ode return NaN :(
显示 更早的评论
clc;clear;
Gamma = 5/3;
Lambda = (Gamma+1)/2;
syms y(t) x(t)
eqn1 = diff(y,2)*(y-x) == Lambda/2*diff(y)*(diff(x)-diff(y)/Lambda);
a = sqrt(Gamma*(Lambda-1))/Lambda;
dts = (y-x)/(a*diff(y));
Pp = 1/0.08*(t-dts);
pip = Pp/(1/Lambda);
eqn2 = diff(x,2)*y == (pip-diff(y)^2/Lambda);
eqn = [eqn1 eqn2];
[V,S] = odeToVectorField(eqn);
M = matlabFunction(V,'vars',{'t','Y'});
interval = [0 2];
yInit = [0 0 0 0];
ySol = ode45(M,interval,yInit);
tValues = linspace(0,2,10);
xValues = deval(ySol,tValues,1);
zValues = deval(ySol,tValues,3);
xValues =
0 NaN NaN NaN NaN NaN NaN NaN NaN NaN
In fact, I want to calculate this equation.
采纳的回答
Hi @ZH CC
The odeToVectorField(eqn) returns this
V =
Y[2]
-(9*Y[4]^3 - 160*5^(1/2)*Y[1] + 160*5^(1/2)*Y[3] - 200*t*Y[4])/(12*Y[3]*Y[4])
Y[4]
-((4*Y[2] - 3*Y[4])*Y[4])/(6*(Y[1] - Y[3]))
S =
x
Dx
y
Dy
and you can clearly see the divisions by 
and 
. Since the initial values are 
, 
and 
, naturally, the ode45 solver returns NaN.
and . Since the initial values are , and , naturally, the ode45 solver returns NaN.Hope you are satisfied with this Answer.
更多回答（1 个）
Steven Lord
2022-4-20
1 个投票
What is 
at time t = 0? By your formula 14 it is 
times other stuff. Let's ignore that other stuff and look at the value of that term. Well, all of Z(0), X(0), and 
(0) are 0 by your formula 17. So that term is 
which MATLAB correctly computes as NaN.
at time t = 0? By your formula 14 it is times other stuff. Let's ignore that other stuff and look at the value of that term. Well, all of Z(0), X(0), and (0) are 0 by your formula 17. So that term is which MATLAB correctly computes as NaN.My guess is that at least one of Z(0), X(0), and 
(0) must not be 0. In particular, because Z-X appears in the denominator I think one or both of those must be non-zero (and not equal to each other) for your equations to make sense.
(0) must not be 0. In particular, because Z-X appears in the denominator I think one or both of those must be non-zero (and not equal to each other) for your equations to make sense.类别
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