MethodError: no method matching getindex(::Float64, ::Colon, ::Int64)

Specific Domains Data
1

I am getting error when runing code :point_down:

function alfven_surface(N_r, N_theta, theta, v_r, v_theta, B_r, B_theta, rho, tracer)
    """
    Given poloidal velocity field (vp) and poloidal magnetic field (bp), the function
    calculates the Alfven surface. It is the surface for which vp = bp/sqrt{4*pi*rho}
    """
    v_x = zeros(N_r, N_theta)
    v_z = zeros(N_r, N_theta)

	for i in 1:N_theta
        v_x[:, i] .= v_r[:, i] .* sin(theta[i]) .+ v_theta[:, i] .* cos(theta[i])
        v_z[:, i] .= v_r[:, i] .* cos(theta[i]) .- v_theta[:, i] .* sin(theta[i])
    end

    B_x = zeros(N_r, N_theta)
    B_z = zeros(N_r, N_theta)

    for i in 1:N_theta
        B_x[:, i] .= B_r[:, i] .* sin(theta[i]) .+ B_theta[:, i] .* cos(theta[i])
        B_z[:, i] .= B_r[:, i] .* cos(theta[i]) .- B_theta[:, i] .* sin(theta[i])
    end

    vp2 = zeros(N_r, N_theta)
    bp2 = zeros(N_r, N_theta)
    alfsurf = zeros(N_r, N_theta)

    for i in 1:N_theta
        vp2[:, i] .= v_x[:, i] .* v_x[:, i] .+ v_z[:, i] .* v_z[:, i]
        bp2[:, i] .= B_x[:, i] .* B_x[:, i] .+ B_z[:, i] .* B_z[:, i]
        alfsurf[:, i] .= 4.0 * π * rho[:, i] .* vp2[:, i] ./ bp2[:, i]
        if any(alfsurf[:, i] .> 1.0) && any(tracer[:, i] .> 0.1)
            alfsurf[:, i] .= 0.0
        end
    end

    return alfsurf
end
alfsurf = zeros(N_files, N_r, N_theta);
for i in 1:N_files
    alfsurf[i, :, :] = alfven_surface(N_r, N_theta, theta, v_r[i], v_theta[i], B_r[i], B_theta[i], rho[i], tracer[i])
end

Here N_r=217 and N_theta=100.
Size of v_r, v_theta, B_r, B_theta, rho, tracer are (1,217,100).

2

Somewhere you’re doing array[i, :, j] and i is a Float64 there, which is not allowed as an index. You can’t use 3.0 for example, only 3.

3 
for i in 1:N_theta

i will range from 1 to 100 so it will be integer.

image
image846×61 3.11 KB

I am getting error in first line of first for loop.

4

Your example is not executable so you cannot expect anyone here to check it in detail for you. The error is clear, so you need to find where you’re picking a floating point number as an index by accident. The i in my example was meant as a placeholder, not referring to your code.

5

likely you are passing in N_theta as a float rather than integer

6

There is only one index that is i and its value lies in range of integer 1 to 100. N_theta is Int64.
N_theta = readdlm(joinpath(directory, "save_grid.out"), skipstart=N_r+10)[1]

7

I just noticed you are passing in

v_r[i], v_theta[i], B_r[i], B_theta[i], rho[i], tracer[i]

note that these getindex calls will be scalar, but I imagined you meant to take a slice? then it should be

v_r[i, : , :], v_theta[i, :, :] ...
1 Like
8

Thank You, Please explain more clearly.

9

most likely the docs can explain more clearly than I can
https://docs.julialang.org/en/v1/manual/arrays/#man-array-indexing

the idea is that if you index into an array with only a single index like A[i], then it will treat A as a flattened object. if you want to index using multiple dimensions that must be explicitly stated like A[x, y, z]

1 Like