CODEWITHSUNDEEP
pythonrunge-kutta
Jerry Durkan
Jerry Durkan

Reputation: 13

Using RK4 to solve integrals

The question asks us to solve this integral in python using an Rk4 method ∫sinh(𝑥)(𝑥−5)𝑑𝑥 from 0 to 5. Whats the best way to do this, how would you change this to an ODE?

def RK4(f, dx, x0, y0, imax):
    output = np.empty((imax, 3))
    i = 0
    xi = x0
    yi = y0
    while(i < imax):
        k1 = dx*f(xi,yi)
        k2 = dx*f(xi + 0.5*dx, yi + 0.5*k1)
        k3 = dx*f(xi + 0.5*dx, yi + 0.5*k2)
        k4 = dx*f(xi + dx, yi + k3)

        yi = yi + 1/6*(k1 + 2*k2 + 2*k3 + k4)
        xi += dx
        output[i, 0] = xi
        output[i, 1] = yi[0]
        output[i, 2] = yi[1]
        i += 1
    return output

RK4(0,0,5,100,10)

I get a error that for k1 ("int object is not callable")?? how can I fix this or maybe the issue is somewhere else in my code. Thanks for any help. Also the question explicitly asks us to solve the integral using both Simpsons rule and RK4 methods

Upvotes: 0

Views: 336

Answers (1)

Lutz Lehmann
Lutz Lehmann

Reputation: 26040

You are passing an integer 0 in place of the function. Then in the k1 line you try to use that integer as function, which gives the reported error, as there is no sensible interpretation of 0(0,5). You could use

RK4(lambda x,y:0,0,5,100,10)

However, with a step size of zero no integration will occur.

Upvotes: 1

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