double

Double-precision arrays

Description

double is the default numeric data type (class) in MATLAB^®, providing sufficient precision for most computational tasks. Numeric variables are automatically stored as 64-bit (8-byte) double-precision floating-point values. For example:

x = 10;
whos x

  Name      Size            Bytes  Class     Attributes

  x         1x1                 8  double  

MATLAB constructs the double data type according to IEEE^® Standard 754 for double precision. The range for a negative number of type double is between -1.79769 x 10³⁰⁸ and -2.22507 x 10^-308, and the range for positive numbers is between 2.22507 x 10^-308 and 1.79769 x 10³⁰⁸.

For more information on double- and single-precision floating-point values, see Floating-Point Numbers.

Creation

You create a double-precision array automatically when you assign a numeric scalar or array to a variable, such as A = [1 2 3; 4 5 6]. The variable A has type double. For more information on creating and combining arrays, see Creating, Concatenating, and Expanding Matrices. In addition, operations on double-precision variables and functions with double-precision input typically return double-precision values, such as + or sin.

If you have an array of a different data type, such as single or int8, then you can convert that array to double precision using the double function, which then stores the array with more precision for further computations.

Syntax

Y = double(X)

Description

Y = double(X) converts the values in X to double precision.

Input Arguments

X — Input array

scalar | vector | matrix | multidimensional array

Input array, specified as a scalar, vector, matrix, or multidimensional array.

Data Types: single | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string

Examples

Create Double-Precision Variable

By default, numbers in MATLAB are of the data type double. You can use the class function to verify a variable's type.

x = 100;
xtype = class(x)

xtype = 
'double'

Use the double function to convert variables that are not double precision to type double.

y = true

y = logical
   1

ydouble = double(y);
ynewtype = class(ydouble)

ynewtype = 
'double'

Double-Precision Versus Single-Precision

Compare the ranges of numeric values in double-precision to the ranges for single-precision.

Use the realmin and realmax functions to display the minimum and maximum positives values that can be represented in double precision.

doublemin = realmin('double')

doublemin = 
2.2251e-308

doublemax = realmax('double')

doublemax = 
1.7977e+308

Now display the minimum and maximum positive values that can be represented in single precision. The range of values is smaller compared to double-precision, but requires less memory.

singlemin = realmin('single')

singlemin = single

1.1755e-38

singlemax = realmax('single')

singlemax = single

3.4028e+38

The eps function returns a measure of how close numbers can be in double-precision versus single-precision. Display the distance from the number 1.0 to the next larger double-precision number.

doubleeps = eps('double')

doubleeps = 
2.2204e-16

Now display the distance from 1.0 to the next larger single-precision number. Double-precision values are closer to each other, since you can represent more of them.

singleeps = eps('single')

singleeps = single

1.1921e-07

Tips

• When you are creating a class, overload double when it makes sense to convert an object of that class to a double-precision value.

• Converting a char array to a numeric type will produce an array of the corresponding Unicode^® code values. Text in strings does not convert in this way. Converting a string that does not represent a single numeric value to double will produce a NaN result. For more information, see Unicode and ASCII Values.

Extended Capabilities

Tall Arrays

Calculate with arrays that have more rows than fit in memory.

The double function fully supports tall arrays. For more information, see Tall Arrays.

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• For string inputs with misplaced commas (commas that are not used as thousands separators), generated code results can differ from MATLAB results.

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The double function fully supports GPU arrays. To run the function on a GPU, specify the input data as a gpuArray (Parallel Computing Toolbox). For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Distributed Arrays

Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Version History

Introduced before R2006a