How do rewrite a variable with the symbolic toolbox?

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TG
TG 2019-6-4
评论： madhan ravi 2019-6-4
Hi,
I have a question about the symbolic toolbox. When I use simple relations, I cannot rewrite a variable in another variable. here is an example:
syms a b
a=b+3
solve(a,b)
This leads however to -3, which means that solve assumes that a is 0? I would like an output like b=a-3. If I do this in another way using solve, solve cannot find a solution:
syms a b
a==b+3
solve(a,b)
Does anyone have an idea how I can find b=a-3? It isn't necessary to use solve, but I couldn't think of another way. Thanks in advance!

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采纳的回答

madhan ravi
madhan ravi 2019-6-4
syms a b
eq=a==b+3
isolate(eq,b)
%or
b=solve(eq,b)

更多回答（1 个）

TG
TG 2019-6-4
Do you maybe also know how I can fix this problem?
syms a b c
eq1= a==b+3;
eq2= c==2*b-3;
solve(eq2,eq1,a) % This doesn't work, gives an empty matrix
I would like to get an expression of c == 2*(a-3)-3, so I could then solve a in terms of c for example.

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