Update each element of multi dimensional array
显示 更早的评论
Hello!
i am working with multi dimensional arrays, and I need to check every combination of values and update them. For this pusrpose, I am using for loops but they are super slow. I have waited hours but it was still processing. Is there any faster way?
My code for 3D array is like this
for i = 1:nrows
for j = 1:ncols
for k = 1:ndepths
AI = function(a(i), b(j), c(k));
cspace (i,j,k) = JKM(AI);
end
end
end
18 个评论
madhan ravi
2019-4-4
upload you function and the values to test
bilal javed
2019-4-4
编辑：bilal javed
2019-4-5
"I am working on problem where cspace might be 6 or 7 dimensional. But I am stuck with 3D case"
Then you need to vectorize your function.
Remember that each nested loop multiplies the total number of iterations by its own number of iterations, so six or seven loops will require calling your function 360^6 or 360^7 times. Unless your function is exceptionally fast, this will take some time.
bilal javed
2019-4-4
Jos (10584)
2019-4-4
Why do you need all combinations? What are you going to do with them?
Guillaume
2019-4-4
If this is exactly how you preallocate cspace:
cspace = true(nrows*ncols*ndepths);
Then it is not preallocated correctly. it has way too many rows and columns, and only one page, which will grow at each k step. You'll end up with a nrows*ncols*ndepth x nrows*ncols*ndepth x ndepth which will have been unnecessary copied ndepth-1 times.
Proper preallocation would be:
cspace = true(nrows, ncols, ndepths);
"But I have no idea how to vectorize my function"
How you'd vectorise the function depends entirely on what the function does. Some functions cannot be vectorised. Without more details, we can't really help you.
madhan ravi
2019-4-4
bilal javed
2019-4-5
Guillaume
2019-4-5
As Madhan said, we need to see the code for that JKM function. From the sound of it, it is probably complex enough that it may not be possible to vectorise it.
bilal javed
2019-4-17
编辑：bilal javed
2019-4-17
Jan
2019-4-17
While clear is usually less useful than the programmer thinks, letting an array grow iteratively is very inefficient. So avoid cspace = [cspace, collide], but pre-allocate.
If you write "OUT OF MEMORY after 1st iteration", which line does this mean exactly? The less the readers have to guess, the better.
Guillaume
2019-4-17
I assume the clear are an attempt to save memory. Most of the variables you clear use very little memory so it's a waste of time. The largest matrix in the code you show is cspace_coords which only requires 135 MB of memory.
These matrices are not the cause for the low memory.
In any case, as Jan says we need to know the line where the error occur.
I would replace this lot:
nrows = length(theta1_range);
ncols = length(theta2_range);
ndepths = length(theta3_range);
[TH1, TH2, TH3] = ndgrid(theta1_range,theta2_range,theta3_range);
THETA1 = TH1(:);
THETA2 = TH2(:);
THETA3 = TH3(:);
l = length(THETA1);
clear TH1 TH2 TH3
cspace_coords = [THETA1, THETA2, THETA3];
clear THETA1 THETA2 THETA3 theta1_range theta2_range theta3_range
by:
cspace_coords = zeros(numel(theta1_range), numel(theta2_range), numel(theta3_range), 3);
[cspace_coords(:, :, :, 1), cspace_coords(:, :, :, 2), cspace_coords(:, :, :, 3)] = ndgrid(theta1_range, theta2_range, theta3_range)
cspace_coords = reshape(cspace_coords, [], 3);
Bilal Javed
2019-4-17
编辑：Bilal Javed
2019-4-17
I am using matlab 2018b. wndows 10, intel corei7, 16 gb ram, 250 gb ssd, 1 tb hdd, nvidia 4gb graphic card
Walter Roberson
2019-4-17
[patch(obstacle1), patch(obstacle2),patch(obstacle3)] look like array indexing that could be done ahead of time.
per isakson
2019-4-17
As Jan said, avoid cspace = [cspace; collide];
Guillaume
2019-4-18
The error message tells you the out of memory occurs in the parfor. So, it all depends on that GJK function for which you haven't shown the code.
What's the output of memory before you execute the parfor loop? By far, the biggest variable is your fv which uses ~4.5 GB of memory.
Walter Roberson
2019-4-18
I just noticed that your fv is a struct with fields face and vertices. That suggests that you are creating four patch objects for each of your 296487 struct array elements, and that those form parameters to whatever GJK does. That is a lot of graphics objects, over 72 million verticles for the fv alone, and unknown numbers of graphics elements triggered by the obstacle patches.
Note that graphics objects created on parallel workers cannot change the display: parallel workers are different processes that work independently without connection to the graphics display thread.
回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
2019-4-4
2019-4-18
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
