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其他 - 用于分叉的MATLAB并行池

发布于 2020-03-27 16:14:01

我对MATLAB(我使用的是2019 a版本)和编码的并行池这个概念不熟悉。我将与您共享的该代码可以在网上找到,并做了一些修改以满足我的要求。

Problem Statement: I'm having a non-linear system (Rossler equation) & I have to plot its Bifurcation diagram, I tried to do it normally using for loop but its computation time was too much and my computer got hanged several times, so I got an advice to parallel pool my code in order to come out of this problem. I tried to learn how to parallel pool using MATLAB on the net but still I'm not able to resolve my Issues as there are still some problems since there are 2 parfor loops in my code I'm having problems with Indexing and in assignment of the global parameter (Please note: This code is written for normal execution without using parallel pooling).

I'm attaching my code below here, please excuse if I've mentioned a lot many lines of codes.

clc;
a = 0.2; b = 0.2; global c;
crange = 1:0.05:90; % Range for parameter c
k = 0; tspan = 0:0.1:500; % Time interval for solving Rossler system
xmax = []; % A matrix for storing the sorted value of x1

for c = crange
f = @(t,x) [-x(2)-x(3); x(1)+a*x(2); b+x(3)*(x(1)-c)];
    x0 = [1 1 0]; % initial condition for Rossler system 
    k = k + 1;
    [t,x] = ode45(f,tspan,x0); % call ode() to solve Rossler system
    count = find(t>100); % find all the t values which is >10  
    x = x(count,:);
    j = 1; 
    n = length(x(:,1)); % find the length of vector x1(x in our problem)

    for i=2 : n-1
       % check for the min value in 1st column of sol matrix
       if (x(i-1,1)+eps) < x(i,1) && x(i,1) > (x(i+1,1)+eps)  
           xmax(k,j)=x(i,1); % Sorting the values of x1 in increasing order
           j=j+1;
       end 
    end

    % generating bifurcation map by plotting j-1 element of kth row each time
    if j>1
        plot(c,xmax(k,1:j-1),'k.','MarkerSize',1);
    end 

    hold on;
    index(k)=j-1;    
end
xlabel('Bifuracation parameter c');
ylabel('x max');
title('Bifurcation diagram for c'); 

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提问者
akhil krishnan
被浏览
43
Edric 2020-01-31 17:08

This can be made compatible with parfor by taking a few relatively simple steps. Firstly, parfor workers cannot produce on-screen graphics, so we need to change things to emit a result. In your case, this is not totally trivial since your primary result xmax is being assigned-to in a not-completely-uniform manner - you're assigning different numbers of elements on different loop iterations. Not only that, it appears not to be possible to predict up-front how many columns xmax needs.

Secondly, you need to make some minor changes to the loop iteration to be compatible with parfor, which requires consecutive integer loop iterates.

因此,主要的变化是使循环将结果的各行写入我称为的单元格数组中xmax_cellparfor循环之外,将其转换回矩阵形式很简单。

综上所述,我们最终得出结论,据我所知,它在R2019b中正常工作:

clc;
a = 0.2; b = 0.2;
crange = 1:0.05:90; % Range for parameter c
tspan = 0:0.1:500; % Time interval for solving Rossler system

% PARFOR loop outputs: a cell array of result rows ...
xmax_cell = cell(numel(crange), 1);
% ... and a track of the largest result row
maxNumCols = 0;

parfor k = 1:numel(crange)
    c = crange(k);
    f = @(t,x) [-x(2)-x(3); x(1)+a*x(2); b+x(3)*(x(1)-c)];
    x0 = [1 1 0]; % initial condition for Rossler system
    [t,x] = ode45(f,tspan,x0); % call ode() to solve Rossler system
    count = find(t>100); % find all the t values which is >10
    x = x(count,:);
    j = 1;
    n = length(x(:,1)); % find the length of vector x1(x in our problem)
    this_xmax = [];
    for i=2 : n-1
        % check for the min value in 1st column of sol matrix
        if (x(i-1,1)+eps) < x(i,1) && x(i,1) > (x(i+1,1)+eps)
            this_xmax(j) = x(i,1);
            j=j+1;
        end
    end

    % Keep track of what's the maximum number of columns
    maxNumCols = max(maxNumCols, numel(this_xmax));
    % Store this row into the output cell array.
    xmax_cell{k} = this_xmax;
end

% Fix up xmax - push each row into the resulting matrix.
xmax = NaN(numel(crange), maxNumCols);
for idx = 1:numel(crange)
    this_max = xmax_cell{idx};
    xmax(idx, 1:numel(this_max)) = this_max;
end

% Plot
plot(crange, xmax', 'k.', 'MarkerSize', 1)
xlabel('Bifuracation parameter c');
ylabel('x max');
title('Bifurcation diagram for c');

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