Global symbolic variable definition

Question

Kazim 2013-3-1

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https://ww2.mathworks.cn/matlabcentral/answers/65471-global-symbolic-variable-definition

评论： Walter Roberson 2016-12-17

Hi Dear Matlab users

I defined a variable in .M file and assigned a symbolic value to that variable.Then I defined a function and I want to use that variable in this function I wrote.

I tried to define that variable global but program declares it double default and when it tries to assign the symbolic equation to that variable; it can not convert sym to double. How can I solve this problem ?

Thank you

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Azzi Abdelmalek 2013-3-1

How did you know that program declares it double?

Kazim 2013-3-1

编辑：Kazim 2013-3-1

I know it makes the variable double because gives me an error that can not convert sym to double when the program tries to assign the symbolic expression to that variable. For example;

Global a

syms x y

a=x^2*y ----> Here it says can not convert sym to double . I just want my variable a becomes global not double. I want the variable remains symbolic. How could it be achieved ?

Global syms a ----> If I write like that syntax error it says

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Answer 1

Azzi Abdelmalek 2013-3-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/65471-global-symbolic-variable-definition#answer_77021

编辑：Azzi Abdelmalek 2013-3-1

在 MATLAB Online 中打开

In windows command you should declare a as a sym global

syms a
global a

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mohammad m 2016-12-17

编辑：mohammad m 2016-12-17

在 MATLAB Online 中打开

hi in matlab 2013 i use like this but i get error that : undefined variable's. i want to use

    syms x
    global x

in my code, Then in my function in other mfile use this variable without syms in funcyion, like this

    function a=f
     f=x 
    end

but i get error, its not possible or my code is wrong? i don't want to use syms in my function, because it reduce speed.

Walter Roberson 2016-12-17

在 MATLAB Online 中打开

global x   %has to go before the syms
syms x

and then in your function

    function a=f
     global x
     a=x 
    end

If you are trying to avoid the syms call because of the overhead, but want to use the symbol, then you should consider passing it to your function instead of using global. global is the slowest method of accessing variables. You should consider parameterizing your functions to include the symbol that you want to work with.

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