Plotting With Matlab

Plotting with Matlab

• x = 0:pi/30:2*pi;

• % x vector, 0 <= x <= 2*pi, increments of pi/30

• y = sin(3*x); % vector of y values

• plot(x,y) % create the plot

• xlabel('x (radians)'); % label the x-axis ylabel('sine function'); % label the y-axis > title('sin(3*x)'); % put a title on the plot

Symbol plot• plot(x,y,'o');

• plot(x,y,'r:');

Symbol plot

• x = 0:0.01:2; % generate the x-vector noise = 0.02*randn(size(x)); % and noise

• y = 5*x.*exp(-3*x) + noise; % Add noise to known function

• plot(x,y,'o'); % and plot with symbols • xlabel('x (arbitrary units)'); % add axis

labels and plot title • ylabel('y (arbitrary units)'); • title('Plot of y = 5*x*exp(-3*x) + noise');

Multiple plots

• The legend is used to label the different data curves when more than one curve is drawn on the same plot. The syntax is legend('label1','label2',...)

• The plot command will put multiple curves on the same plot with the following syntax plot(x1,y1,s1,x2,y2,s2,x3,y3,s3,...)

Plot from file

• load PDXprecip.dat; % read data into PDXprecip matrix • month = PDXprecip(:,1); % copy first column of

PDXprecip into month• precip = PDXprecip(:,2); % and second column into

precip • plot(month,precip,'o'); % plot precip vs. month with

circles • xlabel('month of the year'); % add axis labels and plot

title • ylabel('mean precipitation (inches)'); • title('Mean monthly precipitation at Portland International

Airport');

Multiple plots in the same window

• Hold on

• By default, MATLAB finds the maxima and minima of the data and chooses the axis limits to span this range.

• The axis command enables you to specify your own limits:

• axis([xmin xmax ymin ymax])

• Grid -Setting Grid Lines

Adding text

• text(1,-1/3,'{\itNote the odd symmetry.}')

• Disp(‘text’)

Programmatic Plotting • Prepare your data• Select a window and position a plot region within

the window• Call elementary plotting function• Select line and marker characteristicsset(h,'LineWidth',2,{'LineStyle'}, {'--';':';'-.'})set(h,{'Color'},{'r';'g';'b'})• Set axis limits, tick marks, and grid lines• Annotate the graph with axis labels, legend, and

text• Export graph

• t = 0:pi/100:2*pi;

• y = sin(t);

• plot(t,y)

• grid on % Turn on grid lines for this plot

• y = sin(t);

• y2 = sin(t-0.25);

• y3 = sin(t-0.5);

• plot(t,y,t,y2,t,y3)

Different linestyles

• t = 0:pi/100:2*pi;

• y = sin(t);

• y2 = sin(t-0.25);

• y3 = sin(t-0.5);

• plot(t,y,'-',t,y2,'--',t,y3,':')

Colors, Line Styles, and Markers • The basic plotting functions accepts character-string arguments that

specify various line styles, marker symbols, and colors for each vector plotted.

• In the general form,plot(x,y,'linestyle_marker_color') linestyle_marker_color is a character string (delineated by single

quotation marks) constructed from• A line style (e.g., dashed, dotted, etc.)• A marker type (e.g., x, *, o, etc.)• A predefined color specifier (c, m, y, k, r, g, b, w)

plot(x,y,':squarey') plots a yellow dotted line and places square markers at each data point. If you specify a marker type, but not a line style, only the marker is plotted.

• The specification can consist of one or none of each specifier in any order.

• For example, the string 'go--' defines a dashed line with circular markers, both colored green

Graphics handlers

• x = 1:10; y = x.^3; h = plot(x,y);

• You can use the handle h to set the properties of the lineseries object. For example, you can set its Color property

• set(h,'Color','red')

• get(h,'LineWidth')

Graphical user interface

• guide

Supported Image Formats

• MATLAB supports the following graphics file formats, along with others:

• BMP (Microsoft Windows Bitmap)• GIF (Graphics Interchange Files)• HDF (Hierarchical Data Format)• JPEG (Joint Photographic Experts Group)• PCX (Paintbrush)• PNG (Portable Network Graphics)• TIFF (Tagged Image File Format)• XWD (X Window Dump)

• MATLAB math supports three different numeric classes for image display:

• double-precision floating-point (double)

• 16-bit unsigned integer (uint16)

• 8-bit unsigned integer (uint8)

Image functions and utlities

• Image image (create image object).• imagescScale data and display as image.• imreadRead image from graphics file.File I/O• imwriteWrite image to graphics file.File I/O• imfinfoGet image information from graphics

file.Utility• ind2rgbConvert indexed image to RGB

image.Utility

Image Types

• Indexed Images

• Intensity Images

• RGB (Truecolor) Images

Image loading• Load or save a matrix as a MAT-file.• load• Save• Load or save graphics file format image, e.g., BMP, TIFF.• Imread• Imwrite• Display any image loaded into the MATLAB workspace.• Image• Imagesc• Utilities • imfinfo • ind2rgb

