How to find derivative of CSV data plot?

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jasper kansiime
jasper kansiime 2018-9-28
评论： Star Strider 2018-9-30
I have a csv file with uniform points but i would like to write MATLAB code for obtain the derivative of the plotted function(unknown) with time. How can i do this?
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Star Strider
Star Strider 2018-9-28
It is easiest to use the gradient (link) function:
[D,S,R] = xlsread('Uniform_points.csv');
t = D(:,1);
f = D(:,2);
dt = mean(diff(t));
df = gradient(f,dt);
figure
subplot(2,1,1)
plot(t, f)
grid
title(S{2},'Interpreter','none')
xlabel(S{1})
subplot(2,1,2)
plot(t, df)
grid
title(['d(',S{2},')/dt'],'Interpreter','none')
xlabel(S{1})
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jasper kansiime
jasper kansiime 2018-9-30
Thanks for the discussion link.It clarified things alot.I have another question
In the above code you have" plot(t, f)" where "t" represents time axis. How can i scale the current time axis(0-1second) into an X-axis from(0- 0.4seconds) in steps of 0.04 seconds?
Star Strider
Star Strider 2018-9-30
To simply alter the plot x-tick labels, this works:
t_new = 0:0.04:0.4;
figure
plot(t, f)
xt = get(gca, 'XTick');
xtv = linspace(min(xt), max(xt), numel(t_new));
set(gca, 'XTick', xtv, 'XTickLabel',t_new)
I generalised it, so it is a bit more complicated than it needs to be for the current values. It will work for other ‘t_new’ vectors without further modification.

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