docs: public static void constraintMatrix3x3a( DMatrixRMaj L_3x6 , DMatrixRMaj L_3x3 ) {
  
  		int index = 0;
  		for( int i = 0; i < 3; i++ ) {
  			L_3x3.data[index++] = L_3x6.get(i,0);
  			L_3x3.data[index++] = L_3x6.get(i,1);
  			L_3x3.data[index++] = L_3x6.get(i,2);
  		}
  	}