function priority1
% ***************************************************************
% * This program shows the importance of performing arithmetic  *
% * operations in the right order.                              *
% * y2 and y3 should be identical.                              *
% * y1 should differ and be more accurate.                      *
% ***************************************************************
  format compact
  n=1000;
  A=randn(n);
  B=randn(n);
  x=randn(n,1);
%
  tic
  y1=A*(B*x);  
  t1=toc
%
  tic
  y2=A*B*x;
  t2=toc
%
  tic
  y3=(A*B)*x;  
  t3=toc
%
  check12=norm(y1-y2)/norm(y1)
  check13=norm(y1-y3)/norm(y1)
%
  tic
  y4=-(A*x);
  t4=toc
%
  tic
  y5=-A*x;
  t5=toc
%
  tic
  y6=0-A*x;
  t6=toc
%
  tic
  y7=0.0-A*x;
  t7=toc
%