vectorization examples for efficiency

I wonder if the following expressions are already optimized forms for computational efficiency and if not how to rewrite them?

x=linspace(0,1);
0*x; x+1

a=[x;x]

[2*x;a(1,:)]

repmat([1;1;0],1,10);

Answer 1

[Walter Roberson]

x = 0:1/99:1;
zeros(size(x)); x+1
a=[x;x];
[2*x; x]
repmat([1;1;0],1,10);

[feynman feynman]

Thanks! Comparison of 0*x with zeros(size(x)) shows they are close and for 10000 loops the former becomes faster.

[Walter Roberson]

Interesting

When I try it several times, the times vary pretty wildly, including cases where the 0*x comes out much slower.

format long g
testit();
testit();
T = testit()

T = 3×1

0.000366 0.001324 0.000718

function T = testit()
   T = zeros(3,1);
   N = 10000;
   x = linspace(0,1);
   start = tic; for K = 1:N; Z = 0*x; end; T(1) = toc(start);
   start = tic; for K = 1:N; Z = zeros(size(x)); end; T(2) = toc(start);
   start = tic; for K = 1:N; Z = zeros(1,100); end; T(3) = toc(start);
end

[feynman feynman]

, which means 0*x and zeros(size(x)) aren't necessarily better or worse than the other?