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# 4. Numeric Data Types

A numeric constant may be a scalar, a vector, or a matrix, and it may contain complex values.

The simplest form of a numeric constant, a scalar, is a single number that can be an integer, a decimal fraction, a number in scientific (exponential) notation, or a complex number. Note that by default numeric constants are represented within Octave in double-precision floating point format (complex constants are stored as pairs of double-precision floating point values). It is however possible to represent real integers as described in Integer Data Types. Here are some examples of real-valued numeric constants, which all have the same value:

 ```105 1.05e+2 1050e-1 ```

To specify complex constants, you can write an expression of the form

 ```3 + 4i 3.0 + 4.0i 0.3e1 + 40e-1i ```

all of which are equivalent. The letter ‘i’ in the previous example stands for the pure imaginary constant, defined as `sqrt (-1)`.

For Octave to recognize a value as the imaginary part of a complex constant, a space must not appear between the number and the ‘i’. If it does, Octave will print an error message, like this:

 ```octave:13> 3 + 4 i parse error: syntax error >>> 3 + 4 i ^ ```

You may also use ‘j’, ‘I’, or ‘J’ in place of the ‘i’ above. All four forms are equivalent.

Built-in Function: double (x)

Convert x to double precision type.

Built-in Function: complex (x)
Built-in Function: complex (re, im)

Return a complex result from real arguments. With 1 real argument x, return the complex result `x + 0i`. With 2 real arguments, return the complex result `re + im`. `complex` can often be more convenient than expressions such as `a + i*b`. For example:

 ```complex ([1, 2], [3, 4]) ⇒ 1 + 3i 2 + 4i ```

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