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# Documentation

## Syntax

```[ux,uy] = pdegrad(p,t,u)
```

## Description

[ux,uy] = pdegrad(p,t,u) returns the gradient of u evaluated at the center of each triangle.

Row i from 1 to N of ux contains

$\frac{\partial {u}_{i}}{\partial x}$

Row i from 1 to N of uy contains

$\frac{\partial {u}_{i}}{\partial y}$

There is one column for each triangle in t in both ux and uy.

The geometry of the PDE problem is given by the mesh data p and t. For details on the mesh data representation, see initmesh.

For a description of the format for the solution vector u, see assempde.

The optional argument sdl restricts the computation to the subdomains in the list sdl.