started working step by step through octave session

README.md

@@ -11,50 +11,5 @@ This repository is a placeholder for any and all attempts to replicate parts of
 
 In the first instance we'll attempt to recreate the ML/PGM Octave tutorials using the Enthought SciPy/Python distribution.  Here's the start of a transcript based on Prof Ng's [Octave transcript](http://spark-university.s3.amazonaws.com/stanford-pgm/slides/octave_session.m)
 
-In [2]: 5+6  
-Out[2]: 11
+[ipython transcript](ipython_transcript.txt)
 
-In [3]: 3-2    
-Out[3]: 1
-
-In [4]: 5*8  
-Out[4]: 40
-
-In [5]: 1/2  
-Out[5]: 0
-
-In [6]: 1/2.  
-Out[6]: 0.5
-
-In [7]: 2^6  
-Out[7]: 4
-
-In [8]: 2**6  
-Out[8]: 64
-
-In [9]: 1 == 2  
-Out[9]: False
-
-In [10]: 1 != 2  
-Out[10]: True
-
-In [14]: 1 and 0  
-Out[14]: 0
-
-In [15]: 1 or 0  
-Out[15]: 1
-
-In [18]: 1 ^ 0  
-Out[18]: 1
-
-In [19]: 1 ^ 1  
-Out[19]: 0
-
-In [20]: 
-
-In [20]: 0 ^ 0  
-Out[20]: 0
-
-In [21]: 
-
-More coming soon ...

