df=-0.013y1-1000y1y2-2500y2*y3

return df

def RK4(x, y1, y2,y3, h):

“”"

:param x: Initial value of X

:param y1: Initial value of y1

:param y2: Initial value of y2

:param y3: Initial value of y3

:param h: time step

:return: New iterative solution

“”"

xarray, y1array, y2array,y3array = [], [], [], []

while x <= 0.02:

xarray.append(x)

y1array.append(y1)

y2array.append(y2)

y3array.append(y3)

x += h

K_1 = f1(x, y1, y2,y3)

L_1 = f2(x, y1, y2,y3)

M_1 = f3(x, y1, y2,y3)

K_2 = f1(x + h / 2, y1 + h / 2 * K_1, y2 + h / 2 * L_1 , y3 + h/2 * M_1)

L_2 = f2(x + h / 2, y1 + h / 2 * K_1, y2 + h / 2 * L_1 , y3 + h/2 * M_1)

M_2 = f3(x + h / 2, y1 + h / 2 * K_1, y2 + h / 2 * L_1, y3 + h / 2 * M_1)