Automation of for loops and array dimesion

Question

Sandeep Parameshwara 2020-1-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501498-automation-of-for-loops-and-array-dimesion

评论： Guillaume 2020-1-24

采纳的回答： Guillaume

matlab.mat

在 MATLAB Online 中打开

Hello members, I need some help.

rho_grid=[-1,0,1];
Nrho=length(rho_grid);
for i=Nrho:-1:1
    rho1=rho_grid(i);
    for j=Nrho:-1:1
        rho2=rho_grid(j);
        [U,S,V]= svd(pro(rho1,rho2));
        [Uvals(:,:,j,i),Svals(:,:,j,i),Vvals(:,:,j,i)]= svd(pro(rho1,rho2)); % I need this later for plotting
        Ti= inv(sqrt(S))*U'*Rq(rho1,rho2);
        T = Rp(rho1,rho2)*V*inv(sqrt(S));
        systrans(:,:,j,i)= ss2ss(sys.Data(:,:,j,i),Ti);
    end
end

1) I have 2 'for' loops now to determine value of parameters 'rho1' and 'rho2'. In my case, this parameters will increase to very large number. If I have rho1,....,rho10 , I dont want to create all extra for loops manually. Is there any way that I can automate it? Please note that rho_grid = [-1,0,1] is same for all parameters. Similarly,

2) The dimension of 'systrans' will also change. If I add 1 extra for loop to this I have to change from my current systrans(:,:,j,i) to

systrans(:,:,k,j,i)

which I want to avoid and automate.

3) Last question, I want plot values stored in 'Svals' over parameter range. When I had only one parameter 'rho1' I did this:

plot(rho_grid,reshape(Svals(i,i,:),[1,length(rho_grid)]));

which gave me 2D plot. for 2 parameters case, I want to get a 3D plot and see the variation of entries of Svals over rho1 and rho2. How can I do that? I have attached Uvals,Svals and Vvals in .mat file

5 个评论
显示 3更早的评论隐藏 3更早的评论

Guillaume 2020-1-23

I wouldn't use a recursion, it can all be done with a single loop. One last question, what's the size of the matrix returned by pro (or what's the size of U, S, V)? I'm assuming that it's independent of the number of rhos but if it does depend what's the formula.

It's required in order to preallocate, U_vals, S_sals, V_vals and systrans

Sandeep Parameshwara 2020-1-23

Hi Mr. Guillaume, you are right. pro is just a double matrix of size 8*8 in above case. Even though I increase number of parameters, it will be 2D matrix. I wrote Uvals(:,:,j,i) etc to store the values for each value of rho as you can see from my code.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Guillaume 2020-1-24

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501498-automation-of-for-loops-and-array-dimesion#answer_411798

在 MATLAB Online 中打开

Assumption: the matrices returned by pro, Rq, Rp, and ss2ss are all the same size (size defined by pro_outsize below

I've not changed your equations. As mentioned before inv is not recommended.

Untested code. I may have made a mistake but the princiiple should be correct:

num_rhos = 10;        %number of rho variables
rho_grid = [-1 0 1];  
pro_outsize = [8 8];  %size of matrices returned by pro, Rq, Rp and ss2ss
%create all permutation of picking num_rhos elements out of rho_grid. There's numel(rho_grid) ^ num_rhos permutations
rhoperms = cell(1, num_rhos);
[rhoperms{:}] = ndgrid(rho_grid);
rhoperms = reshape(cat(num_rhos + 1, rhoperms{:}), [], num_rhos);  %each row of rows is a unique permutation. Height of the matrix is numel(rho_grid) ^ num_rhos
%preallocation of results as 3D matrices. Can be reshape to ND matrices at the end
U_vals = zeros([pro_outsize, size(rhoperms, 1)]);
S_vals = U_vals;
V_vals = U_vals;
systrans = U_vals;
%reshape sys.Data into 3D matrix for easier indexing later on
sysdata = reshape(sys.Data, size(sys.Data, 1), size(sys.Data, 2), []);
%loop over each unique combination
for ridx = 1:size(rhoperms, 1)
    rhos = num2cell(rhoperms(ridx, :));
    [U_vals(:, :, ridx), S_vals(:, :, ridx), V_vals(:, :, ridx)] = svd(pro(rhos{:}));
    Ti = inv(sqrt(S_vals(:, :, ridx))) * U_vals(:, :, ridx)' * Rq(rhos{:});  %probably, shouldn't use inv
    T = Rp(rhos{:}) * V_vals(:, :, ridx) * inv(sqrt(S_vals(:, :, ridx)));
    systrans(:, :, ridx) = ss2ss(sysdata(:, :, ridx), Ti);
end
%Optionally: reshape into N-D matrices, where N = num_rhos + 2
newshape = [pro_outsize, repelem(numel(rho_grid), num_rhos)];
U_vals = reshape(U_vals, newshape);
S_vals = reshape(S_vals, newshape);
V_vals = reshape(V_vals, newshape);
systrans = reshape(systrans, newshape);

The code use the expansion of cell arrays into comma-separated lists to build the inputs of pro, Rq, and Rp.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Sandeep Parameshwara 2020-1-24

编辑：Sandeep Parameshwara 2020-1-24

在 MATLAB Online 中打开

Hi,

Thanks a lot for this help. It almost works. one last question, there is one problem. sys.Data is 4D data. Its '4D ss' (ss= state space) data. Hence when I reshape it it becomes 5D ss data. Hence, I decided not to do it and used sys.Data in ss2ss command. However after that I use a command in my code which takes systrans data and maps it to grid. The actual command is

sysbal=pss(systrans,rho_rgrid)

where rho_rgrid is given by the command

rho_rgrid=rgrid(rho{1},rho{2});

for 2 parameters. These are not matlab command but from external toolbox. I think below figure explains the problem. systrans is in the form systrans(:,:,1,1),systrans(:,:,2,1),...,systrans(:,:,9,1) where as I need systrans(:,:,1,1),systrans(:,:,1,2),systrans(:,:,1,3),systrans(:,:,2,1),...,systrans(:,:,3,3)

so sysbal=pss(systrans,rho_rgrid) fails and gives me the error

%Error using pss (line 71)
%Dimensions of Domain and Data are incompatible.

domain menas rho_rgrid and data is systrans. So could you please tell me how I can map it to the grid?

Thanks a lot

Sandeep Parameshwara 2020-1-24

I reshaped it using reshape(systrans,[3 3]), it works. How should I make sure that the reshaped sequence is as intended? Sorry for repeated questions.

Guillaume 2020-1-24

在 MATLAB Online 中打开

I'm not sure I completely follow, since the rhos are the same in any dimension, wouldn't (:, :, 1, 3) and (:, :, 3, 1) be the same?

You can reorder the dimensions with permute, so after the reshape, you can do:

systrans = permute(systrans, [1 2, num_rhos+2:-1:2]);

I think! It's always difficult to think in >3D. But again, I'm not sure it makes a difference.

请先登录，再进行评论。

Automation of for loops and array dimesion

5 个评论
显示 3更早的评论隐藏 3更早的评论

采纳的回答

3 个评论
显示 1更早的评论隐藏 1更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

Automation of for loops and array dimesion

5 个评论 显示 3更早的评论隐藏 3更早的评论

采纳的回答

3 个评论 显示 1更早的评论隐藏 1更早的评论

更多回答（0 个）

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

5 个评论
显示 3更早的评论隐藏 3更早的评论

3 个评论
显示 1更早的评论隐藏 1更早的评论