checking of answers ==

how to check if Zin==Yin in this case?

thank you in advance

Answer 1

[Walter Roberson]

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.

[grace lim]

so in this case, are they equal?when i key in simplify(Zin==Yin)

[AndresVar]

@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