Sped up for loop

2016 2 23
1 个回答
更新时间：2021 8 20
2 次查看（30 天）

0 个投票

Dear all,
Please show me how to speed up the for loops below. It took me a day to run for M=50.
I would appreciate your help! Best, Dat
clear all;
clc;
M = 20;
A_pro_cct = zeros(16,M);
tm = zeros(16,16);
s = zeros(17,4);
for N = 1:M
for ii = 1:N
filename = 'C:\Users\Dat\Documents\CT_TMs_counties.xlsx';
sheet = ii;
tm = xlsread(filename,sheet,'b2:q17');
s = xlsread(filename,sheet,'h21:k37');
for i = 1:16
pro_cct = s(i,1)*tm(i,9)+tm(i,3)*s(i,3) + tm(i,1)*s(i,1);
A_pro_cct (i,N) = pro_cct;
end
end
end
AA = A_pro_cct';

回答（1 个）

Steven Lord
Steven Lord 2016-2-23

0 个投票

You're reading the Microsoft Excel spreadsheet file M*(M+1) times in your double nested FOR loop. Instead pull those lines of code outside the double FOR loops, read the file into a variable once (or once per sheet) and refer to the appropriate section of that variable inside the loop.

5 个评论
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Dat Tran
Dat Tran 2016-2-23
Thank you for promptly response! I have tried to do as below but results was only saved for the last input.
clear all; clc;
N = 2; A_pro_cct = zeros(16,N);
for ii = 1:N filename = 'C:\Users\Dat\Documents\CT_TMs_counties.xlsx'; sheet = ii; tm{ii} = xlsread(filename,sheet,'b2:q17'); s{ii} = xlsread(filename,sheet,'h21:k37'); end
for ii = 1:N for i = 1:16 pro_cct = s{ii}(i,1)*tm{ii}(i,9)+tm{ii}(i,3)*s{ii}(i,3) + tm{ii}(i,1)*s{ii}(i,1); A_pro_cct (i,N) = pro_cct;
end end AA = A_pro_cct';
Dat Tran
Dat Tran 2016-2-23
编辑：Jan 2016-2-23
I found how to save the results but the loop does take quite a bit of time!
clear all;
clc;
N = 10;
A_pro_cct = zeros(16,N);
for ii = 1:N
filename = 'C:\Users\Dat\Documents\CT_TMs_counties.xlsx';
sheet = ii;
tm{ii} = xlsread(filename,sheet,'b2:q17');
s{ii} = xlsread(filename,sheet,'h21:k37');
end
for M = 1:N
for ii = 1:M
for i = 1:16
pro_cct = s{ii}(i,1)*tm{ii}(i,9)+tm{ii}(i,3)*s{ii}(i,3) + tm{ii}(i,1)*s{ii}(i,1);
A_pro_cct (i,M) = pro_cct;
end
end
end
AA = A_pro_cct';
Jan
Jan 2016-2-23
编辑：Jan 2016-2-23
Please format your code using the "{} Code" button, such that it is readable. Thanks.
Omit te time consuming clear all, because it removes all loaded functions from the memory. Reading them from the slow hard disk wastes time.
Dat Tran
Dat Tran 2016-2-24
Thank a lot!!!
Image Analyst
Image Analyst 2016-2-24
As I understand it, if you have R2015b or later, the Excel reading will be a lot faster because it does not shutdown the Excel server after xlsread(), and so does not have to launch it again either.
And cell arrays take a huge amount of memory and a lot of overhead. You don't even need to use cell arrays at all. Just use regular numerical arrays.

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Dat Tran
Dat Tran
2016-2-23

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2021-8-20

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