DOUBLE cannot convert the input expression into a double array?

Question

Abdullah Türk 2019-10-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/484263-double-cannot-convert-the-input-expression-into-a-double-array

回答： Stephan 2019-10-10

采纳的回答： Stephan

Hi everybody,

I want to calculate a problem about Taylor series from a book but an error message occurred as follows:

Thank you from now.

The following error occurred converting from sym to double:
Error using symengine (line 59)
DOUBLE cannot convert the input expression into a double array.
If the input expression contains a symbolic variable, use VPA.
Error in example_four3 (line 35)
    sol(i+1) = sol(i+1) + (diff(f,(i+1))) * (h^(i+1)/factorial(i+1));

Here is my code:

clc;
clear;
anglout = radtodeg(pi);
true_value = cos(pi/3);
h = pi/3-pi/4;
n = 6; 
syms x
f = cos(x);
sol(1) = cos(pi/4);
for i = 0:n
    sol(i+1) = sol(i+1) + (diff(f,(i+1))) * (h^(i+1)/factorial(i+1));
    sol(1) = sol(i);
end

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Answer 1

Stephan 2019-10-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/484263-double-cannot-convert-the-input-expression-into-a-double-array#answer_395692

clc;
clear;
anglout = rad2deg(pi);
true_value = cos(pi/3);
h = pi/3-pi/4;
n = 6; 
syms f(x) op(x)
f(x) = cos(x);
sol = zeros(1,7);
sol = cos(pi/4);
for i = 0:n
    op(x) = (diff(f,x,(i+1)));
    sol = double(sol + op(i+1) * (h^(i+1)/factorial(i+1)));
end