Help with solve please

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Jonathan Quiroz
Jonathan Quiroz 2016-12-7
评论： Walter Roberson 2016-12-14
Hello i have a problem, i have this variables
d = 0.8, E = 157.0627, k= 8.8160e-7, M=1500, s=0.0025, v=2, w= 20, x = 0
and i have this implicit equation
C = (M./(w.*d.*sqrt(4.*pi.*E.*t))).*exp((((x-v.*t).^2)./(-4.*E.*t))-k.*t)
I want to calculate "t" when C=0.018, i was trying with solve but i can´t Could you help me?

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回答（2 个）

Mischa Kim
Mischa Kim 2016-12-7
Jonathan, use fsolve instead.
Walter Roberson
Walter Roberson 2016-12-7
d = 0.8, E = 157.0627, k= 8.8160e-7, M=1500, s=0.0025, v=2, w= 20, x = 0;
syms t
C = (M./(w.*d.*sqrt(4.*pi.*E.*t))).*exp((((x-v.*t).^2)./(-4.*E.*t))-k.*t);
t_sol = solve(C == 0.018, t);
That will give you the solution (6524129310423984846758976886046457856*lambertw(0, 20285218037440766998525581099461327880859375/115890541665100062514421889459201930952704))/83088253081357381625960780183393599 . You might want to double(t_sol) if you were thinking you wanted a numeric solution.
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Jonathan Quiroz
Jonathan Quiroz 2016-12-14
Excuse me how do you make a script with that?
Walter Roberson
Walter Roberson 2016-12-14
d = 0.8, E = 157.0627, k= 8.8160e-7, M=1500, s=0.0025, v=2, w= 20, x = 0;
syms t
C = (M./(w.*d.*sqrt(4.*pi.*E.*t))).*exp((((x-v.*t).^2)./(-4.*E.*t))-k.*t);
t_sol = vpa(C == 0.018, t);
t_num = double(t_sol);

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