# mustBeNegative

Validate that value is negative or issue error

## Syntax

``mustBeNegative(value)``

## Description

example

``mustBeNegative(value)` issues an error if `value` is not negative. A value is negative if it is less than zero. This function does not return a value.`mustBeNegative` accepts user-defined objects if the class of the object implements these methods:`lt``isreal``isnumeric` or `islogical`This function ignores input arguments that are empty values. Therefore, no error is thrown when the property or function argument value is empty.`

## Examples

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Use `mustBeNegative` to validate that the input contains only negative values.

The `rand` function creates uniformly distributed random numbers in the interval `(0,1)`. Test the array after the subtraction to validate that all values are negative. If not, `mustBeNegative` issues an error.

```A = rand(1,5) - 0.75; mustBeNegative(A)```
```Error using mustBeNegative (line 14) Value must be negative.```

This class restricts the value of `Prop1` to negative values.

```classdef MyClass properties Prop1 {mustBeNegative} end end```

Create an object and assign a value to `Prop1`.

```obj = MyClass; obj.Prop1 = rand(1,5) - 0.75;```
```Error setting property 'Prop1' of class 'MyClass': Value must be negative.```

When you assign a value to the property, MATLAB® calls `mustBeNegative` with the value being assigned to the property. `mustBeNegative` issues an error if the any of the elements in the array are not negative.

This function declares two input arguments. Input `lower` must be negative and input `upper` must not be negative.

```function r = mbNegative(lower,upper) arguments lower {mustBeNegative} upper {mustBeNonnegative} end x = lower*pi:upper*pi; r = sin(x); end```

Calling the function with a value for `lower` that does not meet the requirements of `mustBeNegative` results an error.

`mbNegative(0,4)`
```Error using mbNegative Invalid input argument at position 1. Value must be negative.```

## Input Arguments

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Value to validate, specified as a scalar or an array of one of the following: