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PHYS210 2009-10-27 LAB SUMMARY

1) The ~/.octaverc file (octave start-up file)
2) Octave "core files"
3) Simple 2D plotting with octave
4) Lab assignment (see handout)

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1) The ~/.octaverc file (octave start-up file)
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Commands in the hidden file ~/.octaverc are executed every time 
octave starts.  This is a convenient place to add components to 
octave's path, i.e. to the list of directories in which it will 
search for function and script .m files

Change to your home directory, and using your text editor create 
the file .octaverc so that it contains the lines between the 
-------'s below

% cd 
% [kate, gedit, xemacs, vi, ...] .octaverc

------------------------------------------------------------------------
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Start-up file for octave
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Add path components
addpath('~/octave');
addpath('/home/phys210/octave');
addpath('/home/phys210/octave/hw3');
------------------------------------------------------------------------

Now, start octave  (>> stands for the octave prompt)

% octave

and type greetings

>> greetings

A message such as the following should appear

Greetings, user phys210t!

'greetings' is a octave function defined in the ~phys210/octave, and
you can see its definition (as well as verifying the location of 
the source file) using the 'type' command (this works for all 
MATLAB / octave function, although no octave code is displayed for 
built-in functions)

>> type greetings

greetings is the user-defined function defined from: /home/phys210/octave/greetings.m

function [] = greetings()
   fprintf('Greetings, user %s!\n',getenv('LOGNAME'));
end

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2) Octave "core files"
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From time to time octave may terminate abnormally, particularly if 
you use Ctrl-C to interrupt a calculation that is taking an
inordinately long time.

In such instances, octave may 'dump core'---i.e. write a memory 
image to a file that, in principle, can later be loaded into 
octave to resume the computation.  In most cases, however, you 
will not want to use this resume feature, and the file that is 
produced (which always has the name octave-core) can be quite 
large.  Thus, if you notice an 'octave-core' file while working 
with octave, it is best to remove it.

Also, there is an octave function, octave_core_file_limit,
which can be used to control the size of the core file.  Recommended
practice, then (unless you really think you can make use of the 
restore feature), is to put the following line in your 
~/.octaverc

octave_core_file_limit(1.0e-10);

which will limit the size of octave-core to a few bytes.
Note that octave_core_file_limit(0) doesn't do what you 
might expect, and in fact generates an error message.

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3) Simple 2D plotting with octave
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Ensure that you are in your ~/octave directory, start up 
octave and execute 'plotex'

% cd ~/octave
% octave
>> plotex

You should see output such as the following on your terminal, 
and, as the script executes, you should also see various plots
appearing in a separate plotting window labelled 'Figure 1'.
If this doesn't work for you, ask for help.

   The following is a plot of

      sin(x)*sin(3x) for 0 <= x <= 2 pi, and using

      - 1000 points uniformly distributed in the interval
      - default plotting style (line)
      - default line color
      - default annotations (no title, axes labels or legend)

   Type 'Enter' to continue:
   The following is a plot of

      sin(x)*sin(3x) for 0 <= x <= 2 pi, using

      - 1000 points uniformly distributed in the interval
      - points plotting style, with small green circles for the points
      - a title and axes labels

   Type 'Enter' to continue:
   The following is a plot of

      sin(x)*sin(3x) AND cos(5x)*cos(2x) for 0 <= x <= 2 pi, using

      - 1000 points uniformly distributed in the interval
      - red +'s for the first data set, a cyan line for the second
      - a title, axes labels and legend
   Also, a hardcopy of the figure is saved as 'plot.ps'

   You should see 'plot.ps' in the following listing of the current directory

   hello.m  probs1.m  probs2.m  Probs3.m     threeoutargs.m  t_threeoutargs.m
   plot.ps  Probs1.m  Probs2.m  sintaylor.m  t_sintaylor.m

Once you have finished with this demo, study the script file 
/phys210/octave/plotex.m
to see how the plots were generated. 

You can use this file as a template to work from for today's 
assignments, as well as current and upcoming homework, your 
term projects etc.

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4) Lab assignment (see handout)
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