EGR 106 – Week 2 – Arrays Definition, size, and terminology Construction methods Addressing and sub-arrays Some useful functions for arrays Character arrays Textbook chapter 2, pages 27-48

Recall from Last Week Variables: placeholders for numerical data – equal sign is an assignment operator c = 7.5 c = c + 1 – naming restrictions (not pi, etc. ) – can be complex valued ( x = 3 + i 7 ) Basic math on numbers and variables: + – * / ^

Uniformly Spaced Vectors Colon operator first : increment : maximum yields a row vector of equally spaced values – examples: 0 : 2 : 10 [ ] 1 : 5 [ ] 7 : -2 : -3 [ ] 1 : 2 : 8 [ ] – default for increment is 1 Note – does not hit 8!!

Arrays Fundamental data unit in Matlab – all variables are stored as arrays Data values organized into rows and columns – numeric or alphanumeric entries

Array Construction Direct specification: – Name followed by an equal sign ( = ), just like variables – List values within a pair of brackets ( [ ] ) – Enter data one row at a time left to right, top to bottom order space or comma between the values rows separated by semicolons or the enter key

Building Arrays >>a = [1 2 3; 4 5 6; 7 8 9; ] >>a = [1:3; 4:6; 7:9; 10:12]

Addressing and Sub-Arrays How to indicate a particular element within an array: – use parentheses after the array name – list desired row, comma, desired column – e.g. yield(2,4)

How About More than One Entry? Can specify a rectangular sub-array – again, use parenthesis after the array name – list desired rows, comma, desired columns as a vector, typically in brackets – e.g. yield([1 2],[3 4])

Addressing Errors

Things that do Work Single indexing of matrices counts down columns, starting at the top left

Some Useful Array Operators Transpose (single quote symbol ' ) – switches rows and columns

Useful Array Functions length(A) is the number of elements in the vector A [m n] = size(A), where A is a matrix with m rows and n columns ones(n) is an n x n matrix of ones zeros(n) is an n x n matrix of zeros

Character Arrays Rows of the array are strings of alphanumeric characters, one array entry per character Enter using a single quotation mark ( ' ) at each end