# specifyCoefficients

Specify coefficients in a PDE model

## Syntax

## Description

Coefficients of a PDE

`solvepde`

solves PDEs of the form

$$m\frac{{\partial}^{2}u}{\partial {t}^{2}}+d\frac{\partial u}{\partial t}-\nabla \xb7\left(c\nabla u\right)+au=f$$

`solvepdeeig`

solves PDE eigenvalue problems of the form

$$\begin{array}{l}-\nabla \xb7\left(c\nabla u\right)+au=\lambda du\\ \text{or}\\ -\nabla \xb7\left(c\nabla u\right)+au={\lambda}^{2}mu\end{array}$$

`specifyCoefficients`

defines the coefficients
*m*, *d*, *c*, *a*,
and *f* in the PDE model.

`specifyCoefficients(`

defines the specified coefficients in each `model`

,`Name,Value`

)`Name`

to each
associated `Value`

, and includes them in `model`

.
You must specify all of these names: `m`

, `d`

,
`c`

, `a`

, and `f`

. This
syntax applies coefficients to the entire geometry.

**Note**

Include geometry in `model`

before using
`specifyCoefficients`

.

`specifyCoefficients(`

assigns coefficients for a specified geometry region.`model`

,`Name,Value`

,`RegionType`

,`RegionID`

)

## Examples

## Input Arguments

## Output Arguments

## More About

## Tips

For eigenvalue equations, the coefficients cannot depend on the solution

`u`

or its gradient.You can transform a partial differential equation into the required form by using Symbolic Math Toolbox™. The

`pdeCoefficients`

(Symbolic Math Toolbox) converts a PDE into the required form and extracts the coefficients into a structure that can be used by`specifyCoefficients`

.The

`pdeCoefficients`

function also can return a structure of symbolic expressions, in which case you need to use`pdeCoefficientsToDouble`

(Symbolic Math Toolbox) to convert these expressions to double format before passing them to`specifyCoefficients`

.

## Version History

**Introduced in R2016a**

## See Also

`findCoefficients`

| `PDEModel`

| `pdeCoefficients`

(Symbolic Math Toolbox) | `pdeCoefficientsToDouble`

(Symbolic Math Toolbox)