# Problem in unique of Constraint Randomization

**URL:** <https://verificationacademy.com/forums/t/problem-in-unique-of-constraint-randomization/31769>\
**Category:** SystemVerilog\
**Tags:** SystemVerilog, constraint, unique\
**Created:** [April 29, 2016, 5:31am UTC](https://verificationacademy.com/forums/t/problem-in-unique-of-constraint-randomization/31769 "2016-04-29T05:31:46Z")\
**Posts on this page:** 1\
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**Author:** ![sharvil111](https://verificationacademy.com/forums/user_avatar/verificationacademy.com/sharvil111/32/3790_2.png) [@sharvil111](https://verificationacademy.com/forums/u/sharvil111)\
**Post date:** [April 29, 2016, 6:49am UTC](https://verificationacademy.com/forums/t/problem-in-unique-of-constraint-randomization/31769/11 "2016-04-29T06:49:37Z")

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_In reply to [Viren\_B](https://verificationacademy.com/forums/t/problem-in-unique-of-constraint-randomization/31769/10):_

By _randc_ you can have **cyclic randomness** of a **single varaible**. While using _unique_, you can choose a **unique combination** from a **group of variables**.

```verilog
randc int a; // only variable 'a' is having unique value in randomization

rand int a,b,c;
constraint a_cn {unique {a,b,c};} // the variables a,b,c all shall have unique/different values

```

Moreover, as stated in example, using unique keyword, you can exclude some of the values from some array (use those constrained-excluded values array along with unique).

Refer [IEEE 1800-2012](https://standards.ieee.org/getieee/1800/download/1800-2012.pdf) Section 18.5.5 for more information.

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