How to plot the derivative from experimental data
조회 수: 629 (최근 30일)
이전 댓글 표시
Hi I have a number of points (experimental data) plotted as an x-y plot. I want to generate the derivative of y w.r.t x from this plot. Is there a function in MATLAB which can do this ?
TIA
댓글 수: 0
채택된 답변
Star Strider
2014년 5월 19일
편집: Star Strider
2019년 3월 25일
Not a specific MATLAB function, but it’s easy:
dydx = diff(y(:))./diff(x(:));
If you want dydx to be the same length as x and y (so you can plot it against x), ‘zero-pad’ the first value with eps:
dydx = diff([eps; y(:)])./diff([eps; x(:)]);
Both produce a column vector, so you may have to transpose it if x is a row vector in order to plot it with the others.
UPDATE — (24 Mar 2019 00:30)
A much more accurate approach would be:
dydx = gradient(y(:)) ./ gradient(x(:));
댓글 수: 5
Star Strider
2022년 1월 1일
Assuming vector arguments, the diff function takes the differences between successive elements of the vector, so the outputt is one element shorter than the arguments. The gradient function uses a central difference approximation of the derivative (except at the ends, where it calculates a simple difference) so the output has the same number of elements as the argument.
See the documentation on both for details.
.
Shiva Vikram Bhagavatula
2023년 9월 15일
The function sampling may be poor at some or all points if completely different results are obtained for diff and gradient. For example,let the derivative be calculated at point 2 in a set of three points (p1,p2,p3). Assuming the spacing along the independent variable axis is dx, diff produces (p2-p1)/dx . Gradient produces (p3-p1)/(2dx). For them to be equal, the condition is (p3+p1)/2=p2,i.e; all three points are collinear( lie on the same straight line). The difference between gradient and diff would be a measure of the deviation of the points from the collinear fit.
추가 답변 (1개)
Abhinendra Singh
2017년 11월 27일
Hello, Can any one of you please post a working example of the above problem?
I appreciate the help!
댓글 수: 3
John D'Errico
2022년 1월 1일
Um, only one call to gradient needed.
x = 0:0.1:10;
y = sin(x);
plot(x, gradient(y,x));
When gradient is called with TWO arguments, it assumes you have passed in x also as the second argument. Now it computes a derivative estimate at each point. A simple finite difference scheme is used.
help gradient
참고 항목
카테고리
Help Center 및 File Exchange에서 Descriptive Statistics에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!