lab-5-implicit-euler-method.py

from math import sin, pi
import matplotlib.pylab

U_max = 100
f = 50
R1 = 5
R2 = 4
R3 = 7
C1 = 0.0003
C2 = 0.00015
final_time = 0.2
step = 0.0000001


def u1(t):
    return U_max * sin(2 * pi * f * t)


differential_equations = [
    lambda X, t:
        (1 / C1) * (1 / (1 + R1 / R2 + R1 / R3)) * (u1(t) * (1 / R2 + 1 / R3) - X[0] * (1 / R2 + 1 / R3) - X[1] / R3),
    lambda X, t:
        (1 / C2) * (1 / R3) * (u1(t) - X[0] - X[1] -
                               (1 / (1 / R1 + 1 / R2 + 1 / R3)) * (u1(t) * (1 / R2 + 1 / R3) -
                                                                   X[0] * (1 / R2 + 1 / R3) - X[1] / R3)),
]


def find_plot():
    current_time = 0
    result = []
    X = [0, 0]
    while current_time < final_time:
        previous = []
        for i in range(len(X)):
            previous.append(X[i] + step * differential_equations[i](X, current_time))
        for i in range(len(X)):
            X[i] += step * differential_equations[i](previous, current_time)
        result.append(X[1])
        current_time += step
    return result


def build_graph(times, result):
    matplotlib.pylab.plot(times, result)
    matplotlib.pylab.ylabel('U2')
    matplotlib.pylab.xlabel('current_time')
    matplotlib.pylab.savefig("graphs/lab5_U2.png")


def main():
    times = [step * i for i in range(int(final_time / step))]
    result = find_plot()
    build_graph(times, result)


if __name__ == '__main__':
    main()