isreal

Determine whether array uses complex storage

Syntax

tf = isreal(A)

Description

tf = isreal(A) returns logical 1 (true) when numeric array A does not have an imaginary part, and logical 0 (false) otherwise. isreal returns logical 0 (false) for complex values that have zero imaginary part, since the value is still stored as a complex number.

Examples

Determine Whether Matrix Contains All Real Values

Define a 3-by-4 matrix, A.

A = [7 3+4i 2 5i;...
     2i 1+3i 12 345;...
     52 108 78 3];

Determine whether the array is real.

tf = isreal(A)

tf = logical
   0

Since A contains complex elements, isreal returns false.

Define Complex Number with Zero-Valued Imaginary Part

Use the complex function to create a scalar, A, with zero-valued imaginary part.

A = complex(12)

A = 
12.0000 + 0.0000i

Determine whether A is real.

tf = isreal(A)

tf = logical
   0

A is not real because it has an imaginary part, even though the value of the imaginary part is 0.

Determine whether A contains any elements with zero-valued imaginary part.

~any(imag(A))

ans = logical
   1

A contains elements with zero-valued imaginary part.

Computation Resulting in Zero-Valued Imaginary Part

Define two complex scalars, x and y.

x=3+4i;
y=5-4i;

Determine whether the addition of two complex scalars, x and y, is real.

A = x+y

A = 
8

MATLAB® drops the zero imaginary part.

isreal(A)

ans = logical
   1

A is real since it does not have an imaginary part.

Find Real Elements in Cell Array

Create a cell array.

C{1,1} = pi;                 % double
C{2,1} = 'John Doe';         % char array
C{3,1} = 2 + 4i;             % complex double
C{4,1} = ispc;               % logical
C{5,1} = magic(3);           % double array
C{6,1} = complex(5,0)        % complex double

C=6×1 cell array
    {[          3.1416]}
    {'John Doe'        }
    {[2.0000 + 4.0000i]}
    {[               0]}
    {3×3 double        }
    {[5.0000 + 0.0000i]}

C is a 1-by-6 cell array.

Loop over the elements of a cell array to distinguish between real and complex elements.

for k = 1:6
x(k,1) = isreal(C{k,1});
end

x

x = 6×1 logical array

   1
   1
   0
   1
   1
   0

All but C{3,1} and C{6,1} are real arrays.

Input Arguments

A — Input array

scalar | vector | matrix | multidimensional array

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

• For numeric data types, if A does not have an imaginary part, isreal returns true; if A does have an imaginary part isreal returns false.

• For duration, calendarDuration, logical, and char data types, isreal always returns true.

• For string, table, cell, struct, datetime, function_handle, and object data types, isreal always returns false.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string | struct | table | cell | datetime | duration | calendarDuration | function_handle
Complex Number Support: Yes

Tips

• To check whether each element of an array A is real, use A == real(A).

• isreal(complex(A)) always returns false, even when the imaginary part is all zeros.

• ~isreal(x) detects arrays that have an imaginary part, even if it is all zeros.

Extended Capabilities

C/C++ Code Generation

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

Usage notes and limitations:

In the generated code, the output of isreal indicates whether the input variable or expression must be strictly real at run time. If the input could be either real or complex at run time, isreal returns false. See Code Generation for Complex Data (MATLAB Coder).

GPU Code Generation

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

Refer to the usage notes and limitations in the C/C++ Code Generation section. The same usage notes and limitations apply to GPU code generation.

HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

Thread-Based Environment

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

The isreal 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 isreal 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™.

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

Version History

Introduced before R2006a