MATLAB: RandomPoints plot &scatter

MATLABrand

Bonjour,

Je besoin de tracer une figure qui contient 20 points randomisées dans une area [-100 100]. Je veux obtenir cette figure 10^6 càd 10^6 figures, chacune contient 20 points. pourriez vous m'aider,j'essaye d’utiliser la syntaxe rand(n)

merci

set(gca,'xtick',-100:20:100);
set(gca,'ytick',-100:20:100);
axis([-100 100 -100 100]);
grid

Best Answer

How about this:

x = 200 * rand(1,20) - 100;
y = 200 * rand(1,20) - 100;
plot(x, y, 'b*');
grid on;

Related Solutions

MATLAB: RandomPoints &condition distance

Current version, [Last EDITED, 01.02.2017 16:52 UTC]

function [X, Y, D] = GetPointsRandom(nWant, XWidth, YWidth, R)
X       = zeros(nWant, 1);
Y       = zeros(nWant, 1);
dist_2  = R ^ 2;  % Squared once instead of SQRT each time
iLoop   = 1;      % Security break to yoid infinite loop
nValid  = 0;
while nValid < nWant && iLoop < 1e6
  newX = XWidth * (rand - 0.5);
  newY = YWidth * (rand - 0.5);
  if all(((X(1:nValid) - newX).^2 + (Y(1:nValid) - newY).^2) > dist_2)
    % Success: The new point does not touch existing points:
    nValid    = nValid + 1;  % Append this point
    X(nValid) = newX;
    Y(nValid) = newY;
  end
  iLoop = iLoop + 1;
end
% An error is safer than a warning:
if nValid < nWant
  error('Cannot find wanted number of points in %d iterations.', iLoop)
end
% [Edited start] "figure" inserted, 'Parent' used, 'XGrid' inserted:
FigH  = figure;
AxesH = axes('XTick', -100:20:100, 'YTick', -100:20:100, ...
     'XLim', [-100, 100], 'YLim', [-100, 100], ...
     'XGrid', 'on', 'YGrid', 'on', 'NextPlot', 'add', ...
     'Parent', FigH);   
plot(X, Y, 'b*', 'Parent', AxesH);
% [EDITED end]
if nargout > 2
  % D = pdist([X, Y]);   % Faster with statistics toolbox
  D = sqrt(bsxfun(@minus, X, X.') .^ 2 + bsxfun(@minus, Y, Y.') .^ 2);
end
end

Call this e.g. as:

[X, Y, D] = GetPointsRandom(1000, 1e6, 1e6, 6)

The list of coordinates is expanded, when a new random point does not touch any exitsing points.

If you do not have the Statistics Toolbox for pdist, use e.g. http://www.mathworks.com/matlabcentral/fileexchange/15145-distance-matrix.

The suggested method for the distance matrix computes the full matrix, although it is symmetric. For in the number of points is small (< 10000), this is not tragic.

This rejection method works reliably and fast up to a number of about 700 points for a side length of 200 and a diameter of 6. If it fails due to reaching the iteration limit, check if increasing the limit helps. If not, the area is nearly filled up by circles and there will not be a solution for your problem.

MATLAB: Workspace & LOOP FOR

"Avez vous une idée ?"

yes: don't do this. Read this to know why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

No matter how much beginners love to invent the idea of dynamically naming their variables, it is a slow, buggy, and obfuscated way to write code. Learn to write efficient code using indexing. You will not regret doing this.

In your case a 3D matrix might be best (if all output matrices are the same size), something like this (pseudocode):

 P = 50;
 mat = NaN(R,C,P);
 for k = 1:P
     mat(:,:,k) = your calculation here;
 end

Otherwise a cell array will do the job as well.

Best Answer

Related Solutions

MATLAB: RandomPoints &condition distance

MATLAB: Workspace & LOOP FOR

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