

,`location.r`

Subdomain ID

`state.u`

,`state.ux`

,`state.uy`

,`state.uz`

,`state.r`

,`state.time`

Boundary conditions (temperature on the boundary, heat flux, convection coefficient, and radiation emissivity coefficient) get these data from the solver:

`location.x`

,`location.y`

,`location.z`

,`location.r`

`location.nx`

,`location.ny`

,`location.nz`

,`location.nr`

`state.u`

,`state.time`

Initial temperature gets the following data from the solver:

`location.x`

,`location.y`

,`location.z`

,`location.r`

Subdomain ID

For all thermal parameters, except for thermal conductivity, your function must return a row
vector `thermalVal`

with the number of columns
equal to the number of evaluation points, for example, ```
M =
length(location.y)
```

.

For thermal conductivity, your function must return a matrix
`thermalVal`

with number of rows equal to 1, `Ndim`

,
`Ndim*(Ndim+1)/2`

, or `Ndim*Ndim`

, where
`Ndim`

is 2 for 2-D problems and 3 for 3-D problems. The number of columns
must equal the number of evaluation points, for example, ```
M =
length(location.y)
```

. For details about dimensions of the matrix, see c Coefficient for specifyCoefficients.

If properties depend on the time or temperature, ensure that your function returns a matrix of
`NaN`

of the correct size when `state.u`

or
`state.time`

are `NaN`

. Solvers check whether a problem is
time dependent by passing `NaN`

state values and looking for returned
`NaN`

values.

### Additional Arguments in Functions for Nonconstant Thermal Parameters

To use additional arguments in your function, wrap your function (that takes additional arguments) with an anonymous function that takes only the `location`

and `state`

arguments. For example:

thermalVal = ... @(location,state) myfunWithAdditionalArgs(location,state,arg1,arg2...) thermalBC(model,"Edge",3,"Temperature",thermalVal) thermalVal = @(location) myfunWithAdditionalArgs(location,arg1,arg2...) thermalIC(model,thermalVal)

## Version History

**Introduced in R2017a**

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