How vectorize this loop

1 次查看（过去 30 天）
Luca Re
Luca Re 2023-7-23
评论： Image Analyst 2023-7-23
x=8
a=magic(x)
b=[15 7 3 4 9 0 9 4] ====> 0 is important to test it
1 method with loop
c=a;
tic
for i=1:height(a)
for j=1:width(a)
if b(j)~=0
c(i,j)=min(a(i,j),b(j));
end
end
end
toc
tic
2 method with loop
z=a.*(~b>0)+min(a,b);
toc
isequal(c,z)
%cù
hi...I'm learning how to vectorize matrices...is it correct or can it be improved?

请先登录，再回答此问题。

采纳的回答

Bruno Luong
Bruno Luong 2023-7-23
编辑：Bruno Luong 2023-7-23
Ran in:
repmat is not needed (thanks to auto expension)
columns = 8;
a = magic(columns);
b = [15, 7, 3, 4, 9, 0, 9, 4]; % ====> 0 is important to test it
b2 = b;
b2(b2 == 0) = inf;
% Find the minimum of a or b2
minValues = min(a, b2) % What you call "c"
minValues = 8×8
15 2 3 4 9 6 7 4 9 7 3 4 9 51 9 4 15 7 3 4 9 43 9 4 15 7 3 4 9 30 9 4 15 7 3 4 9 38 9 4 15 7 3 4 9 19 9 4 15 7 3 4 9 11 9 4 8 7 3 4 4 62 9 1
  1 个评论
Image Analyst
Image Analyst 2023-7-23
@Luca Re forgot to enter his release. I don't know when auto expansion was introduced (and it's hard to find out that year in the help documentation) so I gave the version with manual expansion just to make sure he had something that worked. Of course if your version works for him, then he has a recent version and this is even more vectorized than mine.

请先登录，再进行评论。

更多回答（1 个）

Image Analyst
Image Analyst 2023-7-23
Ran in:
Sounds a lot like a homework assignment, but I'm going to assume it's not and give one possible solution:
columns = 8;
a = magic(columns);
b = [15, 7, 3, 4, 9, 0, 9, 4]; % ====> 0 is important to test it
% Fill out b so that it's a matrix the same size as a
b2 = repmat(b, [columns, 1]);
% Get rid of zeros
b2(b2 == 0) = inf
b2 = 8×8
15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4 15 7 3 4 9 Inf 9 4
% Find the minimum of a or b2
minValues = min(a, b2) % What you call "c"
minValues = 8×8
15 2 3 4 9 6 7 4 9 7 3 4 9 51 9 4 15 7 3 4 9 43 9 4 15 7 3 4 9 30 9 4 15 7 3 4 9 38 9 4 15 7 3 4 9 19 9 4 15 7 3 4 9 11 9 4 8 7 3 4 4 62 9 1
  3 个评论
显示 1更早的评论
Stephen23
Stephen23 2023-7-23
"My sokution is not correct?"
That depends: are negative values within scope?
Luca Re
Luca Re 2023-7-23
编辑：Luca Re 2023-7-23
In matrix "a" yes...in array "b" no Ok i understand...thank

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 MATLAB 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by