Constants and Variables

Constants

MATLAB provides some internal constants, as shown in Table 2-1. These constants define data frequently used in MATLAB applications and programming, such as calculation precision, pi, etc.

Table 2-1: Internal Constants Provided by MATLAB

The constants listed in Table 2-1 can be used directly in MATLAB programming without declaration.

[Example 2-1] Enter some command lines with constants in the Command Window and observe the calculation results.

a = abs(3+4i)
a =
     5
z = sqrt(besselk(4/3,rho-i))
z =
   0.3730 + 0.3214i
huge = exp(log(realmax))
huge =
  1.7977e+308
toobig = pi*huge
toobig =
   Inf

Variables

1. Variable Names

The first character of a MATLAB variable name must be a letter, followed by any combination of letters, digits, and underscores.

Note: Variable names in MATLAB are case-sensitive, so A and a are different variables.

Although there is no limit to the length of a variable name, MATLAB only uses the first N characters of the variable name, ignoring the rest. Here, N is the return value of the function namelengthmax. Therefore, it is important to make the first N characters of the variable name unique so that MATLAB can distinguish between different variables.

N = namelengthmax
N =
    63

You can use the isvarname function to confirm the validity of a variable name. If the variable name is valid, the function returns 1; otherwise, it returns 0.

[Example 2-2] Enter the following in the Command Window:

isvarname 8th_column
ans =
     0

Since the first character of the variable name above is 8, which is invalid, it returns 0.

Note: MATLAB uses the characters i and j to represent the imaginary unit. If you are involved in complex number calculations, you should avoid using i and j as variable names.

MATLAB reserves some keywords and does not allow them to be called. If they are used in a call, it may result in error messages like the following:

Error: Expected a variable, function, or constant, found "=".

Error: "End of Input" expected, "case" found.

Error: Missing operator, comma, or semicolon.

Error: "identifier" expected, "=" found.

Use the iskeyword function without input variables to list all reserved keywords.

2. Creating Variables

Creating variables in MATLAB is simple: you do not need to declare the data type of the variable.

[Example 2-3] Enter the following command line in the Command Window to create a variable A:

A=9
A =
     9

Note: Before assigning the value of a variable to another variable, you must ensure that the variable on the right side of the equation has a value; otherwise, an error will be returned. For example, in the following statement, variable a has no value.

A=a
Undefined function or variable 'a'.

If a variable already exists, assigning a value to it will replace its current value.

3. Data Types of Variables

MATLAB provides more than ten types of data, as shown in Figure 2-1. However, all MATLAB variables, regardless of their type, are stored in the form of arrays or matrices. A matrix is the two-dimensional version of an array.

Figure 2-1: Data Types Provided by MATLAB

Table 2-2 summarizes the various data types in MATLAB.

Table 2-2: Data Types in MATLAB

In MATLAB, when performing numerical calculations, all variables default to the double type. Use the format command to set the output format of variables.

[Example 2-4] Enter the following command line in the Command Window to create the variable VarFormat:

VarFormat=10.1892
VarFormat =
   10.1892

To output the variable value in a 15-digit fixed-point format, enter in the command line:

format long
VarFormat

Returns:

VarFormat =
  10.189200000000000

To output the variable value in a 15-digit floating-point format, enter in the command line:

format long e
VarFormat

Returns:

VarFormat =
  1.018920000000000e+01

To output the variable value in hexadecimal, enter in the command line:

format hex
VarFormat

Returns the variable value:

VarFormat =
   402460ded288ce70