Taylor Series on numbers

Question

mathango 2016-1-27

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评论： mathango 2016-1-27

采纳的回答： John D'Errico

在 MATLAB Online 中打开

Hi,

I know that I can perform series expansion of the function let say sin(x) by writing a following script commands:

syms x a
F = a*sin(x)
taylor(F,x,6);

The output is a nice series expansion of sin(x) up to 5th term. However, when I have a number such as F=1 , the taylor gives the error message and fails to give a correct answer which is 1. Is there a way to work around it? Is there a way to verify if F contains variable x or not so that taylor can be avoided when F does not have x variable. Thanks.

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Answer 1

John D'Errico 2016-1-27

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https://ww2.mathworks.cn/matlabcentral/answers/265351-taylor-series-on-numbers#answer_207557

编辑：John D'Errico 2016-1-27

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Works fine for me.

syms x
F = sym(1);
taylor(F,x,5)
ans =
1

What you misunderstand is that taylor does not apply to a double variable. However, it works fine for a symbolic constant.

As for how to tell the difference, here is a thought:

isnumeric(F)
ans =
     0
G = 1;
isnumeric(G)
ans =
     1

Alternatively, you could use a try/catch construct to detect if there was a problem.

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mathango 2016-1-27

Hi John,

Thanks for the answer. The second string of code (isnumeric) works. However, the first string of code with sym(1) method does not work. I think it is due to the fact that I am using old version matlab 6.5 Looks like I have to use the second method and try/catch to get around that limitation. Again, thanks.

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