Matlab Skills

Posted on November 12, 2022July 20, 2023Matlab

Contents

Partialy load and save .mat file

Matlab is RAM-greedy.
Can load/write .mat files partially to mitigate it.
{Matlab-doc}
Quick start

exampleObject = matfile('topography.mat')

varlist = who(exampleObject)

&#91;nrows,ncols] = size(exampleObject,'B');

load('example.mat','B');

save('mycopy_durer.mat','-v7.3')

save('example.mat','-append','B');

exampleObject = matfile('topography.mat')

varlist = who(exampleObject)

[nrows,ncols] = size(exampleObject,'B');

load('example.mat','B');

save('mycopy_durer.mat','-v7.3')

save('example.mat','-append','B');

To load and partially with regular expression:

% laod all vars except for waveforms
load GR_LQ_22may2019 -regexp ^(?!waveforms$).;

% run and save new locsArray
run('./eventRepoMT.m');
save('locsArray.mat', 'locsArray','-v7.3');
disp(size(locsArray))

% laod all vars except for waveforms

load GR_LQ_22may2019 -regexp ^(?!waveforms$).;

% run and save new locsArray

run('./eventRepoMT.m');

save('locsArray.mat', 'locsArray','-v7.3');

disp(size(locsArray))

Note that MatLab has 2 ways to call functions:

load durer.mat X       % command form
load('durer.mat','X')  % function form

1 2	load durer.mat X % command form load('durer.mat','X') % function form

{Ref-Mathwork}

Renew saved figure files

retrieve data from matlab figure file for new plot.
For python user, matlab plot functions are almost the same as matplotlib, except no prefix like plt.* needed.
Ref: https://www.mathworks.com/matlabcentral/answers/100687-how-do-i-extract-data-from-matlab-figures

The interactive notebook (.mlx file) is extremely handy for development. It can convert the block into local function, increase the recallability of the code blocks. Here shows a local function for retrieve the data in figure file and replot them in new layout.

newFig = replot('./gr_lq_justP.fig', 'Pressure (MPa)');

newFig = replot('./load_AE.fig', 'Load (lb)');

function newFig=replot(oldFigPath, ylabels)
    fig = openfig(oldFigPath);
    dataObjs = findobj(fig, '-property', 'XData');
    xData = dataObjs.XData; yData = dataObjs.YData;
    newFig = figure()
    fontsize(newFig, 12, "points");
    set(newFig, 'Units', 'inches', 'Position', &#91;0, 0, 2.5, 2]);
    ln = plot(xData, yData, 'k'); xlabel('Time (s)'); ylabel(ylabels)
end

newFig = replot('./gr_lq_justP.fig', 'Pressure (MPa)');

newFig = replot('./load_AE.fig', 'Load (lb)');

function newFig=replot(oldFigPath, ylabels)

fig = openfig(oldFigPath);

dataObjs = findobj(fig, '-property', 'XData');

xData = dataObjs.XData; yData = dataObjs.YData;

newFig = figure()

fontsize(newFig, 12, "points");

set(newFig, 'Units', 'inches', 'Position', [0, 0, 2.5, 2]);

ln = plot(xData, yData, 'k'); xlabel('Time (s)'); ylabel(ylabels)

end

Basic

data structure

{, } for cell array, analogous to python list
[,] for array
(,) for indices

Variables general info

Use whos, can combine it with -regexp. {Link}

batch run matlab

Introduce a unix command: xargs
It will convert the stdin to stdout.
See detailed Chinese introduction in Here

So option:

-p get permission for each run
-n2 output 2 each batch
-I {} will replace with the output
-P 2 for parallel with 2 threads, but better use with -n1 to pass the task one by one

batch downloading:

cat url.txt | xargs -n2 bash -I 'wget {} -O {}'

1	cat url.txt \| xargs -n2 bash -I 'wget {} -O {}'

where the url.txt is like

https:&#47;&#47;www.xxx.yyy/a1
filename1
https://www.xxx.yyy/a2
filename2
https://www.xxx.yyy/a3
filename3

https://www.xxx.yyy/a1

filename1

https://www.xxx.yyy/a2

filename2

https://www.xxx.yyy/a3

filename3

But now for simplicity, I just input the dropbox link without ?dl=0 in a txt file and run:

cat files.txt | xargs -n1 -P2 wget -q

1	cat files.txt \| xargs -n1 -P2 wget -q

where -q is quiet wget, otherwise wget output will jam the window, -n1 is output one by one and -P2 is parallel with 2 threads

Use matlab in Terminal

The command is

matlab -nodesktop

1	matlab -nodesktop

Only run script and record all output as log


matlab -nodesktop -r 'scripts.m' -logfile 'log.txt'

1 2	matlab -nodesktop -r 'scripts.m' -logfile 'log.txt'

Note: matlab for loop has poor compatibility with global variables. Maybe while loop is better.