solve equation for a variable
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I'm sure this sort of thing has been posted numerous times, but I can't find anything that works for me for whatever reason. I need to solve an equation for a variable, and I can't remember how to do this. It's been a while since I've used matlab. I need to solve for t numerically. This is the last thing I tried:
v = 2.42;
si_f235 = 577E-24;
N_235 = 780.63E18;
phi = 3E13;
si_a235 = 101E-24;
si_a238 = 2.73E-24;
N_238 = 21.52E21;
n = 1.5;
eqn = @(x) v*si_f235*N_235(1-si_f235*phi*x)/(si_a235*N_235*(1-si_a235*phi*x)+si_a238*N_238*(1-si_a238*phi*x))==n;
t = vpasolve(eqn , x)
it's just telling me that x is an unrecognized variable
采纳的回答
This works for me (you were also missing an * in your equation):
v = 2.42;
si_f235 = 577E-24;
N_235 = 780.63E18;
phi = 3E13;
si_a235 = 101E-24;
si_a238 = 2.73E-24;
N_238 = 21.52E21;
n = 1.5;
syms x
eqn = v*si_f235*N_235*(1-si_f235*phi*x)/(si_a235*N_235*(1-si_a235*phi*x)+si_a238*N_238*(1-si_a238*phi*x))==n;
t = vpasolve(eqn , x)
3 个评论
SETH SCHREINER
2023-2-28
SETH SCHREINER
2023-2-28
Anton Kogios
2023-2-28
Yes sorry, this requires the Symbolic Math Toolbox, which is very helpful for these sorts of problems. You could of course always follow Torsten's advice in his answer.
更多回答（1 个）
You don't need a toolbox for this.
Take a piece of paper and a pencil, multiply the equation by the denominator of the left-hand side, collect terms with x on one side and other terms on the other side, factor out x on the one side and solve for x.
It's just like solving 3*x + 5 = 7*x - 4 for x.
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