Hi Everyone,I have a problem with subs command.Because when i tried to input it,it said Undefined variable "subs" or class subs".The Sigma V is supposed to be like this : SigmaV=p+q+V=0 , but mine : SigmaV='p+q+V=0' .The ' is not gone.

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Richard Wijaya
Richard Wijaya 2020-8-30
回答： Mr.Gh 2020-9-3
syms x1 x2 L p q V
>> L=10;p=6;q=2;x1=2.5;x2=7.5;L=10;
>> SigmaV='p+q+V=0'
SigmaV =
'p+q+V=0'
>> SigmaV=subs{SigmaV,{'p,q'},{p,q}}
Undefined variable "subs" or class "subs".
The Command that i copied is from 2010a Mathlab.But i use 2019a Mathlab

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回答（1 个）

Mr.Gh
Mr.Gh 2020-9-3
Hello,
You defined some variables as symbols. Then you change the type of the defined symbolic variables to "double"."subs" command is used to substitute variables into a symbolic expression. but, there is no symbolic expression!!
Check the documentation of the "subs" command.
https://www.mathworks.com/help/symbolic/subs.html

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