Spring Ahead! (Time Change)

Agenda 8 March 2013

Spring Ahead! (Time Change)

Test – Looks good so far!

Last Word on Structure Arrays (see below)

Recursion is a big deal

Tell Us a Story

General Says, It was a dark rainy night and the men were gathered in the mess hall after Battle, General Says, Young Colonel tell us a story

Factorials

Fibonacci

Palindrome

But how does it work (Use of a Stack)

Cafeteria

Golden Corral

What does Recursion Require?

1.  Termination Condition

2.  Call the Clone (same function)

3.  Move towards Termination Condition

****** Function fact *******

function res = fact(N)

if N < 0 || mod(N,1) > 0

error('no, not a good number...') % called a wrapper

else

res = rfact(N);

end

end

**** Real Function *****

function res = rfact(N)

% 1. have a terminating condition

if N == 0

res = 1;

else

% 2. call a clone of the original function

% vvvvv

res = N * rfact(N-1);

% ^^^

% 3. parameter(s) of that call must move towards

% the terminating condition

end

end

***** Darn those Rabbits ******* Text Chapter 9 *****

****** Fibonacci Series ******

function res = fib(N)

% Recursion of the Nth Fibonacci

if N == 1 || N == 2

res = 1;

else

res = fib(N-1) + fib(N-2);

end

end

****** Is a Palindrome *******

zerorez

never odd or even

function YesNo = isPal(str)

% recursive palindrome detector

if length(str) < 2

YesNo = true;

elseif str(1) ~= str(end)

YesNo = false;

else

YesNo = isPal(str(2:end-1));

end

end

****** Example: Structures from Spreadsheet *********

function im_really_a_script

str = get_grades('gradeSheet.xls', 2, 'L'-'A', 2);

% display the structures

for st = str

st

end

end

function stra = get_grades(name, hdrrow, cols, left)

% field names are on row 'hdrrow' of the text file:

% there are 'cols' fields to process

% there are 'left' tezxt columns to the left of the nums array

clc

% initialize the structure array to empty

[nums txt ~] = xlsread(name);

[nrows ~] = size(nums);

for student = 1:nrows

str = struct();

for col = 1:cols

% extract the field name from the header row

name = txt{hdrrow, col};

% determine if this field contains a vector

[numeric, field, ndx] = has_num(name);

% for each student

% find the row in the txt array

row = hdrrow + student;

% get a numeric value from the nums array

if numeric

value = nums(student, col - left);

% get a text value from the txt array

else

value = txt{row, col};

% if the string is empty, it's really a non-indexed number

if length(value) == 0

% so get its value from the nums array

value = nums(row - hdrrow, col - left);

end

end

% insert the value in the right place in the structure:

%

% if the field exists and is numeric, put the value

% in the correct index position in the field

if isfield(str, field)

% fetch the previous field contents

now = str.(field);

% add the new value

now(ndx) = value;

% put it back in the field

str.(field) = now;

% otherwise, just put the value whatever it is in the field

else

str.(field) = value;

end

end

stra(student) = str;

end

end

******* find a number ************

function [res, field, ndx] = has_num(name)

res = false;

field = name;

ndx = 1;

n = find(name >= '0' & name <= '9');

res = length(n) > 0;

if res

num = name(n);

ndx = str2double(num);

field = name(1:n(1)-1);

end

end