Subs with 2 numbers returns a number

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fdadasd asdasd
fdadasd asdasd 2021-11-10
回答： John D'Errico 2021-11-11
Subs when given 2 numbers, returns a number. But I need a string/function to be returned
example:
>> syms x y;
>> f=-y+x+2;
>> subs(f, [x,y], [2,2])
ans =
2
>>
But I need it: -2+2+2

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回答（2 个）

Star Strider
Star Strider 2021-11-10
Ran in:
It is doing the substitution and the calculation at the same time, and providing the answer.
Using symbolic arguments instead —
syms x y a b
f=-y+x+2;
subs(f, [x,y], [a,b])
ans = 
as expected.
.
John D'Errico
John D'Errico 2021-11-11
Simple enough. Convert the original expression to a string. Now just do string processing, with finds and replace operations.
Can you do it using symbolic computations? Probably not, since subs will combine those numeric constants for you automatically.

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