It is faster to index an initialized matrix or use a tunnel auto-indexed, both inside a loop - what happens?

WARNING: MATLAB user here.

Note: This is a question of LabVIEW, not a matter of MathScript.  I just use MathScript to demonstrate the point.

This is background to the particular question.

In MATLAB if you want to calculate decent efficiency then you want previously declared tables and want the built-in functions.

This means that it's slow:

ICT

for i = 1: 10000

ENTRIES = rand;

end

T1 = toc

(t1 = 0.266, so 37.6 elements/MS)

and it's faster

% start before the next loop, but not copy - paste with it because it slows down it waaaay

Claire x

ICT

x = Zeros (10000,1);  % If not the ', 1' and then it overflows of memory to MathScript

for i = 1: 10000

ENTRIES = rand;

end

T2 = toc

(t2 = 0.205, items so 48.8/MS)

In MathScript, it is an improvement of 23% at run time.

ratio = 100 *(t2-t1)/t1

(ratio = - 23.3)

When I use LabVIEW for the same thing, I get:

which leads to a computation time of 269 ms for about 10 000 000 elements in a vector.  (Note that this is literally ~ 1000 x faster than MathScript).  He created elements of k ~ 37 per millisecond.

If I change out for a created matrix indexing, then the time is strange.

When I run it for 10 elements of k, or about 1000 times less, then he finished in approximately 30ms, or approximately 333 items per millisecond.

When I run it for 100 k items, or about 10 x more last run and 100 x less than the previous vi, and then it ended with about 5000 ms, or approximately 20 items per millisecond.

The best construction and replace it is running hundreds of times slower, and it is perhaps running ~ 1800 x slower.

Here's my problem:

One of these things is 1800 x slower than others.  Why is it reasonable?  Why is-111 x reasonable?  Here are the simple changes.

I love that LabVIEW is literally 1000 x faster than MatLab in certain tasks.  I need to understand why, in some cases this multiplier 1000 x falls down to a 2. 4 x DECREASE.  Intuition I have is not only wrong, it's incredibly bad.  He's wasting the 1000 x multiplier of speed that I am very happy with.

My thought:

If I did it in assembler to nickname the first loop is as follows.

I point to the stack, call the random number generator to get a value on the stack, incrementing my counter, check if it's 10 million, update my pointer location and iterate.

The second loop would be as follows:

Point battery, I write a zero, incrementing my counter, test whether it is 10 million, update my pointer location and iterate.

then

I will return to the beginning of the location of the stack, call the generator of random numbers to get a value on the stack, incrementing my counter, check if it's 10 million, update my pointer location and iterate.

The report of the runtime for loops would be the time difference of calculation-writing-increment of a (pseudo) random number and THEN a zero against writing incrementing from zero.  I expect it to be somewhere between 2 x and 10 x.

There are BONES.  Perhaps the algorithm to calculate a random number has many steps, like thousands.  Here is the difference between On-die, L2, RAM and disk.  Given enough items I would expect things to have to go through the bottlenecks and get slow.

You have to shift registers when using him in place element structure. I don't know why, but it is much faster (and a more exact comparison) when you use the shift register.

Tags: NI Software

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