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checking of answers ==

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grace lim
grace lim 2022-2-23
编辑： AndresVar 2022-2-23
how to check if Zin==Yin in this case?
thank you in advance

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回答（1 个）

Walter Roberson
Walter Roberson 2022-2-23
You can try
simplify(Zin == Yin)
or
simplify(Zin - Yin)
but you might need to
isAlways(Zin == Yin)
Note: if isAlways tells you that it could not decide, then it still might be equal, but not necessarily.
  2 个评论
grace lim
grace lim 2022-2-23
so in this case, are they equal?when i key in simplify(Zin==Yin)
AndresVar
AndresVar 2022-2-23
编辑：AndresVar 2022-2-23
Ran in:
@grace lim it doesn't seem to be always true
I don't know what are the conditions for your variables but you can see for example if y11,y12,y21,y22 and yL all equal 1 then it is not equal
syms y11 y12 y21 y22 yL
Zin = 1/y11+y12/y11^2/(y11*y22-y12*y21+1/yL);
Yin = y11-y12*y21/(y22+yL);
eq = Zin==Yin % equation to prove
eq = 
simplify(eq) % did not return symtrue
ans = 
%isAlways(eq) % returned false 'unable to prove'
%simplify(Zin-Yin) % did not return 0
% an example when equations is true
eqTest = subs(eq,[y11 y12 y21],[1 0 1])
eqTest = 
simplify(eqTest) % returns symtrue
ans = 
symtrue
%isAlways(eqTest) % returned true
%simplify(lhs(eqTest)-rhs(eqTest)) % returned 0, equation was true
% an example when equation is false
eqTest = subs(eq,[y11 y12 y21 y22 yL],[1 1 1 1 1])
eqTest = 
simplify(eqTest)
ans = 
symfalse

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