Error in defining symbolic function

Question

Akshay Kumar 2021-6-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/867283-error-in-defining-symbolic-function

回答： Amit Bhowmick 2021-6-29

采纳的回答： Amit Bhowmick

在 MATLAB Online 中打开

Trying to define a symbolic function to calculate its derivative. My attempted code is attached.

I am getting following error " The following error occurred converting from sym to double:

Unable to convert expression containing symbolic variables into double array. Apply 'subs' function

first to substitute values for variables."

Any help will be highly appreciated.

close all; clear; clc;
syms g(a,b)
    g = output(a,b);
function out = output(a,b)
for i = 1:10
   p(i) = i^2+a*b;
   if i==1
       q(i) = 2;
   else
       q(i)= p(i-1);
   end
end 
out = sum(p.*q);
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Amit Bhowmick 2021-6-29

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/867283-error-in-defining-symbolic-function#answer_735613

在 MATLAB Online 中打开

Hope this will work

close all; 
clear; 
clc;
syms a b g(a,b) %Changes
     g = output(a,b);
function out = output(a,b)
for i = 1:10
   p(i) = i^2+a*b;
   if i==1
       q(i) = str2sym(num2str(2));%Changes
   else
       q(i)= p(i-1);
   end
end 
out = sum(p.*q);
end
%output
%g =
%2*a*b + (a*b + 1)*(a*b + 4) + (a*b + 4)*(a*b + 9) + (a*b + 9)*(a*b + 16) + (a*b + 16)*(a*b + 25) + (a*b + 25)*(a*b + 36) + (a*b + 36)*(a*b + 49) + (a*b + 49)*(a*b + 64) + (a*b + 64)*(a*b + 81) + (a*b + 81)*(a*b + 100) + 2;