problem with symbolic calculation

Question

YOGESHWARI PATEL 2021-3-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/772578-problem-with-symbolic-calculation

评论： YOGESHWARI PATEL 2021-3-17

I want symbolic calculation .I write the code but error is displayed

syms a 
syms R
n=input('enter the value of n')
F(1)=1;
F(2)=0;
F(3)= a;
aplha=input('enter the value of a=')
R=input('enter the value of reynold number R=')
 for i=1:n
  F(i+3)=2*alpha*R*F(i)+F(i+1);   
 end

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Answer 1

Walter Roberson 2021-3-16

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编辑：Walter Roberson 2021-3-16

在 MATLAB Online 中打开

aplha=input('enter the value of a=')

You assign to aplha . A. P. L. H. A

R=input('enter the value of reynold number R=')
 for i=1:n
  F(i+3)=2*alpha*R*F(i)+F(i+1); 

You use alpha . A. L. P. H. A.

You have not assigned to alpha.

alpha happens to exist as a function, but the function alpha requires that you pass a parameter to it, so you would get an error.

You need to change your input() to assign to alpha instead of aplha

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YOGESHWARI PATEL 2021-3-17

Thank you

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Answer 2

Steven Lord 2021-3-14

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The way you've written it, when you try to assign a into F(3) MATLAB needs to convert the symbolic a into a numeric value so it can be stored in the numeric array F. But what is the numeric value of a? It doesn't have one, which is why MATLAB complains.

Since you want F to be able to store symbolic variables, don't initialize it to be a numeric array first. Initialize it as symbolic from the start by assigning a symbolic expression to it to create the array.

F(1) = sym(1);

Or since you know how large it will need to be in the end:

F = sym(zeros(1, n+3));