• load mandrill

• figure('color','k')

• image(X)

• colormap(map)

• axis off % Remove axis ticks and numbers axis image % Set aspect ratio to obtain square pixels

• Figure• ax(1) = subplot(1,2,1); • rgb = imread('ngc6543a.jpg'); • image(rgb); • title('RGB image')• ax(2) = subplot(122); • im = mean(rgb,3); • image(im); • title('Intensity Heat Map') • colormap(hot(256))• linkaxes(ax,'xy') • axis(ax,'image')

Coloring Techniques

• You can enhance the information content of surface plots by controlling the way MATLAB graphics apply color to these plots. MATLAB can map particular data values to colors specified explicitly or can map the entire range of data to a predefined range of colors called a colormap.

three different coloring techniques

• Indexed Color Surfaces — Direct and Scaled Color Mapping —• MATLAB colors the surface plot by assigning each data point an

index into the figure's colormap. The way MATLAB applies these colors depends on the type of shading used (faceted, flat, or interpolated).

• Truecolor Surfaces — MATLAB colors the surface plot using the explicitly specified colors (i.e., the RGB triplets). The way MATLAB applies these colors depends on the type of shading used (faceted, flat, or interpolated). To be rendered accurately, truecolor requires computers with 24-bit displays; however, MATLAB simulates truecolor on indexed systems. See the shading command for information on the types of shading.(OpenGL method)

• Texture Mapping — Texture mapping displays a 2-D image mapped onto a 3-D surface.

Color maps

• Each MATLAB figure window has a colormap associated with it. A colormap is simply a three-column matrix whose length is equal to the number of colors it defines. Each row of the matrix defines a particular color by specifying three values in the range zero to one. These values define the RGB components (i.e., the intensities of the red, green, and blue video components).

• The colormap function, with no arguments, returns the current figure's colormap. For example, the MATLAB default colormap contains 64 colors and the 57th color is red.

• cm = colormap;

• cm(57,:)

• ans = 1 0 0

RGB Color Components Red Green Blue Color

0 0 0 Black1 1 1 White1 0 0 Red0 1 0 Green0 0 1 Blue1 1 0 Yellow1 0 1 Magenta0 1 1 Cyan0.5 0.5 0.5 Gray0.5 0 0 Dark red1 0.62 0.40 Copper0.49 1 0.83 Aquamarine

• You can create colormaps with MATLAB array operations or you can use any of several functions that generate useful maps, including hsv, hot, cool, summer, and gray.

• Each function has an optional parameter that specifies the number of rows in the resulting map.

Displaying Colormaps

• The colorbar function displays the current colormap, either vertically or horizontally, in the figure window along with your graph. For example, the statements

• [x,y] = meshgrid([-2:.2:2]);• Z = x.*exp(-x.^2-y.^2);• surf(x,y,Z,gradient(Z)) • colorbar • produce a surface plot and a vertical strip of color

corresponding to the colormap. The colorbar indicates the mapping of data value to color with the axis labels.

Total graphicsPrepare your data.• Z = peaks(20);Select window and position plot region within window.• figure(1);subplot(2,1,2)Call 3-D graphing function.• h = surf(Z);Set colormap and shading algorithm.• colormap hot shading interp set(h,'EdgeColor','k')Add lighting.light('Position',[-2,2,20]) lighting phong material([0.4,0.6,0.5,30])

set(h,'FaceColor',[0.7 0.7 0],... 'BackFaceLighting','lit') Set viewpoint • view([30,25])• set(gca,'CameraViewAngleMode','Manual')

Set axis limits and tick marks.• axis([5 15 5 15 -8 8]) set(gca,'ZTickLabel','Negative||

Positive')Set aspect ratio.• set(gca,'PlotBoxAspectRatio',[2.5 2.5 1])Annotate the graph with axis labels, legend, and text.• xlabel('X Axis') ylabel('Y Axis') zlabel('Function

Value') title('Peaks')Print graph.• set(gcf,'PaperPositionMode','auto') print -dps2

3D plot

• t = 0:pi/50:10*pi;

• plot3(sin(t),cos(t),t)

• axis square; grid on

Plotting matrix data

• [X,Y] = meshgrid([-2:0.1:2]);

• Z = X.*exp(-X.^2-Y.^2);

• plot3(X,Y,Z)

• grid on

Visualizing Functions of Two Variables

• To display a function of two variables, z = f(x,y), generate X and Y matrices consisting of repeated rows and columns, respectively, over the domain of the function. You will use these matrices to evaluate and graph the function.

• The meshgrid function transforms the domain specified by two vectors, x and y, into matrices X and Y. You then use these matrices to evaluate functions of two variables: The rows of X are copies of the vector x and the columns of Y are copies of the vector y.

The rest

• Lighting control

• Object transparency

• Visualizing volume functions