unexpected string scalar error?

Question

Raphael Hatami 2019-9-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/480134-unexpected-string-scalar-error

编辑： Adam Danz 2019-9-23

Hello, I am trying to do taylor series expansion from 0 order to 3 with base point 1 (and estimating f(3)) for the given equation. However, it is giving me an error: 'Expected a string scalar or character vector for the parameter name.' for the line y =...

I believe the problem has something to do with the '1' in the taylor function. But I don't know how else to define the base point.

Can anybody see what I'm doing wrong? Thank you

f = @(x) 25*x.^3-6*x.^2+7*x-88;
sample_at = 3;
trueval = f(sample_at);
syms xx;
fs = f(xx);
for n = 0:4
  y = double(subs(taylor(f,xx,n,1), xx, sample_at ));
  disp([n, y]);
  %now calculate the relative error
end

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Answer 1

Adam Danz 2019-9-12

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https://ww2.mathworks.cn/matlabcentral/answers/480134-unexpected-string-scalar-error#answer_391600

编辑：Adam Danz 2019-9-23

There are 2 required inputs and 1 optional input to taylor() followed by optional name-value pair arguments. Your call to taylor() contains 4 inputs so matlab is interpreting the extra input(s) as name-value pairs. The name-value pair identifies the parameter with a string scalar or char vector which is why you're getting that error, "Expected a string scalar or character vector for the parameter name.".

Read about this function's inputs and optional name-value pairs here:

https://www.mathworks.com/help/symbolic/sym.taylor.html