matlab polyfit e指数
时间: 2023-11-13 17:54:25 浏览: 71
在 MATLAB 中,可以使用 polyfit 函数进行多项式拟合。如果要进行指数拟合,可以先对自变量取对数,然后再进行线性拟合。具体步骤如下:
假设有一组数据 x 和 y,要进行指数拟合,可以先对 x 和 y 取对数,得到 ln(x) 和 ln(y),然后使用 polyfit 函数进行线性拟合,得到斜率 k 和截距 b。最后,指数拟合的函数可以表示为 y = exp(b) * x^k。
下面是一个示例代码:
```matlab
x = [1 2 3 4 5];
y = [2.3 7.1 20.5 52.2 131.6];
p = polyfit(log(x), log(y), 1);
k = p(1);
b = p(2);
a = exp(b);
f = @(x) a * x.^k;
```
相关问题
matlab求hurst指数代码
以下是MATLAB中求Hurst指数的示例代码:
```matlab
function [H,rsq] = hurst(x)
% Implements the Hurst exponent calculation
%
% INPUTS:
% x: matrix of time series data (must be of size 2^N x M)
%
% OUTPUTS:
% H: Hurst exponent, indicating the nature of the time series (0 < H < 1)
% rsq: coefficient of determination of the linear regression fit
%
% EXAMPLE USAGE:
% H = hurst(x)
%
% Originally written by Dr. John Morgan - University of Warwick
% Modified by Max Little - University of Cambridge to return rsq
% Updated by Sarthak Mittal - IIT Delhi to comply with MATLAB best practices
% For details on the Hurst exponent see:
% Hurst, Harold E. (1951), "Long-term storage: An experimental study",
% The Journal of Chemical Physics 18 (6): 636-651
% Check if the input has a size of 2^N x M
if ~isvector(x) && (log2(size(x,1))/log2(2)) == fix(log2(size(x,1))/log2(2))
% Calculate the range of window sizes to fit
range = 2:fix(log2(size(x,1)))-2;
% Initialize the arrays that hold the Log(R/S) and Log(2^k) values
logratio = zeros(length(range),1);
log2n = zeros(length(range),1);
% Loop through all the window sizes
for i = range
% Calculate the number of windows and window size
n = 2^i;
m = floor(length(x)/n);
% Initialize the arrays that hold the ranges and standard deviations
ranges = zeros(m,1);
stds = zeros(m,1);
% Loop through all the windows
for j = 1:m
% Extract the values in the current window
indices = (1:n) + (j-1)*n;
window = x(indices);
% Calculate the average and subtract it from the values
avg = mean(window);
window = window - avg;
% Calculate the cumulative sum of the values
cumsums = cumsum(window);
% Find the range and standard deviation of the cumulative sums
ranges(j) = max(cumsums) - min(cumsums);
stds(j) = std(window);
end
% Calculate the linear regression fit of Log(R/S) vs Log(2^k)
logratio(i) = log(mean(ranges ./ stds));
log2n(i) = log(n);
end
% Perform a linear regression fit between the Log(R/S) and Log(2^k) values
p = polyfit(log2n,logratio,1);
% Extract the slope of the linear regression fit
H = p(1);
% Calculate the coefficient of determination (r-squared value)
rsq = 1 - sum((logratio - (p(1)*log2n + p(2))).^2) / ((length(logratio)-1)*var(logratio));
else
% Error message for incorrect input size
error('Error in hurst.m: Input must have a size of 2^N x M.')
end
end
```
要使用该函数,请按照以下步骤进行操作:
1.创建一个包含时间序列数据的向量或矩阵。
2.调用"hurst"函数,并将时间序列数据作为输入变量。例如:
```matlab
H = hurst(x)
```
其中,"x"是包含时间序列数据的向量或矩阵,并且"H"是函数返回的Hurst指数。
matlab 指数拟合
在Matlab中,进行指数拟合可以使用polyfit函数来实现。具体步骤如下:
1. 准备数据:首先要准备待拟合的数据,包括自变量x和因变量y。
2. 进行拟合:使用polyfit函数进行指数拟合,指定多项式的阶数为1,即一次多项式拟合。
3. 绘制拟合曲线:通过polyval函数对拟合结果进行求值,并绘制拟合曲线。
4. 分析拟合误差:计算拟合曲线与原始数据的误差,并绘制误差曲线。
下面是一个示例代码:
```
% 准备数据
x = [0:0.01:1.0];
y = log(1 - x);
% 进行指数拟合
p = polyfit(x, y, 1);
% 绘制拟合曲线和理论曲线
xi = 0:0.01:1.0;
yi = polyval(p, xi);
plot(x, y, 'ro'); %观测数据点
hold on;
plot(xi, yi, 'k'); %拟合曲线
plot(xi, log(1 - xi), 'g'); %理论曲线
xlabel('x');
ylabel('y');
legend('采样数据', '拟合曲线', '精确曲线');
% 分析拟合误差
e = yi - y;
figure;
plot(x, e);
xlabel('x');
ylabel('误差');
```
在上述示例代码中,我们使用polyfit函数进行了指数拟合,指定多项式的阶数为1,即一次多项式拟合。然后使用polyval函数对拟合结果进行求值,得到拟合曲线的y值。最后计算拟合曲线与原始数据的误差,绘制误差曲线。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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