Introduction to 2D Plotting in MATLAB

MATLAB Logo

Introduction to 2D Plotting in MATLAB

MATLAB not only helps us for calculation but also helps us in data analysis and visualization by plotting graphs and waveforms. It provides us with a ‘big picture’ of our data. Here I’m going to discuss about the 2D plotting in MATLAB. If you haven’t yet started with MATLAB please goto our Matlab Tutorials.

Plotting

Using fplot()

fplot() : It is used to plot between the specified limits. The function must be of the form y=f(x), where x is a vector whose specifies the limits, and y is a vector with the same size as x.

SYNTAX :

  1. fplot(fun, limits) – A function fun is plotted in between the limits specified
  2. fplot(fun, limits, linespace) – allows plotting fun with line specification
  3. fplot(fun, limits, tol) -allows plotting with relative error tolerance ‘tol’.If not specified default tolerance will be 2e-3 ie .2%  accuracy.
  4. fplot(fun, limits, tol, linespace) – allows plotting with relative tolerance and line specification

eg :


fplot( 'x.^2' , [0,10])

Output:

Output of fplot function in Matlab

Output of fplot function in Matlab

Using plot()

In this case we need to specify the functions for x and y separately .Here we use a function plot () in MATLAB library

plot(): allows 2-D line plotting

SYNTAX:



  1. plot(y)-plots the columns of y versus the index of each value when y is a real number. For complex y it is equivalent to plot (real (y),img(y))
  2. plot(x1,y1,……..xN,yN) – plots y versus x
  3. plot(x1,y1,linespace…..xN,yN,linespace)-plots y versus x along with line specification

eg :

x= linspace(0,10*pi,5); # linspace is not line specification it is used to generate linearly spaced vectors
y=sin (x);
plot(x,y)

Ouput :

Output of plot function in Matlab

Output of plot function in Matlab

NOTE:

  • linspace is an inbuilt function which generates equally spaced vectors.
  1.  linspace(a, b) – generates 100 linearly spaced vectors
  2.  linspace(a,b,n) – generates n linearly spaced vectors including a,b
  • sin()-Trignometric sine function

# For plotting 2 functions at a time



Syntax :poly(x1,y1,x2,y2)

eg:

x=0:10;
y=x.^2;
z=2:12;
t=x.^2;
plot(x,y,z,t)

Output :

Output of plot function in Matlab - Plotting 2 Functions at a Time

Output of plot function in Matlab – Plotting 2 Functions at a Time

NOTE:

  • To change the characteristics of the plot we can use plottools function. A box will pop up showing your output, we can change change the characteristics there like color, plot type. We can also more data to the plot.

Shortcut method for quick editing:

This might be handy for the people who are always get bored dealing with the menu box in plottools. For quick and simple editing we don’t have to deal with plottools. We can have a third argument in the plot function.

Syntax: plot ( x, y,’color or line style or data points’)

eg : plot (x, y,’r*–‘)  # A red dotted plot is obtained.

  1. Available colors are red, blue, magenta, black, white, green, yellow, cyan
  2. Data points can be marked
  3. Linestyle can be changed.
  • Regular line- ‘ – ‘
  • Dotted lines- ‘ : ‘
  • Dashed line- ‘ – – ‘

NOTE: 

Colorspec is a method of specifying colors. There are 3 ways with which you can specify color

Color Specifications of plot funtion in Matlab

Color Specifications of plot funtion in Matlab

eg :

x=1:5;
y=1:5;
z=x+y;
plot(z,'r*--')

Output:

Plotting Function in Red Dashed Line - Matlab

Plotting Function in Red Dashed Line – Matlab

Some useful info:

  • axis equal function allows us to make the axes equal
  • line() function allows us to join the line after data points are plotted.

Eg:

x=1:5;
y=1: 5;
z=x+y;
plot(z,'r*--')
axis equal

Output:

Plotting Function in Red Dashed Line with equal Axis – Matlab

Plotting Function in Red Dashed Line with equal Axis – Matlab

 Histogram and Pie Chart

MATLAB also helps us to plot Histogram and Pie chart.

Histogram

            hist() function helps us to plot the histogram .

SYNTAX:

  1. n=hist(y) – Bins the elements in vector y into 10 equally spaced containers and returns the number of elements in each container as a row vector.
  2. n=hist(y,x)- Where x is a vector, returns the distribution of y along length (x) bins with centers specified by x.
  3. n=hist(y,nbins) – Here nbins is scalar and uses it as number of bins

eg :

x=rand(1000,1); #rand function generates nxn matrix ; rand(m,n) generates mxn square matrix
fix(x);         # used to round it off to 0
hist(x,5)       # returns the distribution of x in 5 length bin;

Output:

Histogram usng hist function in Matlab

Histogram usinghist function in Matlab

Piechart

             pie() function helps us to plot the pie chart of our data.

SYNTAX:

  1. pie(x)- draws a pie chart with the data in x.
  2. pie(x,explode)-Offsets a slice from the pie.explode is a vector or matrix of zeroes and non zeroes corresponding to x.

eg:

marks=[10,20,30,40,50]
pie(marks)

Output:

Pie Chart using pie function in Matlab

Pie Chart using pie function in Matlab

We can plot our data using scatter() function. In this data may be some points in a plane. So instead of using plot function we can directly use scatter function

SYNTAX:

  1. scatter(x,y)-draws the markers in default size and color
  2. scatter(x,y,s)-draws markers with specified sizewith single color.
  3. scatter(….,markertype)-use the marker type instead of  ‘0’.
  4. scatter(…, filled)- Fills the markers.

eg :

x=rand(50,1);
y=rand(50,1);  # make sure that x and y equal length vectors
scatter(x,y)

Output:

Plotting Data using scatter function in Matlab

Plotting Data using scatter function in Matlab

For plotting filled polygons we may use fill() function. The vertices are listed along with the color to be filled.
SYNTAX:

  1. fill(x,y,)-Creates filled polygons from the data specified by x and y with color c.
  2. fill(x1,y1,c1….xN,yN,cN)- specifies multiple 2-D filled areas
  3. fill(x,y,colorspec)-  fills 2-D polygons specified by X and Y with the color specified by colorspec explained in earlier section

eg:

x=[1.0,4.0,2.5];
y=[1.0,1.0,4.0];
fill(x,y,'c')

Output:

Plotting Filled Polygons using fill function in Matlab

Plotting Filled Polygons using fill function in Matlab

LABELLING

MATLAB also allows labelling of axes.

  • xlabel() function allows to label the x axis.

SYNTAX: xlabel(‘string’)

  • ylabel() function allows labelling of y axis

SYNTAX: ylabel(‘string’)

  • title()– function allows giving title to our plot

SYNTAX: title(‘string’)

eg:

x=1 : 5;
y=x+1;
plot(x,y)
xlabel('X axis ')
ylabel(' Y axis ')
title('Y=X+1 PLOT')

Output :

Labelling of a plot

Labelling of a plot

Share this post