# tri2grid

(Not recommended) Interpolate from PDE triangular mesh to rectangular grid

`tri2grid` is not recommended. Use `interpolateSolution` instead.

## Syntax

```uxy = tri2grid(p,t,u,x,y) [uxy,tn,a2,a3] = tri2grid(p,t,u,x,y) uxy = tri2grid(p,t,u,tn,a2,a3) ```

## Description

`uxy = tri2grid(p,t,u,x,y)` computes the function values `uxy` over the grid defined by the vectors `x` and `y`, from the function `u` with values on the triangular mesh defined by `p` and `t`. Values are computed using linear interpolation in the triangle containing the grid point. The vectors `x` and `y` must be increasing. `u` must be a vector. For systems of equations, `uxy` interpolates only the first component. For solutions returned by `hyperbolic` or `parabolic`, pass `u` as the vector of values at one time, `u(:,k)`.

`[uxy,tn,a2,a3] = tri2grid(p,t,u,x,y)` additionally lists the index `tn` of the triangle containing each grid point, and interpolation coefficients `a2` and `a3`.

`uxy = tri2grid(p,t,u,tn,a2,a3)` with `tn`, `a2`, and `a3` computed in an earlier call to `tri2grid`, interpolates using the same grid as in the earlier call. This variant is, however, much faster if several functions have to be interpolated using the same grid, such as interpolating hyperbolic or parabolic solutions at multiple times.

All `tri2grid` output arguments are `ny`-by-`nx` matrices, where `nx` and `ny` are the lengths of the vectors `x` and `y` respectively. At grid points outside of the triangular mesh, all `tri2grid` output arguments are `NaN`. 