Scott: /* File I/O */

2013-01-31T22:49:53Z

File I/O

← Older revision		Revision as of 22:49, 31 January 2013
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	</source>		</source>
	may also use '''<code>csvread, csvwrite, dlmread, dlmwrite, textread, xlsread</code>'''		may also use '''<code>csvread, csvwrite, dlmread, dlmwrite, textread, xlsread</code>'''

			== Troubleshooting ==
			When starting matlab 2012a, I get this error at the command line:
			<pre>
			/nfs/pkg64/matlab_2012a/bin/matlab: 1: /nfs/pkg64/matlab_2012a/bin/util/oscheck.sh: /lib64/libc.so.6: not found
			</pre>
			Fix it like this:
			<pre>
			sudo ln -s /lib/x86_64-linux-gnu/libc-2.15.so /lib64/libc.so.6
			</pre>

Scott: /* Control Flow */

2011-01-31T23:22:55Z

Control Flow

New page

==Operators==
* 2\1 is equivalent to 1/2
<source lang="matlab">
psi = C .* 1./(1+(x./a).^2);
</source>
* The dot denotes pair-by-pair operation for vectors
* Technically, you only need dots in front of ^ operators for which the first argument might be a vector, and <nowiki>*</nowiki> and / operators for which the quantities on each side of the operator could ''both'' be vectors. The MATLAB function <code>quad</code> gives a vector argument to the function it is integrating, so vectors may crop up when you don't expect them. The safest thing is to put a dot in front of every <nowiki>*</nowiki>, /, and ^ operator in all your functions. Otherwise, you may get hard-to-understand error messages.

==Working at the command line==

* semicolon at end of line prevents result from being displayed
* '''<code>clear</code>''' clears all session variables, '''<code>clear x</code>''' clears the variable x
* '''<code>whos</code>''' shows all session variables
* '''<code>size(x)</code>''' shows the dimensions of x
* '''<code>clc</code>''' clears the command window
* use '''<code>diary mynotes.txt</code>''' to append command window input/output to the file mynotes.txt; use '''<code>diary off</code>''' to stop appending
* '''<code>disp(x)</code>''' will display the value of x
* '''<code>format</code>''' controls format of numeric output

==Built-in scalar functions==

* '''<code>fix</code>''' rounds to nearest integer toward zero, '''<code>floor</code>''', '''<code>ceil</code>'''
* '''<code>log, log10, pow2</code>''' (two to the x)
* '''<code>realmin, realmax</code>''' smallest and largest floating point numbers supported
* '''<code>rand</code>''' in the interval [0,1)
* '''<code>rem(x,y)</code>''' remainder when x is divided by y

==Vectors==

* create a sequence vector: '''<code><br /></code>'''

# <code>x = 1:5</code> (one through five, inclusive)
# x = 1: 0.1: 5 (one through five in steps of 0.1)

* create an arbitrary vector:

# x = [5 2 9 4 8]
# x = [5, 2, 9, 4, 8] (may use commas or spaces)
# y = [1 x 1] (has 7 elements)

* multiply: '''<code>y = 2*x</code>'''
* add: '''<code>x + y</code>'''
* get the first element: '''<code>x(1)</code>'''
* get the first three elements: '''<code>x(1:3)</code>'''
* column vector using transpose: '''<code>y = x'</code>'''
* append an element: '''<code>x = [ x 3 ]</code>'''
* remove an element '''<code>x(3) = []</code>'''
* built-in vector functions: '''<code>cumsum</code>''' (cumulative sum), '''<code>length</code>''', '''<code>max</code>''', '''<code>mean</code>''', '''<code>min</code>''', '''<code>prod</code>''', '''<code>sum</code>'''

==Matrices==
<source lang="matlab">
x = [1 2 3; 4 5 6]
x(1, 2) (gives 2)
x' % transpose
x(2, :) % gives [4 5 6]
a = [1 2; 3 4], b = a'
a * b % matrix multiplication give [5 11; 11 25]
a .* b % element-by-element multiplication gives [1 6; 6 16]
</source>

== Control Flow ==
<source lang="matlab">
for i = 1:5, disp(i), end
</source>

<source lang="matlab">
for i = 1:6
x = (x + a / x) / 2;
disp( x )
end
</source>

<source lang="matlab">
if x == 0, disp( ’x equals zero’), end
</source>

<source lang="matlab">
if bal < 5000
rate = 0.09;
elseif bal < 10000
rate = 0.12;
else
rate = 0.15;
end
</source>

<source lang="matlab">
d = floor(3*rand) + 1
switch d
case 1
disp( ’That’’s a 1!’ );
case 2
disp( ’That’’s a 2!’ );
otherwise
disp( ’Must be 3!’ );
end
</source>

== Functions ==
The existence of a file on disk called stat.m containing this code defines a new function called stat that calculates the mean and standard deviation of a vector:
<source lang="matlab">
function [mean,stdev] = stat(x)
n = length(x);
mean = sum(x)/n;
stdev = sqrt(sum((x-mean).^2/n));
</source>
Call the function, supplying two output variables on the left side of the equation:
<source lang="matlab">
[mean stdev] = stat([12.7 45.4 98.9 26.6 53/1])
mean =
47.3200
stdev =
29.4085
</source>

== Timing ==
<source lang="matlab">
start = clock;
.. do stuff ..
elapsed = etime(clock, start)
</source>
or equivalently
<source lang="matlab">
tic
..do stuff..
toc % prints out elapsed time
</source>

==Date and Time==
* '''<code>clock</code>''' gives time and date in a six-element vector
* '''<code>date</code>''' gives a string like 02-Feb-2011

==Plotting==
<source lang="matlab">
x = 1:0.1:5
plot(x, sin(x)), grid
ezplot('sin(x)')
</source>
Plot two functions simultaneously:
<source lang="matlab">
fplot(@(x) [sin(x),cos(x)],[0,2*pi,-2,2])
</source>

== Printing ==
To print some text:
<source lang="matlab">
disp( [’The answer is ’, num2str(x)] );
fprintf( ’Interest rate: %6.3f New balance: %8.2f\n’, rate, balance);
</source>

== File I/O ==
<source lang="matlab">
save mydata.txt myVar -ascii
myVar = load('mydata.txt')
</source>
also
<source lang="matlab">
save mydata x y z % saves to mydata.mat
load mydata
</source>
may also use '''<code>csvread, csvwrite, dlmread, dlmwrite, textread, xlsread</code>'''

Matlab - Revision history

Scott: /* File I/O */

Scott: /* Control Flow */