Passing arguments to fsolve

Question

I'm solving a nonlinear equation with many constants.
I created a function for solving like:

def terminalV(Vt, data):
    from numpy import sqrt
    ro_p, ro, D_p, mi, g = (i for i in data)
    y = sqrt((4*g*(ro_p - ro)*D_p)/(3*C_d(Re(data, Vt))*ro)) - Vt
    return y

Then I want to do:

data = (1800, 994.6, 0.208e-3, 8.931e-4, 9.80665)
Vt0 = 1
Vt = fsolve(terminalV, Vt0, args=data)

But fsolve is unpacking data and passing too many arguments to terminalV function, so I get:

TypeError: terminalV() takes exactly 2 arguments (6 given)

So, my question can I somehow pass a tuple to the function called by fsolve()?

Solution

The problem is that you need to use an asterisk to tell your function to repack the tuple. The standard way to pass arguments as a tuple is the following:

from numpy import sqrt   # leave this outside the function
from scipy.optimize import fsolve

#  here it is     V
def terminalV(Vt, *data):
    ro_p, ro, D_p, mi, g = data   # automatic unpacking, no need for the 'i for i'
    return sqrt((4*g*(ro_p - ro)*D_p)/(3*C_d(Re(data, Vt))*ro)) - Vt

data = (1800, 994.6, 0.208e-3, 8.931e-4, 9.80665)
Vt0 = 1
Vt = fsolve(terminalV, Vt0, args=data)

Without fsolve, i.e., if you just want to call terminalV on its own, for example if you want to see its value at Vt0, then you must unpack data with a star:

data = (1800, 994.6, 0.208e-3, 8.931e-4, 9.80665)
Vt0 = 1
terminalV(Vt0, *data)

Or pass the values individually:

terminalV(Vt0, 1800, 994.6, 0.208e-3, 8.931e-4, 9.80665)