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# PDE Coefficients

Specify coefficients

Use the `specifyCoefficients` function to write the m, d, c, a, and f coefficients for equations of the form

`$m\frac{{\partial }^{2}u}{\partial {t}^{2}}+d\frac{\partial u}{\partial t}-\nabla ·\left(c\nabla u\right)+au=f$`

and eigenvalue equations of the form

`$\begin{array}{l}-\nabla ·\left(c\nabla u\right)+au=\lambda du\\ \text{or}\\ -\nabla ·\left(c\nabla u\right)+au={\lambda }^{2}mu\end{array}$`

You also can specify coefficients for a system of PDEs or an eigenvalue system. A PDE model stores coefficients as a vector of `CoefficientAssignment` objects in its `EquationCoefficients` property. After you specify PDE coefficients, you can adjust or delete them anytime before solving the PDE. For details, see View, Edit, and Delete PDE Coefficients.

Include a geometry in a PDE model before using `specifyCoefficients`.

## Functions

 `findCoefficients` Locate active PDE coefficients `specifyCoefficients` Specify coefficients in a PDE model

## Properties

 CoefficientAssignment Properties Coefficient assignments

## Topics

### Programmatic Workflow

f Coefficient for specifyCoefficients

Specify the coefficient f in the equation.

c Coefficient for specifyCoefficients

Specify the coefficient c in the equation.

m, d, or a Coefficient for specifyCoefficients

Specify the coefficients m, d, a in the system of equations or in the eigenvalue system.

View, Edit, and Delete PDE Coefficients

Access and modify coefficient assignments stored in the EquationCoefficients property of PDEModel by using the findCoefficients function.

### PDE Modeler App Workflow

Coefficients for Scalar PDEs in PDE Modeler App

Interactively specify coefficients for 2-D problems.

Coefficients for Systems of PDEs in the PDE Modeler App

Interactively specify coefficients for systems of two 2-D PDEs.

Coefficients That Depend on Time and Space in the PDE Modeler App

Interactively specify coefficients for 2-D problems.

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