## Documentation Center |

You can enter coefficients for a system with *N* = `2` equations
in the PDE app, see Systems of PDEs.
To do so, open the PDE app and select `Generic System`.

Then select **PDE > PDE Specification**.

Enter string expressions for coefficients using the form in Coefficients for Scalar PDEs in PDE App, with additional options for nonlinear equations. The additional options are:

Represent the

`i`th component of the solution`u`using`'u(i)'`for`i`= 1 or 2.Similarly, represent the

`i`th components of the gradients of the solution`u`using`'ux(i)'`and`'uy(i)'`for`i`= 1 or 2.

Do not use quotes or unnecessary spaces in your entries.

For higher-dimensional systems, do not use the PDE app. Represent your problem coefficients at the command line.

You can enter scalars into the `c` matrix,
corresponding to these equations:

If you need matrix versions of any of the `cij` coefficients,
enter expressions separated by spaces. You can give 1-, 2-, 3-, or
4-element matrix expressions. These mean:

1-element expression:

2-element expression:

3-element expression:

4-element expression:

For details, see c for Systems.

For example, these expressions show one of each type (1-, 2-, 3-, and 4-element expressions)

These expressions correspond to the equations

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