how can I plot y = e^(-2x)Sin2x and its derivative on the same graph using two different colors?

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bachir 2015-9-9

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https://ww2.mathworks.cn/matlabcentral/answers/241775-how-can-i-plot-y-e-2x-sin2x-and-its-derivative-on-the-same-graph-using-two-different-colors

回答： Gilang Setyawan Y.P. 2022-3-7

I'm learning Matlab for the first time and I was able to get the first graph working but i'm having trouble getting the graph of the derivative to work. I keep getting an error message that "vectors must be the same lengths" and that i have an error in line 9.

x = (0:0.02:5);
y= exp(-2*x).*sin(2*x);
subplot(1,2,1)
plot(x,y),xlabel('x'),ylabel('y'), axis([0 5 -1 1])
hold on
diff(y) %differentiation
f = diff(y);
plot(x,f,'r'),xlabel('x'),ylabel('f'), axis([0 5 -1 1]) <-------line 9

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Answer 1

Star Strider 2015-9-9

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The easiest solution is to use the gradient function rather than diff. The gradient function produces a more accurate estimate and the output is the same length as the input, while the output of diff is one element shorter, owing to the different ways the two are calculated.

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bachir 2015-9-9

If v is a scalar, gradient(f,v) = diff(f,v). If v is an empty symbolic object, such as sym([]), then gradient returns an empty symbolic object.

Star Strider 2015-9-10

My pleasure.

The Symbolic Math Toolbox gradient function and the core MATLAB gradient function do somewhat different things. I was intending that you use the core MATLAB gradient function to calculate the numerical derivative of the vector y, essentially the equivalent of the Symbolic Math Toolbox diff function.

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