symbolic substitution symbol by symbol

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kevin k
kevin k on 15 Oct 2015
Edited: Walter Roberson on 15 Oct 2015
Hi
I was trying to replace symbol by symbol with the code:
syms u v x y
N=u+3*v;
u=2*x;
v=2*y;
N=subs(N,[u,v],[2*x,2*y]);
The result I got :
N =
u + 3*v
where is my mistake?

Answers (1)

Martin Schätz
Martin Schätz on 15 Oct 2015
You should not define the u=2*x; v=2*y; because then you get right anwer from subs. It wil simplify the answer and it will be true. Try to run this:
clear all, close all, clc
syms u v x y
N=u+3*v;
N=subs(N,[u v],[2*x 2*y])
and then this:
clear all, close all, clc
syms u v x y
u=2*x; v=2*y;
N=u+3*v
You will get right answer both times.

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