1. Working with Arrays in MATLAB
Chapter 3 MATLAB Fundamentals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Review: Scalars and Arrays
In a spreadsheet, we do not need to name every variable: the cell address (row/column) defines the storage location
Storage locations for time and displacement values
Engineering Computation: An Introduction Using MATLAB and Excel

3. Arrays
In MATLAB and other programming languages, the variables must be named and storage of results must be planned
An array is a variable that has multiple values
An array’s name is followed by an index (or indices, for multi-dimensional arrays) in parentheses
Engineering Computation: An Introduction Using MATLAB and Excel

4. Indices of Arrays Think of the index value as an address
Important: Indices must be positive integers, and must start with one
Example: To store these results, we would define
t(1) = 0, t(2) = 0.1, t(3) = 0.2…
y(1) = 3, y(2) = …
Engineering Computation: An Introduction Using MATLAB and Excel

5. Common Mistakes Using Indices with MATLAB
Using an index of zero:
Using an index not an integer: setting t(0.1) equal to a value results in the same error as above
Engineering Computation: An Introduction Using MATLAB and Excel

6. Common Mistakes Using Indices with MATLAB
Progressing indices by values other than 1. For example, if we take a temperature reading every 10 seconds, and set the first value as T(10), then zeros are filled in for the first nine values of T:
(No error is reported, but this result is probably not what is desired)
All of these errors result from confusion between independent variables and indices. Thinking of indices as addresses helps avoid these errors
Engineering Computation: An Introduction Using MATLAB and Excel

7. Multi-Dimensional Arrays
A variable may have more than one index. A two-dimensional array is similar to the data storage of a spreadsheet. Instead of a row number and a column letter, a two-dimensional array has two index numbers
Examples: t(1,5) R(3,3) temp(1,20)
Efficient way to store data: if both indices range from 1-10, then the number of values stored is X 10 = 100
Engineering Computation: An Introduction Using MATLAB and Excel

8. Matrices One- and two-dimensional arrays are also called matrices
Many mathematical operations can be performed with matrices - the name MATLAB comes from “Matrix Laboratory”
The size of a matrix is defined by the numbers of rows and columns. Example; a 3 X 2 matrix:
Engineering Computation: An Introduction Using MATLAB and Excel

9. Vectors One-dimensional matrices are referred to in MATLAB as vectors
Vectors can be classified as column vectors (all values arranged in a single column) or row vectors (all values arranged in a single row)
Caution: in mechanics classes, the term “vector” has a different definition: a vector is defined as a physical quantity which is defined by magnitude and direction
Engineering Computation: An Introduction Using MATLAB and Excel

10. Entering Arrays in MATLAB
Consider the matrix:
To enter this matrix in MATLAB: or
Commas or spaces separate elements within a row, semi-colons separate rows
Engineering Computation: An Introduction Using MATLAB and Excel

11. Arrays
We will work with matrix math later, with applications such as solving simultaneous equations
We will create large arrays of results using programming loops. Loops control the execution of repetitive calculations, and the results are often stored in arrays
Engineering Computation: An Introduction Using MATLAB and Excel