如何在Octave中找到函数的导数？
如何在Octave中找到函数的导数？
提问于 2016-03-27 11:39:50
输入：
Xf=和保存点的x值的数组
Yf=保存点方法的y值的数组=2点向前差，2点向后差，3点中心差，5点中心差
输出：
X=包含可实际使用所选方法的有效x值的数组(例如，不能在Xf数组，因为它后面没有值)
DF=这些点处的导数
我需要给一个脚本一组点，然后计算这些点的导数使用4种不同的方法而不使用内置的派生函数，比如diff..。我需要一些帮助来编写其中的一个代码，然后我想我应该能够弄清楚如何完成其余的工作。
2-point forward difference
我的尝试是：
[a, minidx] = min(Xf);
[b, maxidx] = max(Xf);
n = 10;
h = (b-a)/n;
f = (x .^3) .* e.^(-x) .* cos(x);
If method = "forward" #Input by user
X = [min(Xf), Xf(maxidx-1)];
for k = min(Xf):n # not sure if this is the right iteration range...
f(1) = f(x-2*h) + 8*f(x +h);
f(2) = 8*f(x-h) + f(x+2*h);
DF = (f1-f2)/(12*h);
endfor
endifStack Overflow用户
发布于 2016-03-27 22:16:02
以下是有关Matlab如何计算导数的一些文档：
diff Difference and approximate derivative.
diff(X), for a vector X, is [X(2)-X(1) X(3)-X(2) ... X(n)-X(n-1)].
diff(X), for a matrix X, is the matrix of row differences,
[X(2:n,:) - X(1:n-1,:)].
diff(X), for an N-D array X, is the difference along the first
non-singleton dimension of X.
diff(X,N) is the N-th order difference along the first non-singleton
dimension (denote it by DIM). If N >= size(X,DIM), diff takes
successive differences along the next non-singleton dimension.
diff(X,N,DIM) is the Nth difference function along dimension DIM.
If N >= size(X,DIM), diff returns an empty array.
Examples:
h = .001; x = 0:h:pi;
diff(sin(x.^2))/h is an approximation to 2*cos(x.^2).*x
diff((1:10).^2) is 3:2:19
If X = [3 7 5
0 9 2]
then diff(X,1,1) is [-3 2 -3], diff(X,1,2) is [4 -2
9 -7],
diff(X,2,2) is the 2nd order difference along the dimension 2, and
diff(X,3,2) is the empty matrix.下面是另一个示例：
xp= diff(xf);
yp= diff(yf);
% derivative:
dydx=yp./xp;
% also try:
dydx1=gradient(yf)./gradient(xf)页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/36243590
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