Not sure why I am getting this error, I have an idea but am not sure how to fix it

Question

This is for a project that I am working on. I am trying to model an intrusive dike of magma cooling in some host or country rock within the earths crust. I am fairly new to coding. I did my best to convert this code form another coding language to python. I have a basic idea of what is going on. I know that I am trying to index something out of range, but am not sure where and or how to fix it. Any help I could get would be greatly appreciated! Thanks in advance.

import numpy as np
import matplotlib.pyplot as plt

#Physical parameters
L = 100 #Length of modeled domain [m]
Tmagma = 1200 #Temp. magma [°C]
Trock = 300 #Temp. of country rock [°C]
kappa = 1e-6 #Thermal diffusivity of rock [m^2/s]
W = 5 #Width of dike [m]
day = 3600*24 #seconds per day
dt = 1*day #Timestep
print(kappa)
print(day)
print(dt)



#Numerical parameters
nx = 201 #Number of gridpoints in x-direction
nt = 500 #Number of timesteps to compute
dx = L/(nx-1) #Spacing of grid
x = np.linspace(-50,50,100) #Grid
print(dx)
print(x)

#Setup initial temp. profile
T = np.ones(np.shape(x))*Trock
T[x>=-W/2] = 1200
T[x>=W/2] = 300
print(T)


time = 0
for n in range(0,nt): #Timestep loop
    #compute new temp.
    Tnew = np.zeros((1,nx))
    print(Tnew)
    for i in range(2,nx-1):
        Tnew[i] = T[i]+kappa*dt*((T[i+1]-2*T[i]+T[i-1])/(dt**2))             # Set BC's
    Tnew[1] = T[1]
    Tnew[nx] = T[nx]

    #update temp. and time
    T = Tnew
    time = time+dt

    #Plot solution
    plt.figure()
    plt.plot(x,Tnew)
    plt.xlabel('x [m]')
    plt.ylabel('Temerpature [°C]')
    plt.legend()
    surf = ax.plot_surface(X, Y, cmap=cm.coolwarm, linewidth=0, antialiased=False)
    fig.colorbar(surf, shrink=0.5, aspect=5)
    plt.show()

---

IndexError                                Traceback (most recent call last)
<ipython-input-51-e80d6234a5b4> in <module>()
     37     print(Tnew)
     38     for i in range(2,nx-1):
---> 39         Tnew[i] = T[i]+kappa*dt*((T[i+1]-2*T[i]+T[i-1])/(dt**2))
     40 
     41     # Set BC's

IndexError: index 2 is out of bounds for axis 0 with size 

Answer 1

The shape you gave Tnew is (1,nx) , ie it's a 1-by- nx 2D array.

If you only want a 1D array, set Tnew = np.zeros(nx) instead. Or if you want to keep it 2D, access it at Tnew[0,i] .

Answer 2

Tnew = np.zeros((1,nx))

This will gives you one array of nx element inside array (Two dimensional array) and you need to access it like Tnew[0][i]

just change it to

Tnew = np.zeros((nx))

check numpy.zeros DOC

NOTE : After resolving this error you are going to face is Index error at "T[i+1]" which is because when your 'i' reaches at last element you are not going to get 'i+1' element in 'T'.