A question related to subs in ode (symbolic maths toolbox)

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Angus Wong 2019-7-3

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评论： Angus Wong 2019-7-3

采纳的回答： madhan ravi

I have a line:

ode=diff(y,x)==x+y;

I want matlab to calculate diff(a,b), given a and b are real numerical values. However, the subs function allowed me only to either sub the value a or value b into the ode line, can anyone help?

I am expecting something like subs(ode,[x,1,y,2]) would give me 3, subs(ode,[x,4,y,5]) would give me 9.

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madhan ravi 2019-7-3

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在 MATLAB Online 中打开

I am not sure what you are asking for perhaps an example below?:

>> syms x y
>> eqn = x+2*y
 
eqn =
 
x + 2*y
 
>> subs(eqn,{x,y},{2,5})
 
ans =
 
12
 
>>

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madhan ravi 2019-7-3

在 MATLAB Online 中打开

Perhaps ?:

>> syms y(x)
>> ode=diff(y,x)==x+y;
>> subs(rhs(ode)-lhs(ode),{x,y},{1,2})
ans(x) = 
3
>> subs(rhs(ode)-lhs(ode),{x,y},{4,5}) 
ans(x) = 
9
>> 

Angus Wong 2019-7-3

Thanks a lot! You do make my day.

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