如何使用fittype函数定义自定义方程式? [英] How can i use fittype function to define a custom equation?

问题描述

如何使用fittype函数定义以下自定义方程式?

How can I use fittype function to define the following custom equation?

y = a(x1^b)(x2^c)(x3^d)(x4^e)(x5^f)(x6^g).

我尝试了以下代码:

ft = fittype( 'a*(x1^b)*(x2^c)*(x3^d)*(x4^e)*(x5^f)*(x6^g)',...
'independent',{'x1','x2','x3','x4','x5','x6'},...
'dependent',{'y'},...
'coefficients',{'a','b','c','d','e','f','g'});

但是会引发此错误:

表达式a *(x1 ^ b)(x2 ^ c)(x3 ^ d)(x4 ^ e)(x5 ^ f)*(x6 ^ g )不是有效的MATLAB表达式，具有非标量系数，或者无法求值:FITTYPE函数的输入不足.

Expression a*(x1^b)(x2^c)(x3^d)(x4^e)(x5^f)*(x6^g) is not a valid MATLAB expression, has non-scalar coefficients, or cannot be evaluated: Not enough inputs to FITTYPE function.

推荐答案

首先，'a *(x1 ^ b)(x2 ^ c)(x3 ^ d)(x4 ^ e)(x5 ^ f)(x6 ^ g)'不是有效的MATLAB表达式.您应该将其更改为'a (x1.^ b).(x2.^ c).(x3.^ d).(x4.^ e).(x5.^f).*(x6.^g)'. 其次，Matlab无法处理这么多未知的参数，一个简短的参数就可以了，像这样:

Firstly, 'a*(x1^b)(x2^c)(x3^d)(x4^e)(x5^f)(x6^g)' is not a valid MATLAB expression. You should change it to 'a(x1.^b).(x2.^c).(x3.^d).(x4.^e).(x5.^f).*(x6.^g)'. Secondly, Matlab cannot process so many unknown parameters, a short one is OK, like this:

ft = fittype(@(a，b，c，x1，x2)a *(x1.^ b).*(x2.^ c)， '独立'，{'x1'，'x2'}，'依赖'，{'y'}，'问题'，{'b'，'c'}));

ft = fittype(@(a,b,c,x1,x2) a*(x1.^b).*(x2.^c), 'independent',{'x1','x2'},'dependent',{'y'},'problem',{'b','c'});

这篇关于如何使用fittype函数定义自定义方程式?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！