<< Chapter < Page Chapter >> Page >
Basic curve fitting and linear regression.


What is regression analysis?

Suppose we calculate some variable of interest, y, as a function of some other variable x. We call y the dependent variable and x the independent variable. For example, consider the data set below, taken from a simple experiment involving a vehicle, its velocity versus time is tabulated. In this case, velocity is a function of time, thus velocity is the dependent variable and the time is the independent variable.

Vehicle velocity versus time.
Time [s] Velocity [m/s]
0 20
10 39
20 67
30 89
40 111
50 134
60 164
70 180
80 200

In its simplest form regression analysis involves fitting the best straight line relationship to explain how the variation in a dependent variable, y, depends on the variation in an independent variable, x. In our example above, once the relationship (in this case a linear relationship) has been estimated we can produce a linear equation in the following form:

y m x n

And once an analytic equation such as the one above has been determined, dependent variables at intermediate independent values can be computed.

Performing linear regression

Regression analysis with MATLAB is easy. The MATLAB Basic Fitting GUI allows us to interactively to do "curve fitting" which is a method to arrive at the best "straight line" fit for linear equations or the best curve fit for a polynomial up to the tenth degree. The procedure to perform a curve fitting with MATLAB is as follows:

  1. Input the variables,
  2. Plot the data,
  3. Initialize the Basic Fitting GUI,
  4. Select the desired regression analysis parameters.

Using the data set above, determine the relationship between velocity and time.

First, let us input the variables (Workspace>New variable) as shown in the following figures.

A new variable is created in the Workspace.

New variables are entered in the Variable Editor.

Second, we will plot the data by typing in plot(time,velocity) at the MATLAB prompt. The following plot is generated, select Tools>Basic Fitting:

A plot is generated in Figure 1. The Basic Fitting tool can be initialized from Tools>Basic Fitting.

In the "Basic Fitting" window, select "linear" and "Show equations". The best fitting linear line along with the corresponding equation are displayed on the plot:

Basic Fitting window is used to select the desired regression analysis parameters.

Now let us do another curve fitting and obtain an equation for the function. Using that equation, we can evaluate the function at a desired value with polyval .

The following is a collection of data for an iron-constantan thermocouple (data available for download ). Engineering Fundamentals and Problem Solving by Arvid R. Eide, Roland Jenison, Larry L. Northup, Steven K. Mikelson , McGraw-Hill Higher Education. © 2007 p.114

Temperature [C] vs Voltage [mV]
Temperature [C] Voltage [mV]
50 2.6
100 6.7
150 8.8
200 11.2
300 17.0
400 22.5
500 26
600 32.5
700 37.7
800 41
900 48
1000 55.2
  1. Plot a graph with Temperature as the independent variable.
  2. Determine the equation of the relationship using the Basic Fitting tools.
  3. Estimate the Voltage that corresponds to a Temperature of 650 C and 1150 C.

We will input the variables first:

Temp=[50;100;150;200;300;400;500;600;700;800;900;1000] Voltage=[2.6;6.7;8.8;11.2;17;22.5;26;32.5;37.7;41;48;55.2]

To plot the graph, type in:


We can now use the Plot Tools and Basic Fitting settings and determine the equation:

Basic Fitting window is used to select the desired regression analysis parameters.

By clicking the right arrow twice at the bottom right corner on the Basic Fitting window, we can evaluate the function at a desired value. See the figure below which illustrates this process for the temperature value 1150 C.

Estimating the Voltage that corresponds to a Temperature of 1150 C.

Now let us check our answer with a technique we learned earlier. As displayed on the plot, we have obtained the following equation: y 0.052831 x 0.67202 This equation can be entered as polynomial and evaluated at 650 and 1150 as follows:

>>p=[0.052831,0.67202] p =0.0528 0.6720>>polyval(p,1150) ans =61.4277

Summary of key points

  1. Linear regression involves fitting the best straight line relationship to explain how the variation in a dependent variable, y, depends on the variation in an independent variable, x,
  2. Basic Fitting GUI allows us to interactively perform curve fitting,
  3. Some of the plot fits available are linear, quadratic and cubic functions,
  4. Basic Fitting GUI can evaluate functions at given points.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, A brief introduction to engineering computation with matlab. OpenStax CNX. Nov 17, 2015 Download for free at http://legacy.cnx.org/content/col11371/1.11
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'A brief introduction to engineering computation with matlab' conversation and receive update notifications?