# Documentation

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# poicalc

Fast solver for Poisson's equation on rectangular grid

`poicalc` is not recommended. To solve Poisson's equations, use `solvepde`. For details, see Solve Problems Using PDEModel Objects.

## Syntax

```u = poicalc(f,h1,h2,n1,n2)
u = poicalc(f,h1,h2)
u = poicalc(f)
```

## Description

`u = poicalc(f,h1,h2,n1,n2)` calculates the solution of Poisson's equation for the interior points of an evenly spaced rectangular grid. The columns of `u` contain the solutions corresponding to the columns of the right-hand side `f`. `h1` and `h2` are the spacings in the first and second direction, and `n1` and `n2` are the number of points.

The number of rows in `f` must be `n1*n2`. If `n1` and `n2` are not given, the square root of the number of rows of `f` is assumed. If `h1` and `h2` are not given, they are assumed to be equal.

The ordering of the rows in `u` and `f` is the canonical ordering of interior points, as returned by `poiindex`.

The solution is obtained by sine transforms in the first direction and tridiagonal matrix solution in the second direction. `n1` should be 1 less than a power of 2 for best performance.

#### Introduced before R2006a

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