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.

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.