Matlab Area for the local group

What is MATLAB?

MATLAB is an interactive, matrix-based system for scientific and engineering calculations. You can solve complex numerical problems without actually writing a program. The name MATLAB is an abbreviation for MATrix LABoratory.

Where can I get MATLAB help?

MATLAB is among the most convenient ways to do linear algebra, time series analysis, and data analysis in general. No matter you want to do, MATLAB is probably your best bet (by the way I'm not paid or sponsored by MATLAB).

There are a number of ways you get an answer to your MATLAB question;
  • If you know the exact command you are seeking help about, type help command
  • If you are not sure what the command you are looking for is, but know a keyword about it, type lookfor keyword
  • Q: How do I find out about plotting a y vs. x figure? A: help plot
  • Q: How do I find out about making a contour plot? A: help contour
  • Q: How do I find out about doing some statistics? A: help stats
  • Q: How do I find out about plotting coastlines and continents? A: help map
  • Q: How do I find out about ??? ? A:help ??? or lookfor ???
  • The MATLAB's demo feature, which leads you through some of MATLAB's features
  • The MATLAB manuals in the unix room
  • ask me!
    • Online help:
  • Matlab documetation from MathWorks, the company that makes MATLAB
  • The Mapping Toolbox documentation from Mathworks
  • The Statistics Toolbox documentation from Mathworks
  • A MATLAB manual at the Department of Mathematics, University of Utah
  • A US Navy MATLAB tutorial
  • Post a message on or monitor the matlab newsgroup: comp.soft-sys.matlab

    • A brief list of the most basic MATLAB commands

    Some Basic Commands (Note command syntax is case-sensitive!)

     matlab    loads the program matlab into your workspace.
     help      accesses the comprehensive help area
     quit      quits matlab, returning you to the operating system.
     who       lists all of the variables in your matlab workspace.
     whos      list the variables and describe their matrix size.
     clear     deletes all matrices from active workspace.
     clear x   deletes the matrix  x  from active workspace.
     ...       the ellipsis defining a line continuation is three
               successive periods.
     save      saves all the matrices defined in the current     
               session into the file, matlab.mat.
     load      loads contents of matlab.mat into current workspace.
     save filename  saves the contents of workspace into 
                    filename.mat
     save filename x y z
               saves the matrices x, y and z into the file titled
               filename.mat.
     load filename  loads the contents of filename into current
                    workspace; the file can be a binary (.mat) file
                    or an ASCII file.
     !         the ! preceding any unix command causes the unix
               command to be executed from matlab.

    Let's get going:

  • Download the tar file: matlabdir.tar to your /home directory (ie. I would want to see /home/rwardle/matlabdir.tar).
  • untar the file: tar -xvf matlabdir.tar
  • type cd matlab, and then ls -l, you should see: 
           bin            - Directory containing matlab utility scripts that, 
                        hopefully, will never need changing 

       data           - Directory containing conmap and netcdf files used
                        by the matlab scripts in the examples dir

       examples       - Directory containing example matlab scripts 

       startup.m      - The file startup.m specifies startup options. 
                        You can modify the default search path, predefine 
                        variables in your workspace etc.
  • cd bin
  • ls -l gives 
           rcmp.m   - Function script to read in a conmap file
  • cd ../examples
  • ls -l gives 
          conmapexample.m    - script that reads in a conmap file 
                           and contours the data

      datacdfexample.m   - script that loads in a netcdf NCEP data 
                           file and displays a field.
  • cd ../data
  • ls -l gives 
          T2M.33.DJF.cmp     - conmap file used by conmapexample.m
 
      ncep.cdf           - netcdf file with NCEP data used by datacdfexample.m
  • cd ..
  • matlab - invoke matlab with a graphical user interface (gui)
  • matlab -nojvm - invoke matlab at the command prompt (my preference)
  • You will now see the matlab prompt: >>

    MATLAB paths:

    For matlab to run a script, matlab must be able to see it.
    That means you either 1) have the matlab workspace in the script's directory or 2) have the script in a directory that is in your matlab path.
    The second option is the best as you end up with all of your scripts together, you don't lose them and you can catalogue them more easily.

    To set up your matlab paths, you need to add lines to your startup.m file:

    addpath /home/rwardle/matlab/examples
  etc.
    Here, we have added a dir to the matlab path so we can invoke the .m files that are located there from any directory, say where the data files are located.
    A users default matlab path is /home/username/matlab so this doesn't have to be set.

    Examples

    1. Loading conmap files

  • >> cd ~/matlab/data
  • >> conmapexample
  • The matlab script conmapexample.m (in dir ~/matlab/examples) loads and displays data contained in the conmap file T2M.33.DJF.cmp
    The conmapexample.m script calls rcmp.m (in dir ~/matlab/bin (which is in the default path)) which reads in the conmap file (headers and all) and returns the array and renames it (to t2m in this example). It then does a simple contour plot.
  • In theory you should never have to modify the rcmp.m script. You just need to call as is shown in conmapexample.m, ie. you need to specify it's name and dir path.

    • 2. Loading netcdf files

  • This is easy!! All you have to do to load in a netcdf file is type >> ncload filename or >>ncload('filename').
  • As an example of loading in data from a netcdf and then manipulating it to produce a plot see netcdfexample.m

    • 3. Defining functions, plotting, time-series analysis

  • Check out demo_time.m in dir (~/matlab/examples)

    • 4. Computing quantities as a function of space and time and plotting

  • Check out demo_insol.m in dir (~/matlab/examples)