Changes

__global__ void Initalize(double* u, double* un, int nx, int nt, double dx)

{

int i = blockIdx.x * blockDim.x + threadIdx.x;

int j = blockIdx.y * blockDim.y + threadIdx.y;

for (int k = 0; k <= nx - 1; k++)

if (k*dx >= 0.5 && k*dx <= 1)

{ u[k * nt] = 2;

__syncthreads();

}

else

{

u[k * nt] = 1;

__syncthreads(); }

}