Why the results are different when use different letters?
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I solve same equations in different ketters and got fifferent results as follow:
But rs=a, xs=b, rp=c and xp=d. the equations are same!
>> syms rs xs rp xp;
>> [rp,xp]=solve(rs*rp^2+rs*xp^2==xp^2*rp,xs*rp^2+xs*xp^2==rp^2*xp)
rp =
-(rp*(rs*(rp - rs))^(1/2))/(rp - rs)
(rp*(rs*(rp - rs))^(1/2))/(rp - rs)
xp =
-(rs*(rp - rs))^(1/2)
(rs*(rp - rs))^(1/2)
-------------------------------------------------------------
>> syms a b c d
>> [c,d]=solve(a*c^2+a*d^2==c^2*d,b*c^2+b*d^2==d^2*c)
c =
0
(a^2 + b^2)/b
d =
0
(a^2 + b^2)/a
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채택된 답변
Walter Roberson
2022년 3월 12일
You are not specifying which two variables to solve for, so solve() is using symvar() and picking the first two variables.
With the different names involved, the relative order of the variables in symvar() is different than you are expecting.
댓글 수: 3
Walter Roberson
2022년 3월 12일
syms rs xs rp xp
[rp,xp]=solve(rs*rp^2+rs*xp^2==rp^2*xp, xs*rp^2+xs*xp^2==xp^2*rp, [rp, xp])
추가 답변 (2개)
DGM
2022년 3월 11일
They are not the same.
syms rs xs rp xp;
[rp,xp] = solve( rs*rp^2+rs*xp^2 == xp^2*rp, xs*rp^2+xs*xp^2 == rp^2*xp)
syms a b c d
[c,d] = solve( a*c^2+a*d^2 == c^2*d, b*c^2+b*d^2 == d^2*c)
The RHS of both equations don't correspond. You'll have to decide which one is which.
Jan
2022년 3월 11일
편집: Jan
2022년 3월 11일
Because the equations are different:
syms rs xs rp xp
syms a b c d
[rp, xp] = solve(rs * rp^2 + rs * xp^2 == xp^2 * rp, xs * rp^2 + xs * xp^2 == rp^2 * xp)
[c, d] = solve(a * c^2 + a * d^2 == c^2 * d, b * c^2 + b * d^2 == d^2 * c)
% ^ ?! ^
You see, the replacement is not performed exactly. The term xp is converted twice to c instead of d.
댓글 수: 6
Jan
2022년 3월 13일
It is an important point to see, that the equations are not equal and that spaces around operators do matter.
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