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Variables in M-file Environments

Module by: Darryl Morrell

Summary: This module provides a brief introduction to the use of variables in m-file environments.

Variables

A variable is a named storage location that can be set to a particular value which can be used in subsequent computations. For example, we store a value of 5 in the variable a with the statement a=5. This value remains in a until we store a different value (for example, using the command a=100) or we clear a using the command clear a. Once a variable is set to a particular value, we can get this value by using the variable name in an expression (e.g. a/2).

Example 1

Suppose we wish to compute the circumference of a circle of diameter 5 units using the formula c = π d c π d . We could first set the variable d to a value of 5: 


>> d = 5

d =

    5.000
Then we could compute the circumference and assign its value to the variable c: 

>> c = pi*d

c =

    15.708
In this command, the product of the value of d (which is known because we earlier set it to 5) and the value of pi (which is a pre defined variable) is computed and the value of the product is stored in the variable c.

Variable names must begin with an upper- or lower-case letter. They may contain letters, digits, and underscores; they may not contain spaces or punctuation characters. Variable names are case sensitive, so A and a are different variables.

Exercise 1: Valid variable names

Which of the following are valid variable names?

  1. a
  2. B
  3. ecky_ecky_ecky_ecky_ptang_zoo_boing
  4. ecky ecky ecky ecky ptang zoo boing
  5. 2nd
  6. John-Bigboote

Solution 1

  1. Valid.
  2. Valid.
  3. Valid.
  4. Invalid, because the variable name contains spaces.
  5. Invalid, because the variable name begins with a number.
  6. Invalid, because the variable name contains a dash.

There are several predefined variables. The most commonly used include

  • ans - the default variable in which computation results are stored.
  • pi - π.
  • i or j - -1 -1 .
Once assigned, variable names remain until they are reassigned or eliminated by the clear command.

Variables can contain several types of numerical values. These types include the following:

  • Scalar - a scalar is a single value (i.e. a number). c and d in Example 1 are scalar variables.
  • Vector - a vector is an ordered series of numbers.
  • Matrices - a matrix is a rectangular array of numbers. The ability to do computations on vectors and matrices gives MATLAB its name (MATrix LABoratory).
  • strings - variables may also contain strings of characters.

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