Randomize an matrix with negative number constraints

SystemVerilog
1

Problem: I want to create a 2x2 matix with positive and negative numbers. the sum of positive numbers should be less than 7 and sum of negative numbers should be greater than -8.

But i only get 0’s when i print the matix, code is below please let me know if i am missing anything.

class mem;
  rand int mat[2][2];

  rand int p_cnt,n_cnt;
  
  constraint c_size
  {
    
    foreach(mat[row,col])
    {   
      mat[row][col] inside {[-8:7]}; 
      if(mat[row][col][3])
      {
        n_cnt==n_cnt+mat[row][col];
      }
      else
        p_cnt == p_cnt+mat[row][col];
       
            
    }
        p_cnt <7;
        n_cnt > -8;
  }
2

In reply to CRVAddict:
The way you wrote the constraint, 0’s are the only solution. I think you want

 constraint c_size
  {
    foreach(mat[row,col]) 
      mat[row][col] inside {[-8:7]}; 
    mat.sum(D1) with (D1.sum(D2) with (D2 >=0 ? D2 : 0) ) <  7;
    mat.sum(D1) with (D1.sum(D2) with (D2 < 0 ? D2 : 0) ) > -8;
 }
endclass

BTW, the sum() method only works for one dimension, that why I nested the methods.

3

In reply to dave_59:

Hi Dave,

I am getting the following error, when i tried your code.

mat.sum(D1) with( D1.sum(D2) with (D2 >=0 ? D2:0) ) < 7;

Randomization constraint has this error, which will cause the randomize function to return 0 and no new rand values will be set:
Unsupported operator ‘sum over upper dimension of multi-dimensional array’ in this constraint expression.
mem_inst.randomize();
|

4

In reply to CRVAddict:

Unsupported means your tool recognizes the construct, but does has not implemented support for it.

You need to choose a different simulator, or convert your array to one dimension, and calculate the index from row/col manually.