# Quiver Plots in MATLAB®

How to make Quiver Plots plots in MATLAB® with Plotly.

## Create Quiver Plot

Load sample data that represents air currents over North America. For this example, select a subset of the data.

X = x(11:22,11:22,1);
Y = y(11:22,11:22,1);
U = u(11:22,11:22,1);
V = v(11:22,11:22,1);

Create a quiver plot of the subset you selected. The vectors X and Y represent the location of the base of each arrow, and U and V represent the directional components of each arrow. By default, the quiver function shortens the arrows so they do not overlap. Call axis equal to use equal data unit lengths along each axis. This makes the arrows point in the correct direction.

X = x(11:22,11:22,1);
Y = y(11:22,11:22,1);
U = u(11:22,11:22,1);
V = v(11:22,11:22,1);

quiver(X,Y,U,V)
axis equal

fig2plotly(gcf);

## Disable Automatic Scaling

By default, the quiver function shortens arrows so they do not overlap. Disable automatic scaling so that arrow lengths are determined entirely by U and V by setting the scale argument to 0.

For instance, create a grid of X and Y values using the meshgrid function. Specify the directional components using these values. Then, create a quiver plot with no automatic scaling.

[X,Y] = meshgrid(0:6,0:6);
U = 0.25*X;
V = 0.5*Y;
quiver(X,Y,U,V,0)

fig2plotly(gcf);

## Plot Gradient and Contours

Plot the gradient and contours of the function z=xe-x2-y2. Use the quiver function to plot the gradient and the contour function to plot the contours.

First, create a grid of x- and y-values that are equally spaced. Use them to calculate z. Then, find the gradient of z by specifying the spacing between points.

spacing = 0.2;
[X,Y] = meshgrid(-2:spacing:2);
Z = X.*exp(-X.^2 - Y.^2);

Display the gradient vectors as a quiver plot. Then, display contour lines in the same axes. Adjust the display so that the gradient vectors appear perpendicular to the contour lines by calling axis equal.

spacing = 0.2;
[X,Y] = meshgrid(-2:spacing:2);
Z = X.*exp(-X.^2 - Y.^2);

quiver(X,Y,DX,DY)
hold on
contour(X,Y,Z)
axis equal
hold off

fig2plotly(gcf);

## Specify Arrow Color

Create a quiver plot and specify a color for the arrows.

[X,Y] = meshgrid(-pi:pi/8:pi,-pi:pi/8:pi);
U = sin(Y);
V = cos(X);
quiver(X,Y,U,V,'r')

fig2plotly(gcf);

## Specify Axes for Quiver Plot

Create a grid of X and Y values and two sets of U and V directional components.

[X,Y] = meshgrid(0:pi/8:pi,-pi:pi/8:pi);
U1 = sin(X);
V1 = cos(Y);
U2 = sin(Y);
V2 = cos(X);

Create a tiled layout of plots with two axes, ax1 and ax2. Add a quiver plot and title to each axes. (Before R2019b, use subplot instead of tiledlayout and nexttile.)

[X,Y] = meshgrid(0:pi/8:pi,-pi:pi/8:pi);
U1 = sin(X);
V1 = cos(Y);
U2 = sin(Y);
V2 = cos(X);

tiledlayout(1,2)

ax1 = nexttile;
quiver(ax1,X,Y,U1,V1)
axis equal
title(ax1,'Left Plot')

ax2 = nexttile;
quiver(ax2,X,Y,U2,V2)
axis equal
title(ax2,'Right Plot')

fig2plotly(gcf);

## Modify Quiver Plot After Creation

Create a quiver plot and return the quiver object. Then, remove the arrowheads and add dot markers at the base of each arrow.

[X,Y] = meshgrid(-pi:pi/8:pi,-pi:pi/8:pi);
U = sin(Y);
V = cos(X);

q = quiver(X,Y,U,V);