Interpreter. Computational time
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Hello, All! We have found some interesting moment. 1. If we use to call next function:
function [result,time] = Func(x,y,u)
N = size(x,1);
M = size(y,1);
result = zeros(M,1);
tic;
for j=1:M
for i=1:N
result(j) = result(j) + u(i) / ( y(j) - x(i) );
end;
end;
time = toc;
we obtain time = 1.9sec.
2. If we use
N = length(x,1);
M = length(y,1);
or use to call next function:
function [result,time] = Func(x,y,u,N,M)
result = zeros(M,1);
tic;
for j=1:M
for i=1:N
result(j) = result(j) + u(i) / ( y(j) - x(i) );
end;
end;
time = toc;
we obtain time = 3.0sec.
3. But if we place the function body into the program body we obtain time = 3.7sec.
4. Besides, if we call this function in a cycle then computational time of each function increased.
Time data averaged by 10 runs for random x,y,u. If we measure time outside the functions (or time of the functions executions) we obtain the same time. Can anybody explain why it is happening?
P.s. We use Matlab 2009b and 2010b and test this on different workstations.
回答（1 个）
Matt Fig
2011-5-12
SIZE and LENGTH are not the same thing!
size(rand(2,10000),1)
length(rand(2,10000))
You should show what your data looks like, i.e., what does:
size(x)
size(y)
show?
4 个评论
Dmitry Maryin
2011-5-12
Dmitry Maryin
2011-5-12
Sean de Wolski
2011-5-12
N = length(x,1);
Should throw an error unless you've overwritten function length
Dmitry Maryin
2011-5-12
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