Find unknown from the equation with given value

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Sheryl
Sheryl 2013-3-9
回答： prasad p 2021-6-28
I need to calculate the unknown in the equation, how could i do so using matlab?
this is the equation: c=(1/(tm=60))*(tm*exp(-t/tm)-60*exp(-t/60))
value c and t will be provided
how could find the value tm using matlab?

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采纳的回答

Walter Roberson
Walter Roberson 2013-3-10
Using similar ideas to the above:
[...] %define your values for c and t first
syms tm
double( solve( c - ( (1/(tm-60))*(tm*exp(-t/tm)-60*exp(-t/60)) ), tm ) )
or if you have a bunch of these to solve,
syms c t tm
tmfun = matlabFunction( solve( c - ( (1/(tm-60))*(tm*exp(-t/tm)-60*exp(-t/60)) ), tm ), 'vars', {c, t} );
then after that,
tmfun( current_c, current_t )

更多回答（2 个）

Sven
Sven 2013-3-10
Hi Sheryl, If you have the Symbolic Maths toolbox, you can do something like:
Step 1: Set up your equation. Note that you had "tm=60" inside some parentheses. This seems like a typo... I changed it to "tm-60" instead.
myEqn = sym('c = (1/(tm-60))*(tm*exp(-t/tm)-60*exp(-t/60))')
Step 2: Tell MATLAB two of your variables (say, t=5 and c=45):
newEqn = subs(myEqn,{'t','c'}, [5,45])
Step 3: Ask MATLAB to solve for the remaining term (which is tm):
solve(newEqn)
ans =
-0.59449842358712896610400951227259
Is that what you were trying to do?
  2 个评论
Paige
Paige 2013-3-10
编辑：Paige 2013-3-10
Hi, I have tried this and it keeps coming up with the error 'Warning:Explicit solution could not be found', or
1/(lambertw(0, -(703687441776640*exp(-10555311626649600/124074044717989621))/372222134153968863)/5 + 2111062325329920/124074044717989621)
And I have tried to work out what lambertw means with no luck. Why is this?
Thanks in advance

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prasad p
prasad p 2021-6-28
I want to solve above equation in matlab. I want to slove for unknown value of t4 and t2. But I need the solution t2 and t4 for a range of Please help me to write a code for this in matlab software.

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