# RealSign RealSign[x]

gives -1, 0 or 1 depending on whether x is negative, zero or positive.

# Details • RealSign is also known as sgn or signum.
• Mathematical function, suitable for both symbolic and numerical manipulation.
• RealSign[x] is equivalent to Piecewise[{{-1,x<0},{1,x>0}}].
• RealSign is piecewise constant and differentiable everywhere except at the origin.
• • RealSign tries various transformations in trying to determine the sign of symbolic expressions.
• For exact numeric quantities, RealSign internally uses numerical approximations to establish its result. This process can be affected by the setting of the global variable \$MaxExtraPrecision.
• RealSign can be used with Interval and CenteredInterval objects. »
• RealSign automatically threads over lists.

# Examples

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## Basic Examples(4)

Positive numbers:

Negative numbers:

Plot RealSign over a subset of the reals:

Derivative of RealSign:

Indefinite integral:

## Scope(28)

### Numerical Evaluation(5)

Evaluate numerically:

RealSign remains unevaluated for imaginary numbers:

RealSign always returns an infinite-precision result:

RealSign threads elementwise over lists and matrices:

RealSign can be used with Interval and CenteredInterval objects:

### Specific Values(5)

Values of RealSign at fixed points:

Value at zero:

Values at infinity:

Evaluate symbolically:

Find a value of for which the :

Visualize the result:

### Visualization(3)

Plot :

Plot RealSign along with its first derivative:

### Function Properties(10)

RealSign is only defined for real inputs:

Function range of RealSign:

RealSign is an odd function:

RealSign is not an analytic function:

It has both a singularity and a discontinuity:

RealSign is nondecreasing:

RealSign is not injective:

RealSign is not surjective:

RealSign is neither non-negative nor non-positive:

RealSign is neither convex nor concave:

### Differentiation and Integration(5)

First derivative with respect to :

Obtain an equivalent expression using the definition of derivative:

The function Sign of complex variables is not differentiable:

Its higher derivatives are equal to its first derivative:

Compute the indefinite integral using Integrate:

Definite integral:

More integrals:

## Applications(6)

Solve a differential equation with RealSign:

Compute the Fourier cosine series of RealSign:

Solve an equation involving RealSign:

Prove an inequality containing RealSign:

Simplify expressions containing RealSign:

Check orthogonality over the unit interval:

## Properties & Relations(9)

RealSign is defined only for real numbers:

Sign is defined for complex numbers:

RealSign is a differentiable function:

Sign is not differentiable:

RealSign is an integrable function:

Sign is integrable only for real arguments:

RealSign is idempotent:

Use FullSimplify to simplify expressions involving RealSign:

Definite integration:

Integral transforms:

Convert into Piecewise:

Denest:

## Possible Issues(4)

For purely real arguments, RealSign returns exact answers:

RealSign can stay unevaluated for numeric arguments: Use Simplify to obtain the sign of the expression:

Machineprecision numerical evaluation of RealSign can give wrong results: Arbitraryprecision evaluation gives the correct result: A larger setting for \$MaxExtraPrecision can be necessary:

RealSign applied to a matrix does not give the matrix sign function:

## Neat Examples(3)

Form repeated convolution integrals starting with a symmetric product of three sign functions:

Approximate RealSign through a generalized Fourier series:

Calculate rational approximations of RealSign: