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.

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

Answer 1

[Mr.Gh]

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