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problem with tbl,xvar,yvar form of plot()

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Maciej
Maciej 2024-6-3
编辑： Voss 2024-6-3
Greetings, as per title i have a problem with tbl,xvar,yvar form of plot().
I have an array with history of the evolution of the parameters of a function during parameter optimization.
num_iterations = size(param_history, 1);
num_chains = size(param_history, 2);
num_dimensions = size(param_history, 3);
param_at_step = zeros(num_iterations, num_chains * num_dimensions);
The array is of the form 10000x8 - 10k iterations by 2 parameters for each of the 4 independent optimization chains. I expected:
for iteration = 1 : num_iterations
for chain_id = 1 : num_chains
for param = 1 : num_dimensions
column = ((chain_id-1) * 2) + param;
param_at_step(iteration, column) = param_history(iteration, chain_id, param);
end
end
end
plot( param_at_step, [1 3 5 7], [2 4 6 8] );
to plot the evolution of the parameters in the parameter space, but i get an error:
Error using plot
Specify the coordinates as vectors or matrices of the same size, or as a vector and a matrix that share the same length in at least one dimension.
I am confused, what am I doing wrong?
  1 个评论
Voss
Voss 2024-6-3
Ran in:
The code involving three nested for loops for constructing param_at_step from param_history
param_history = randn(10000,4,2); % random data
num_iterations = size(param_history, 1);
num_chains = size(param_history, 2);
num_dimensions = size(param_history, 3);
param_at_step = zeros(num_iterations, num_chains * num_dimensions);
for iteration = 1 : num_iterations
for chain_id = 1 : num_chains
for param = 1 : num_dimensions
column = ((chain_id-1) * 2) + param;
param_at_step(iteration, column) = param_history(iteration, chain_id, param);
end
end
end
can be more succinctly written using reshape and permute:
num_iterations = size(param_history, 1);
param_at_step_test = reshape(permute(param_history,[1 3 2]),num_iterations,[]);
And the result is the same:
isequal(param_at_step_test,param_at_step)
ans = logical
1

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采纳的回答

Voss
Voss 2024-6-3
what am I doing wrong?
param_at_step is a numeric matrix, not a table, so you are not using the tbl,xvar,yvar form of plot().
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显示 1更早的评论
Maciej
Maciej 2024-6-3
I'll accept this, it answers the question just as it is written.
I have a follow up-however. What if the number of chains and the number of dimensions (aka parameters) are variables that can be configured at the start of the run (lets limit ourselves to 3 dimensions max)?
For e.g. what if i have 6 chains operating in 3 dimensional space?
I could use simple if-elseif-end to switch between plot and plot3 but not sure how to generate those (:,[numbers]) expressions programmaticaly : O
Voss
Voss 2024-6-3
编辑：Voss 2024-6-3
Ran in:
In my opinion, it's easier to plot from the 3D array param_history rather than rearranging it into the matrix param_at_step first.
param_history = randn(10000,6,3); % random data
[num_iterations,num_chains,num_dimensions] = size(param_history);
Here's one simple way:
figure
if num_dimensions > 2
plot3(param_history(:,:,1),param_history(:,:,2),param_history(:,:,3))
else
plot(param_history(:,:,1),param_history(:,:,2))
end
Here's another way:
if num_dimensions > 2
plot_func = @plot3;
else
plot_func = @plot;
end
plot_args = permute(num2cell(param_history,1),[3 2 1]);
figure
plot_func(plot_args{:})
If you need to use param_at_step for whatever reason, then here's how you can do it, generating the vectors of column numbers programmatically:
param_at_step = reshape(permute(param_history,[1 3 2]),num_iterations,[]);
figure
if num_dimensions > 2
plot3(param_at_step(:,1:num_dimensions:end),param_at_step(:,2:num_dimensions:end),param_at_step(:,3:num_dimensions:end))
else
plot(param_at_step(:,1:num_dimensions:end),param_at_step(:,2:num_dimensions:end))
end

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