Find unknown from the equation with given value

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?

[Walter Roberson]

http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

Answer 1

[Walter Roberson]

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 )

Answer 2

[Sven]

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?

[Paige]

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

[Walter Roberson]

lambertw is a solution; see http://www.mathworks.com/help/symbolic/lambertw.html and http://en.wikipedia.org/wiki/Lambert_W_function

Answer 3

[prasad p]

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.