I keep running into a problem where my code keeps telling me that "Values in t_eval are not properly sorted." I have tried using sort functions and manually sorting (below). What am I not seeing? I’m not sure how to fix this problem. I’m almost certain it’s something very simple that I’m overlooking, but I can’t find it and the assignment is due in an hour.
def pff(t, y, p):
if (2 < t) and (t < 4):
z = 1
else:
z = 0
dy = np.zeros(2)
dy[0]= (p[0] * (y[1] + z)**p[3]) / (1 + (y[1] + z)**p[3]) - (p[2] * y[0])
dy[1]= (p[1] * (y[0] + z)**p[3]) / (1 + (y[0] + z)**p[3]) - (p[2] * y[1])
alpha = 2
beta = 2
gamma = .5
n = 2
k = 1
p = [gamma, k, n, alpha, beta]
x_0 = np.zeros([0,])
t_span = [0, 20]
sol = integrate.solve_ivp(pff, t_span, x_0, 'RK45', p)
Traceback:
ValueError Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_36808/2811005318.py in <module>
9 t_span = [0, 20]
10
---> 11 sol = integrate.solve_ivp(pff, t_span, x_0, 'RK45', p)
~\anaconda3\lib\site-packages\scipy\integrate\_ivp\ivp.py in solve_ivp(fun, t_span, y0, method, t_eval, dense_output, events, vectorized, args, **options)
527 d = np.diff(t_eval)
528 if tf > t0 and np.any(d <= 0) or tf < t0 and np.any(d >= 0):
--> 529 raise ValueError("Values in `t_eval` are not properly sorted.")
530
531 if tf > t0:
ValueError: Values in `t_eval` are not properly sorted.
>Solution :
From the solve_ivp docs
args tuple, optional
Additional arguments to pass to the user-defined functions. If given, the
additional arguments are passed to all user-defined functions. So if, for
example, fun has the signature fun(t, y, a, b, c), then jac (if given) and
any event functions must have the same signature, and args must be a tuple
of length 3.
where as t_eval is the one that’s supposed to be sorted – if provided.
t_eval array_like or None, optional
Times at which to store the computed solution, must be sorted and lie
within t_span. If None (default), use points selected by the solver.