# quiver

Quiver or velocity plot

## Syntax

```quiver(x,y,u,v) quiver(u,v) quiver(...,scale) quiver(...,LineSpec) quiver(...,LineSpec,'filled') quiver(...,'PropertyName',PropertyValue,...) quiver(ax,...) h = quiver(...) ```

## Description

A quiver plot displays velocity vectors as arrows with components `(u,v)` at the points `(x,y)`.

For example, the first vector is defined by components `u(1)`,`v(1)` and is displayed at the point `x(1)`,`y(1)`.

`quiver(x,y,u,v)` plots vectors as arrows at the coordinates specified in each corresponding pair of elements in `x` and `y`. The matrices `x`, `y`, `u`, and `v` must all be the same size and contain corresponding position and velocity components. However, `x` and `y` can also be vectors, as explained in the next section. By default, the arrows are scaled to just not overlap, but you can scale them to be longer or shorter if you want.

`quiver(u,v)` draws vectors specified by `u` and `v` at equally spaced points in the x-y plane.

`quiver(...,scale)` automatically scales the arrows to fit within the grid and then stretches them by the factor `scale`. `scale` `=` `2` doubles their relative length, and `scale` `=` `0.5` halves the length. Use `scale = 0` to plot the velocity vectors without automatic scaling. You can also tune the length of arrows after they have been drawn by choosing the Plot Edit tool, selecting the quiver object, opening the Property Editor, and adjusting the Length slider.

`quiver(...,LineSpec)` specifies line style, marker symbol, and color using any valid `LineSpec`. `quiver` draws the markers at the origin of the vectors.

`quiver(...,LineSpec,'filled')` fills markers specified by `LineSpec`.

`quiver(...,'PropertyName',PropertyValue,...)` specifies property name and property value pairs for the quiver objects the function creates.

`quiver(ax,...)` plots into the axes `ax` instead of into the current axes (`gca`).

`h = quiver(...)` returns the `Quiver` object.

### Expanding x- and y-Coordinates

MATLAB® expands `x` and `y` if they are not matrices. This expansion is equivalent to calling `meshgrid` to generate matrices from vectors:

```[x,y] = `meshgrid`(x,y); quiver(x,y,u,v) ```

In this case, the following must be true:

`length(x)` `=` `n` and `length(y)` `=` `m`, where `[m,n]` `=` `size(u)` `=` `size(v)`.

The vector `x` corresponds to the columns of `u` and `v`, and vector `y` corresponds to the rows of `u` and `v`.

## Examples

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Use `quiver` to display an arrow at each data point in `x` and `y` such that the arrow direction and length represent the corresponding values in `u` and `v`.

```[x,y] = meshgrid(0:0.2:2,0:0.2:2); u = cos(x).*y; v = sin(x).*y; figure quiver(x,y,u,v)```

Plot the gradient of the function $z=x{e}^{-{x}^{2}-{y}^{2}}$.

```[X,Y] = meshgrid(-2:.2:2); Z = X.*exp(-X.^2 - Y.^2); [DX,DY] = gradient(Z,.2,.2); figure contour(X,Y,Z) hold on quiver(X,Y,DX,DY) hold off```