sign

Sign function (signum function)

Syntax

sign(x)

Description

Y = sign(x) returns an array Y the same size as x, where each element of Y is:

• 1 if the corresponding element of x is greater than 0.

• 0 if the corresponding element of x equals 0.

• -1 if the corresponding element of x is less than 0.

• x./abs(x) if x is complex.

Examples

Find Sign Function

Find the sign function of a number.

sign(2)

ans = 
1

Find the sign function of the values of a vector.

V = [-11 0 1.5 Inf NaN];
sign(V)

ans = 1×5

    -1     0     1     1   NaN

Find the sign function of the values of a matrix.

M = magic(3) - 5;
sign(M)

ans = 3×3

     1    -1     1
    -1     0     1
    -1     1    -1

Find the sign function of a complex number.

z = 4 - 3*i;
sign(z)

ans = 
0.8000 - 0.6000i

Plot Sign Function

Plot the sign function and show its behavior at the zero-crossing. Use eps to represent values just above and below 0.

x = [-5 -eps(1) 0 eps(1) 5];
y = sign(x);
plot(x,y)
ylim([-2 2])
grid on

Plot Real and Imaginary Parts of Sign Function

Plot real and imaginary parts of the sign function over $$-3<x<-3$$ and $$-3<y<3$$.

First, create a mesh of values over -3 < x < 3 and -3 < y < 3 using meshgrid. Then create complex numbers from these values using z = x + 1i*y.

v = -3:0.1:3;
[x, y] = meshgrid(v);
z = x + 1i*y;

Find the real and imaginary parts of the sign function of z.

s = sign(z);
re = real(s);
im = imag(s);

Plot the real and imaginary parts.

surf(x,y,re)
title('Real part of sign function')
xlabel('x')
ylabel('y')

figure(2)
surf(x,y,im)
title('Imaginary part of sign function')
xlabel('x')
ylabel('y')

Input Arguments

x — Input

scalar | vector | matrix | multidimensional array

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

If an element of x is NaN, then sign returns NaN in the corresponding element of the output.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | duration
Complex Number Support: Yes

Extended Capabilities

Tall Arrays

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

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

C/C++ Code Generation
Generate C and C++ code using MATLAB® 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 sign 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