vectorizing or speeding looped code

2020 9 22
1 个回答
更新时间：2026 2 4
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0 个投票

i am trying to speed up some code with multiple functions and have found the one that takes the most time (it is all a converted fortran code). it runs a nested for loop 4 times (each with modified input). i've had some success elsewhere in the code eliminating slow points but this one just cant get right. any ideas? (in 2016b for compatability reasons)
for II= 1:N
XP(1)= 1.0D0;
for JJ=2:IORD1
XP(JJ)=XP(JJ-1)*double(A1(II));
end
for JJ= 1:IORD1
for KK= 1:IORD1
B(JJ,KK)=B(JJ,KK)+XP(JJ)*XP(KK);
end
C(JJ)=C(JJ)+XP(JJ)*A2(II);
end
end

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回答（1 个）

Turlough Hughes
Turlough Hughes 2020-9-22

0 个投票

This should help, though I've already made assumptions about the sizes of arrays. How many rows/columns are in each variable?
XP(1) = 1;
for II= 1:N
XP(2:end) = XP(1:end-1)*double(A1(II));
B = B + XP(:).*XP(:).';
C = C + XP*A2(II);
end

10 个评论
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Paul Schenk
Paul Schenk 2020-9-22
the dimensions change (get smaller) in each of the 4 runs. they will have to be declared each time.
Turlough Hughes
Turlough Hughes 2020-9-22
Did the code work?
Some questions: is XP a column vector/row vector? Does A2 have as many elements as XP? Also, does B contain IORD1 rows and columns? Similarly does C have IORD1 elements?
Paul Schenk
Paul Schenk 2020-9-22
移动：Rik 2026-2-4
not as entered. tripled cpu time.
here are preallo's to variables:
ORDER_MAX = 20;
C = zeros(ORDER_MAX+1,1);
IORD=MAXOR;
IORD1=IORD+1;
B = single(zeros(ORDER_MAX+1,ORDER_MAX+1)); % Solution matrix
XP = double(zeros(ORDER_MAX+1,1)); % Array of solutions
Paul Schenk
Paul Schenk 2020-9-22
移动：Rik 2026-2-4
a1 and a2 are linear (1,2000) arrays that are usually only 10% filled in.
Turlough Hughes
Turlough Hughes 2020-9-23
移动：Rik 2026-2-4
Vectorisation is usually faster but not always. Probably best to just provide a minimum working example (google it) of code that I (or others) can test and profile. Otherwise it really is just guess work.
Paul Schenk
Paul Schenk 2020-9-23
移动：Rik 2026-2-4
hope this works for you. it is essentially a customized LS fit solution.
Turlough Hughes
Turlough Hughes 2020-9-23
移动：Rik 2026-2-4
Can you give some typical inputs aswell?
Paul Schenk
Paul Schenk 2020-9-23
移动：Rik 2026-2-4
example:
eqor=1, n=222 and a1 and a2 are linear vectors of numbers N long (they change each time and can be random for this test)
Turlough Hughes
Turlough Hughes 2020-9-23
移动：Rik 2026-2-4
eqor=1 ? I assume that's MAXOR?
Paul Schenk
Paul Schenk 2020-9-23
移动：Rik 2026-2-4
yes, my mistake!

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