请更有效的Matlab代码 [英] More efficient Matlab Code please
问题描述
我是matlab的新手,所以我不知道matlab为使代码更高效,更快而必须具备的所有快捷方式.我一直在matlab上为家庭作业分配一些东西,同时专注于完成分配而不是效率.现在,我发现我花在等待程序上的时间比实际编码要花费更多的时间.下面是嵌套for循环的麻烦,它需要永远地完成.没有这么多的forloop,有没有一种更快或更有效的编码方式?
I am new to matlab so I do not know all the shortcuts matlab has to make the code more efficient and faster. I have been hacking together something in matlab for a homework assignment while focusing on completing the assignment rather than efficiency. Now I'm finding that I'm spending more time waiting on the program than actually coding it. Below is a headache of nested for loops that takes forever to finish. Is there a faster or efficient way of coding this without so many forloops?
for i = 1:ysize
for j = 1:xsize
MArr = zeros(windowSize^2, 2, 2);
for i2 = i - floor(windowSize/2): i + floor(windowSize/2)
if i2 > 0 && i2 < ysize + 1
for j2 = j - floor(windowSize/2): j + floor(windowSize/2)
if j2 > 0 && j2 < xsize + 1
mat = weight*[mappedGX(i2,j2)^2, mappedGX(i2,j2)*mappedGY(i2,j2); mappedGX(i2,j2)*mappedGY(i2,j2), mappedGY(i2,j2)^2];
for i3 = 1:2
for j3 = 1:2
MArr(windowSize*(j2-(j - floor(windowSize/2))+1) + (i2-(i - floor(windowSize/2)) + 1),i3,j3) = mat(i3,j3);
end
end
end
end
end
end
Msum = zeros(2,2);
for k = size(MArr)
for i2 = 1:2
for j2 = 1:2
Msum = Msum + MArr(k,i2,j2);
end
end
end
R(i,j) = det(Msum) - alpha*(trace(Msum)^2);
R = -1 * R;
end
end
推荐答案
使用冒号代替循环.例如:
Instead of looping, use colons. For example:
for i3 = 1:2
for j3 = 1:2
MArr(windowSize*(j2-(j - floor(windowSize/2))+1) + (i2-(i - floor(windowSize/2)) + 1),i3,j3) = mat(i3,j3);
end
end
可以写为:
MArr(windowSize*(j2-(j-floor(windowSize/2))+1)+(i2-(i-floor(windowSize/2))+1),:,:)=mat;
找到所有可以做到的地方后,学习使用索引而不是循环,例如,
After you find all places where this can be done, learn to use indexing instead of looping, e.g.,
i2 = i - floor(windowSize/2): i + floor(windowSize/2);
i2=i2(i2>0 && i2<ysize+1);
j2 = j - floor(windowSize/2): j + floor(windowSize/2);
j2=j2(j2>0 && j2<xsize+1);
mat = weight*[mappedGX(i2,j2)^2, mappedGX(i2,j2)*mappedGY(i2,j2);
(高级用户注意:如果mappedGX
是矩阵,并且i2
/j2
不代表矩形子矩阵,则最后一行可能不起作用.在这种情况下,您将需要
(Note for advanced users: the last line may not work if mappedGX
is a matrix, and i2
/j2
don't represent a rectangular sub-matrix. In such a case you will need sub2ind()
)
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