ipython_session.py

@@ -0,0 +1,250 @@
+# Machine learning class (sort of ...)
+# iPython tutorial 
+
+# =======================================================
+# Section 1: iPython Tutorial: Basic operations
+
+# elementary operations
+
+5+6
+3-2
+5*8
+1/2. # note need for floating point specification - can fix via 'from __future__ import division'
+2**6 # raising to power is ^ in Octave
+1 == 2  # false
+1 != 2  # true.  note, not "~="
+1 & 0 # OR 1 and 0
+1 | 0 # OR 1 or 0
+1 ^ 0 # this is XOR in python
+
+
+## variable assignment
+a = 3; # semicolon optional - has no particular effect other than to allow multiple statements on a single line
+b = 'hi'
+c = 3>=1
+
+# Displaying them:
+a = pi
+print '2 decimals: %0.2f' % a # note use of % instead of , as in Octave
+print '6 decimals: %0.6f' % a 
+
+
+# Octave's global formatting not supported in Python - would have to import Decimal and even then things a bit sticky
+# format long
+# format short
+
+
+%%  vectors and matrices
+A = [1 2; 3 4; 5 6]
+
+v = [1 2 3]
+v = [1; 2; 3]
+v = [1:0.1:2]  % from 1 to 2, with stepsize of 0.1. Useful for plot axes
+v = 1:6        % from 1 to 6, assumes stepsize of 1
+
+C = 2*ones(2,3)  % same as C = [2 2 2; 2 2 2]
+w = ones(1,3)    % 1x3 vector of ones
+w = zeros(1,3)
+w = rand(1,3)  % drawn from a uniform distribution 
+w = randn(1,3) % drawn from a normal distribution (mean=0, var=1)
+w = -6 + sqrt(10)*(randn(1,10000))  % (mean = 1, var = 2)
+hist(w)
+I = eye(4)    % 4x4 identity matrix
+
+% help function
+help eye
+help rand
+
+% =======================================================
+% Section 2: Octave Tutorial: Moving data around 
+
+
+%% dimensions
+sz = size(A)
+size(A,1)  % number of rows
+size(A,2)  % number of cols
+length(v)  % size of longest dimension
+
+
+%% loading data
+pwd    % show current directory (current path)
+cd 'C:\Users\ang\Octave files'   % change directory 
+ls     % list files in current directory 
+load q1y.dat
+load q1x.dat
+who    % list variables in workspace
+whos   % list variables in workspace (detailed view) 
+clear q1y       % clear w/ no argt clears all
+v = q1x(1:10);
+save hello v;   % save variable v into file hello.mat
+save hello.txt v -ascii; % save as ascii
+% fopen, fread, fprintf, fscanf also work  [[not needed in class]]
+
+%% indexing
+A(3,2)  % indexing is (row,col)
+A(2,:)  % get the 2nd row. 
+        % ":" means every element along that dimension
+A(:,2)  % get the 2nd col
+A([1 3],:)
+
+A(:,2) = [10; 11; 12]     % change second column
+A = [A, [100; 101; 102]]; % append column vec
+A(:) % Select all elements as a column vector.
+
+% Putting data together 
+A = [A [100; 101; 102]]
+B = [11 12; 13 14; 15 16] % same dims as A
+[A B]
+[A; B] 
+
+
+% =======================================================
+% Section 3: Octave Tutorial: Computing on data 
+
+
+%% matrix operations
+A * C  % matrix multiplication
+A .* B % element-wise multiplcation
+% A .* C  or A * B gives error - wrong dimensions
+A .^ 2
+1./v
+log(v)  % functions like this operate element-wise on vecs or matrices 
+exp(v)  % e^4
+abs(v)
+
+-v  % -1*v
+
+v + ones(1,length(v))
+% v + 1  % same
+
+A'  % matrix transpose
+
+%% misc useful functions
+
+% max  (or min)
+a = [1 15 2 0.5]
+val = max(a)
+[val,ind] = max(a)
+
+% find
+a < 3
+find(a < 3)
+A = magic(3)
+[r,c] = find(A>=7)
+
+% sum, prod
+sum(a)
+prod(a)
+floor(a) % or ceil(a)
+max(rand(3),rand(3))
+max(A,[],1)
+min(A,[],2)
+A = magic(9)
+sum(A,1)
+sum(A,2)
+sum(sum( A .* eye(9) ))
+sum(sum( A .* flipud(eye(9)) ))
+
+
+% Matrix inverse (pseudo-inverse)
+pinv(A)        % inv(A'*A)*A'
+
+
+% =======================================================
+% Section 4: Octave Tutorial: Plotting 
+
+
+%% plotting
+t = [0:0.01:0.98];
+y1 = sin(2*pi*4*t); 
+plot(t,y1);
+y2 = cos(2*pi*4*t);
+hold on;  % "hold off" to turn off
+plot(t,y2,'r');
+xlabel('time');
+ylabel('value');
+legend('sin','cos');
+title('my plot');
+print -dpng 'myPlot.png'
+close;           % or,  "close all" to close all figs
+
+figure(2), clf;  % can specify the figure number
+subplot(1,2,1);  % Divide plot into 1x2 grid, access 1st element
+plot(t,y1);
+subplot(1,2,2);  % Divide plot into 1x2 grid, access 2nd element
+plot(t,y2);
+axis([0.5 1 -1 1]);  % change axis scale
+
+%% display a matrix (or image) 
+figure;
+imagesc(magic(15)), colorbar, colormap gray;
+% comma-chaining function calls.  
+a=1,b=2,c=3
+a=1;b=2;c=3;
+
+
+% =======================================================
+% Section 5: Octave Tutorial: For, while, if statements, and functions.
+
+v = zeros(10,1);
+for i=1:10, 
+    v(i) = 2^i;
+end
+% Can also use "break" and "continue" inside for and while loops to control execution.
+
+i = 1;
+while i <= 5,
+  v(i) = 100; 
+  i = i+1;
+end
+
+i = 1;
+while true, 
+  v(i) = 999; 
+  i = i+1;
+  if i == 6,
+    break;
+  end;
+end
+
+if v(1)==1,
+  disp('The value is one!');
+elseif v(1)==2,
+  disp('The value is two!');
+else
+  disp('The value is not one or two!');
+end
+
+% exit  % quit
+
+% Functions
+
+% Create a file called squareThisNumber.m with the following contents (without the %):
+% function r = squareThisNumber(x)
+%   r = x * x;
+% end
+
+squareThisNumber(5);  
+% If function is undefine, use "pwd" to check current directory (path), 
+% and "cd" to change directories
+pwd
+cd 'C:\Users\ang\Desktop';
+squareThisNumber(5);  
+
+% Octave search path (advanced/optional) 
+addpath('C:\Users\ang\Desktop');
+cd 'C:\'
+squareThisNumber(5);
+
+% If you have defined other functions such as costFunctionJ, 
+% the following code will work too. 
+
+X = [1 1; 1 2; 1 3];
+y = [1;2;3];
+
+theta = [0; 1]; 
+j = costFunctionJ(X, y, theta);
+
+theta = [0; 0]; 
+j = costFunctionJ(X, y, theta);
+

ipython_transcript.txt

@@ -0,0 +1,46 @@
+In [2]: 5+6  
+Out[2]: 11
+
+In [3]: 3-2    
+Out[3]: 1
+
+In [4]: 5*8  
+Out[4]: 40
+
+In [5]: 1/2  
+Out[5]: 0
+
+In [6]: 1/2.  
+Out[6]: 0.5
+
+In [7]: 2^6  
+Out[7]: 4
+
+In [8]: 2**6  
+Out[8]: 64
+
+In [9]: 1 == 2  
+Out[9]: False
+
+In [10]: 1 != 2  
+Out[10]: True
+
+In [14]: 1 and 0  
+Out[14]: 0
+
+In [15]: 1 or 0  
+Out[15]: 1
+
+In [18]: 1 ^ 0  
+Out[18]: 1
+
+In [19]: 1 ^ 1  
+Out[19]: 0
+
+In [20]: 
+
+In [20]: 0 ^ 0  
+Out[20]: 0
+
+In [21]: 
+