docs: public static DMatrixSparseCSC symmetricPosDef( int width , int nz_total , Random rand ) {
          DMatrixSparseCSC A = rectangle(width,width,nz_total,rand);
  
          // to ensure it's SPD assign non-zero values to all the diagonal elements
          for (int i = 0; i < width; i++) {
              A.set(i,i,Math.max(0.5,rand.nextDouble()));
          }
  
          DMatrixSparseCSC spd = new DMatrixSparseCSC(width,width,0);
          CommonOps_DSCC.multTransB(A,A,spd,null,null);
  
  
          return spd;
      }